Current concepts in the embryology and genetics of cleft lip … embryo.pdf · Current concepts in...

Clin Plastic Surg 31 (2004) 125–140

Current concepts in the embryology and genetics of

cleft lip and cleft palate

Mary L. Marazita, PhD, FACMGa,b,c,*, Mark P. Mooney, PhDd,e

aCenter for Craniofacial and Dental Genetics, Department of Oral and Maxillofacial Surgery, Division of Oral Biology,

School of Dental Medicine, University of Pittsburgh, Pittsburgh, PA 15219, USAbDepartment of Human Genetics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA

cDepartment of Psychiatry, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USAdDepartments of Oral Medicine & Pathology, and Orthodontics, School of Dental Medicine, University of Pittsburgh,

Pittsburgh, PA 15219, USAeSchool of Arts and Sciences, University of Pittsburgh, Pittsburgh, PA 15219, USA

Clefts of the lip and palate (CL/P) are the most productive counseling. Furthermore, a better under-

common craniofacial birth defects and are among the

most common of all birth defects, with birth preva-

lence ranging from 1 in 500 to 1 in 2000 depending

on the population. Although the severity of orofacial

cleft anomalies varies, multidisciplinary treatment is

often necessary and may include craniofacial surgery;

specialized dental and orthognathic treatment; speech

and hearing intervention; and educational, psychologi-

cal, and social assessment and intervention. The mul-

tidisciplinary nature of cleft care was realized even in

the first recorded surgical repair of a cleft lip (in the

annals of the Chin dynasty in China, about A.D. 390

[1])—detailed postoperative instructions were listed

for optimal results.

Orofacial clefts represent a significant public

health problem due to the significant lifelong mor-

bidity and complex etiology of these disorders. The

extensive psychological, surgical, speech, and dental

involvement emphasize the importance of under-

standing the underlying causes of CL/P to optimize

treatment planning, to predict the long-term course

of any affected individual’s development, to improve

recurrence risk estimation, and to provide pre-re-

0094-1298/04/$ – see front matter D 2004 Elsevier Inc. All right

doi:10.1016/S0094-1298(03)00138-X

* Corresponding author. Suite 500, Cellomics Building,

100 Technology Dr., Pittsburgh, PA 15219.

E-mail address: [email protected]

(M.L. Marazita).

standing of the embryology and genetics of orofacial

clefting is crucial for the development of a biologi-

cally relevant orofacial cleft classification system

[2–4]. The recent identification of specific genes

involved in syndromic and nonsyndromic orofacial

clefting lays the groundwork for cleft classification

based on specific genetic mutations and timing of

craniofacial development rather than on postnatal cra-

niofacial morphology and anatomy [2–5].

This article presents a brief overview of current

concepts in normal and abnormal craniofacial embry-

ology, genetic etiologies of orofacial clefting, and

gene-development interactions that may produce oro-

facial clefts. We encourage the readers to consult more

comprehensive works for additional discussion of

these topics [2–17].

Embryonic development

Early gene expression and signaling molecules in

development

To understand pathologic development, it is fun-

damental to understand and appreciate the complex-

ities of normal development. Genes control early

embryonic development through the production of

transcription factors that can be translated into struc-

tural, regulatory, or enzymatic proteins [10]. These

s reserved.

Table 1

Signaling and growth factors

Factor Abbreviation Derivation Action

Bone morphogenetic proteins BMPs (1–7) Pharyngeal arches;

frontonasal mass

Mesoderm induction; dorso-ventral organizer;

skeletogenesis; neurogenesis

Brain-derived neurotrophic factor BDNF Neural tube Stimulates dorsal root ganglia anlagen

Epidermal growth factor EGF Various organs;

salivary glands

Stimulates proliferation and differentiation of

many cell types

Fibroblastic growth

factors (1–19)

FGFs Various organs and

organizing centers

Neural and mesoderm induction.

Stimulates proliferation of fibroblasts,

endothelium, myoblasts, osteoblasts

Hepatocyte growth factor HGF Pharyngeal arches Cranial motor axon growth; angiogenesis

Homeodomain proteins Hox-a, Hox-b,

PAX

Genome Craniocaudal and dorsoventral patterning

Insulin-like growth

factors 1 and 2

IGF-1

IGF-2

Sympathetic

chain ganglia

Stimulates proliferation of fat and connective

tissues and metabolism

Interleukin-2, Interleukin-3,

Interleukin-4

IL-2, IL-3, IL-4 White blood cells Stimulates proliferation of T-lymphocytes;

hematopoietic growth-factor; B-cell growth factor

Lymphoid enhancer factor 1 Lef1 Neural crest;

mesencephalon

Regulates epithelial–mesenchymal interactions

Nerve growth factor NGF Various organs Promotes axon growth and neuron survival

Platelet-derived growth factor PDGF Platelets Stimulates proliferation of fibroblasts, neurons,

smooth muscle cells, and neuroglia

Sonic hedgehog SHH Various organs Neural plate and craniocaudal

patterning, chondrogenesis

Transcriptional factors TFs Intermediate gene

in mesoderm

induction casade

Stimulates transcription of actin gene

Transforming growth factor-a TGF-a Various organs Promotes differentiation of certain cells

Transforming growth factor-b(Activin A, Activin B)

TGF-b Various organs Mesoderm induction; potentiates or inhibits

responses to other growth factors

Vascular endothelial

growth factor

VEGF Smooth muscle cells Stimulates angiogenesis

Wingless WNT Genome Pattern formation; organizer

From Sperber GH. Craniofacial development. Hamilton, Ontario: B.C. Decker; 2001; with permission.

M.L. Marazita, M.P. Mooney / Clin Plastic Surg 31 (2004) 125–140126

growth factors and morphogens (Table 1) then target

specific embryonic cell populations and their signal

transduction pathways, resulting in the progressive

differentiation, migration, shape changes (morphoge-

netic movements), and programmed cell death (apo-

ptosis) of these cells. These specific activities bring

different groups of embryonic cells into close prox-

imity with each other where inductive biochemical

and biomechanical interactions between these cell

groups may cause certain cell populations to differ-

entiate on their own, even without the continued

presence of the inducing tissue [13]. The molecular

regulation of such interactions and the mechanisms

by which ‘‘pattern’’ development occurs within a

population of cells gives rise to different tissue types

and individual structures, such as bones, muscles,

and teeth.

Although the presence, concentration gradients,

and diffusion patterns of growth factors and signaling

molecules are essential for normal morphogenesis,

intercellular communication and selective permeabil-

ity of cell membranes also act to control and regulate

development. Growth factors stimulate cell prolifer-

ation, differentiation, and permeability through two

general mechanisms. One mechanism involves cer-

tain growth factors (eg, steroids, retinoic acid, and

thyroxin) passing through the plasma cell membrane,

binding with specific receptors, and acting directly on

the genes to alter their function. The second mecha-

nism involves certain other growth factors (eg, fibro-

blast growth factors [FGFs], transforming growth

factor-beta superfamily [TGF-bs], and epidermal

growth factor [EGF]) binding with specific cell sur-

face receptors, activating intracellular signaling path-

Fig. 1. Signaling factors and target genes at different locations and stages of development. (From Johnston MC, Bronsky PT.

Craniofacial embryogenesis: abnormal developmental mechanisms. In: Mooney MP, Siegel MI, editors. Understanding

craniofacial anomalies: the etiopathogenesis of craniosynostosis and facial clefting. New York: John Wiley and Sons; 2002.

p. 61–124; with permission.)

M.L. Marazita, M.P. Mooney / Clin Plastic Surg 31 (2004) 125–140 127

ways (eg, Smad, map-kinase), and eventually causing

gene activation by paracrine activation (Fig. 1). Di-

rect gene activation (the first mechanism) uses ‘‘long

distance’’ endocrine signaling, which is typically more

systemic, potent, of longer duration, and less suscep-

tible to interruption and insult compared with ‘‘short-

distance’’ and localized paracrine signaling. Growth

factors and molecules that function via endocrine

signaling typically are powerful morphogens and

are more potent inducers of craniofacial malforma-

tions [13].

Many signaling molecules (and their receptors)

may be substituted for one another and are present

throughout life. They change their function in the

presence of different concentrations or classes of

growth factors or receptors [10,13]. This redundancy

may account, in part, for the developmental ‘‘plastic-

ity’’ noted during embryogenesis and evolution

[6,7,13]. Gene-controlled, growth factor-induced cell

migrations and cell fusions (fusomorphogenesis) are

essential to organogenesis and normal embryonic

growth [10,18]. Interruptions in these processes typi-

cally produce embryonic death or congenital malfor-

mations [10,13,14].

Germ layer differentiation, neurulation, and midline

malformations

Once the parental sex cells unite and reestablish

the haploid state, the zygote and later the embryo

(1 and 2 weeks postconception) initiate a rapid flurry

of cell growth and differentiation, directed in part by

homeobox genes [10,19]. From this rapidly prolifer-

ating blastocyst develops two distinct germ cell layers

(the embryonic or bilaminar disc stage) by 2 weeks

postconception. During week 3 postconception, the

bilaminar disc is converted into a trilaminar disc

through the process of gastrulation while still under

the direction of homeobox genes [10,19]. It is from

these three primary germ layers (the endoderm, the

mesoderm, and the ectoderm) that the basis of all

subsequent tissue and organ formation arises [9,10].

Hall [6,7,20] suggests that the neural crest cells are a

fourth germ layer in vertebrates.

During week 3 postconception, the neural plate is

derived from the neuroectoderm and extends along

the burgeoning long axis of the disc, forming the

bilateral neural folds and neural tube [10,21]. This is

referred to as the process of neurulation and helps to

M.L. Marazita, M.P. Mooney / Clin P128

determine embryonic polarity (ie, head and tail ends)

[10,21–23]. PAX6, Sonic Hedge-Hog (SHH), and

FGF signaling are involved with neurulation and

with eye formation during this stage (see Table 1

for a summary of genes involved) [10,13,22,23].

The brain and developing placodes are essential for

driving cephalogenesis [5,10,13,24]. Problems in

development during this time may result in midline

neurologic and craniofacial malformations such as

holoprosencephaly (single cavity forebrain), cyclo-

plegias, neural tube defects, and midline orofacial

clefts [5,9,10,13].

Neural crest cell formation, migration, and

differentiation

The ectodermal-derived cells that are found in the

margins of the bilateral neural folds and the transition

zone between the neuroectoderm and epidermis are

referred to as neural crest cells [7,10,13,25–27]. Neu-

ral crest cells migrate as mesenchyme into the devel-

oping embryonic processes of the head and neck

region during neural tube closure (4 weeks postcon-

ception). The pluripotent neural crest stem cells give

rise to a tremendous diversity of cell and tissue types

(eg, neural, pigment, skeletal, connective tissue, car-

diac, dental, and endocrine cells) [6,7,9,10,13,

25–28]. Hall [6,7,20] has suggested that neural crest

cells should be considered a fourth germ layer in

craniate vertebrates because mesoderm and neural

crest cells give rise to a diversity of embryonic meso-

derm. Hall further argues that if mesoderm qualifies

as a secondary germ layer (it is derived secondarily

from ectoderm), then so do neural crest cells.

Neural crest cells migrate in a segmental pattern,

predetermined in part by interactions with hindbrain

neuromeric segments called rhombomeres and par-

axial mesoderm segments called somatomeres (Fig. 2)

[7,10,13]. The neural crest segments migrate into the

developing pharyngeal arches and provide the pre-

cursors of cartilage, bone, muscles, and connective

tissues of the head and neck. The timing and extent of

neural cell migration and differentiation is dependent

on a complex patterning of inductive homeobox gene

(HOX, MSX) signaling between the neural crest and

adjacent neural tube, lateral plate mesoderm, and

epidermis (Fig. 2 and Table 1) [7,10,13,25–27]. De-

ficiencies in neural crest tissue migration or prolif-

eration produce a varied and extensive group of

craniofacial malformations referred to as neurocristo-

pathies, which include von Recklingshausen neuro-

fibromatosis, hemifacial microsomia, orofacial clefts,

and DiGeorge and Treacher Collin syndromes [5,8,

10,13,25,29].

Craniofacial development

The primitive craniofacial complex forms during

week 4 postconception after neural crest tissue migra-

tion, early brain vesicle enlargement, and cranio-

caudal and lateral trunk folding of the trilaminar

disc. Trilaminar disc folding helps incorporate the

endoderm into the body, which in part forms the

mucoepithelial lining of the stomodeum and primitive

oral cavity [9,10,21,30]. A series of inductive events

between the prosencephalon, mesencephalon, and

rhombencephalon and the neural crest tissue that

migrates into the craniofacial complex and pharyngeal

arch apparatus (Fig. 3) helps to form the five facial

prominences (the frontonasal and the bilateral maxil-

lary and mandibular prominences) (Fig. 4) [9,10,

26,31]. It is the differentiation, growth, and eventual

fusion of these prominences that forms the definitive

face. The movement and destination of neural crest

tissues into the facial primordia are controlled in part

by a number of gene families, including (see Table 1)

regulatory homeobox genes (HOXa-1, HOXa-2,

HOXb-1, HOXb-3, and HOXb-4), the SSH gene,

the OTX gene (orthodentical homeobox), the GSC

gene (goosecoid), DLX genes (Drosophila distal-less

homeobox), MSX genes (muscle segment homeo-

box), LHX genes (LIM homeobox), and PRRX genes

(paired-related homeobox) [11,17].

Primary palatogenesis

Normal development. The primary palate is defined

as the portions of the facial primordia that initially

separate the oral and nasal cavities and include the

portions of the medial and lateral nasal processes of

the frontonasal process and the portion of the maxil-

lary processes that contribute to the separation of the

cavities (Fig. 4) [11,13,32]. Normal primary palato-

genesis involves a series of local molecular and

cellular events that are closely timed. Spatial and

biomechanical changes associated with craniofacial

growth must occur in sequence within a critical period

in development (in humans during week 5 to week 7

postconception). The primary palate initially forms

around the developing olfactory placodes with the

rapid proliferation of the lateral epithelium and un-

derlying mesenchyme. These events are controlled in

part by FGFs (FGF8 and FGFR2), bone morphoge-

netic proteins (BMP4 and BMP7), SHH, and retinoic

acid [5,13,32]. Diewert et al [32] have shown that in

human and rodent embryos, as the facial prominences

enlarge around the nasal pits to form the premaxillary

region, growth of supporting brain and craniofacial

components change facial morphology and can affect

the timing, the location, and the extent of contact

lastic Surg 31 (2004) 125–140

Fig. 2. Schematic presentation of the inductive, segmental relationships of different anatomical components in the developing

embryonic head and neck. (A) An overlay of all inductive components showing approximate spacial relationships. (B) Axial and

central nervous system structures. (C) Neural crest cells. (D) Paraxial mesoderm and somatomeres. (E) Arteries and

cardiovascular system. (F) Pharynx and endoderm derived structures. (Modified from Noden DM. Cell movements and control of

patterned tissue assembly during craniofacial development. J Craniof Genet Dev Biol 1991;11:192–213; with permission.) [83]

Fig. 3. The homeotic gene complex of Drosophila (HOM) has been duplicated more or less intact in four different complexes

on different chromosomes of the mouse and human. The same head-to-tail (rostrocaudal) sequence in the chromosomes has been

preserved and corresponds roughly to rostrocaudal gene expression in the neural plate (tube) and neural crest, which is derived

from the neural plate (tube). The newer terminology is used for individual genes, with the older terminology used for mice in

parentheses. Depending on chromosomal positioning, the genes are arranged in paralogous groups 1 through 5 (and beyond) and,

in general, these genes are expressed in a sequential overlapping cascade with one or more active genes being added every two

neuromeres. (Modified from Noden DM. Cell movements and control of patterned tissue assembly during craniofacial de-

velopment. J Craniof Genet Dev Biol 1991;11:192–213; with permission.)

Fig. 4. Stages of facial formation at (A) 4 weeks, (B) 5 weeks, (C) 6 weeks, and (D) 7 weeks. (From Sperber GH. Craniofacial

development. Hamilton, Ontario: B.C. Decker; 2001; with permission.)


between the facial prominences. At the same time, the

forebrain elevates as the cranial base angle decreases,

the medial nasal region narrows, and the maxilla

grows forward to meet the medial and lateral nasal

prominences that relocate with growth of the fore-

brain (see Fig. 4). The upper lip is completed on either

side of the globular prominence (see Fig. 4) by fusing

with the freely projecting medial nasal prominences

of the frontonasal prominence [33]. Such fusion

requires critically timed coordination of growth be-

tween the processes, exact spatial localization, and

apoptosis (or further differentiation) of the epithelium

that forms the transient nasal bridge or fin between

the two processes [32]. The degradation of the un-

derlying nasal fin allows for the uninterrupted move-

ment of mesenchymal cells between the medial and

lateral components of the upper lip by 7 weeks post-

conception (see Fig. 4) [9,10,13,32]. Abnormal de-

velopment of this epithelium may be involved with

clefts of the primary palate.

Additional structures in the primary palate include

the dentition, alveolar and basal bone of the primary

palate, and labial musculature. Typically, four tooth

buds start to develop in the primary palate, anterior to


the incisive fissure, about 4 weeks postconception

[11]. Tooth bud formation is dependent on a large

number of genes (PAX9, MSX1, SHH, DLX, WNT)

and growth factors (nerve growth factor, FGF, and

BMPs), which are expressed in the oral ectoderm and

underlying neural crest tissue [11]. Around 7 weeks

postconception, myogenic mesenchyme, derived from

the sixth somite, migrates into the lip primordia with

accompanying branches of the facial nerve (CNVII)

[9,10,33,34]. Ossification of the primary palate be-

gins around the 8 weeks postconception in the me-

dial nasal prominence and continues laterally to the

maxillary process [11,35].

Orofacial clefting of the primary palate. Many de-

fects in the orofacial tissues that form the primary

palate and surround and support the sensory units are

expressed morphologically as failures of facial promi-

nence merging or fusion resulting in clefts [5,10,11,

13,32]. These defects can be classified as those that

affect the midline (median facial clefts) and those that

occur laterally (lateral facial clefts). Median facial

defects occur early and probably relate closely to the

initial events directing morphogenesis of the anterior

Fig. 5. Defects of orofacial development. (A) Unilateral cleft lip.

cleft lip and nasal defect. (Modified from Sperber GH. Craniofa

with permission.)

midline tissue of the trilaminar disc [5]. Lateral facial

clefts can be conceptualized as defects resulting from

abnormal events usually occurring later in develop-

ment once the facial primordia are in place. It is un-

likely that median and lateral facial cleft defects

are simply the result of single genetic aberrations be-

cause normal craniofacial development results from

many genes inhibiting or enhancing the expression

of others; thus, identifying specific cleft mechanisms

has been difficult.

Additional structures that can be affected by pri-

mary palatal clefting include the dentition, alveolar

and basal bone of the primary palate, and the labial

musculature. Primary palatal clefting occurs most

commonly between the primary and secondary pal-

ates at the incisive fissure that separates the lateral

incisors and canine teeth. Individuals with clefts of

the primary palate may present with dental displace-

ment or dental agenesis from premaxillary hypoplasia

[11]. Labial defects typically involve discontinuity of

the circumoral musculature and reduced lip muscle

volume in cleft embryos and fetuses [33,34]. Re-

cent work from our laboratory [36,37] has detected

subclinical orbicularis oris muscle anomalies visual-

(B) Bilateral cleft lip. (C) Oblique facial cleft. (D) median

cial development. Hamilton, Ontario: B.C. Decker; 2001;


ized using ultrasonography in the ‘‘unaffected’’ rela-

tives of cleft probands. Such morphologies may result

from an initial mesenchymal deficiency during pri-

mary palatogenesis. Embryos and fetuses with clefts

of the primary palate also show delayed ossification

and decreased volume of the premaxilla and anterior

basal bone of the maxilla compared with age-matched

control subjects [35,38]. Such bony morphologies

may result from an initial mesenchymal deficiency

during primary palatogenesis or from later bone re-

sorption due to a lack of functional forces on the pri-

mary palate [39–41].

Secondary palatogenesis

Normal development. The secondary palate is de-

fined as the portions of the facial primordia posterior

to the primary palate and includes the two lateral

palatal processes that project medially from the max-

illary processes. The primordia of the secondary pal-

ate forms the hard (bony) palate, the soft palate (the

velum), the alveolar and basal bone of the maxillae,

and the associated dentition posterior to the incisive

fissure (Fig. 6) [12,13,32].

As with primary palatogenesis, closure and fusion

of the secondary palate requires a complex interaction

of palatal shelf movements, critically timed coordi-

nation of growth between the processes, and apopto-

sis (or further differentiation) of the epithelium along

medial margins of the palatal shelves [2,12,13,32].

During week 8 postconception, the palatal shelves ro-

tate from a vertical position surrounding the tongue

and elevate into horizontal approximation [12,13,32],

with a slight delay in this process noted in female

embryos [42]. Rapid palatal shelf elevation is thought

to result from a number of mechanisms, including de-

Fig. 6. Cleft palate variations. (A) Bifid uvula. (B) Unilateral cleft p

GH. Craniofacial development. Hamilton, Ontario: B.C. Decker; 2

velopmental changes in the connective tissue matrix

and associated glycosaminoglycans of the shelves

leading to hydration, swelling, and rapid elevation; a

change in shelf vascularity leading to increased tissue

fluid pressure and turgor; rapid differential mitotic

growth of the shelf mesenchyme; and movements

of the tongue, facial, and suprahyoid musculature

leading to cranial flexion, swallowing and mandibular

depression, tongue withdrawal from the cleft, and

hence shelf closure [10–13,32]. FGF8 and SHH

expression are found along the medial edge of the

maxillary prominence and presumably are involved in

growth and elevation of the palatal shelves [13]. Once

the palatal shelves are elevated and approximated,

adhesive contact, seam fusion along the medial edges,

and apoptosis of the epithelium are essential for

normal secondary palatogenesis. An increased ex-

pression of the cell adhesion molecule syndecan is

seen during shelf elevation. An increased expression

of TGF-b3 and N-cadherin is also seen along the

medial margins of the palatal shelves, both of which

may cause epithelial apoptosis and differentiation

[12,13,43,46,47].

Before shelf elevation, the tongue-mandibular

complex is small relative to the nasomaxillary com-

plex. The tongue is positioned immediately ventral to

the cranial base, and the head posture is flexed against

the thorax. At the time of palatal shelf elevation, the

tongue and mandible extend beneath the caudal por-

tion of the primary palate, the nasomaxillary complex

lifts up and back relative to the body, and the palatal

shelves elevate above the tongue to occupy the oro-

nasal cavity space. As closure of the secondary palate

progresses, the prominence of mandible increases

and the tongue, attached to the anterior region of

alate and lip. (C) Bilateral cleft palate and lip. (From Sperber

001; with permission.)


Meckel’s cartilage via the genioglossus and genio-

hyoid muscles, also becomes positioned forward in

the oral cavity [32].

Normal fusion of the palatal shelves and primary

palate produces a relatively flat, unarched roof, and

the lines of fusion are seen in the adult skull as the

incisive fissure and midpalatal suture. Ossification of

the palate proceeds from the lateral palatal shelves

and the premaxilla during week 8 postconception.

Myogenic mesenchymal tissue from the first and

fourth pharyngeal arches migrates into the soft palate

and fauces, which accounts for multiple innervation

of the regional musculature—the tensor veli palatini

muscle by the trigeminal nerve (CNV2) and levator

veli palatini and other muscles by the vagus nerve

(CNX) [9–12,30].

Orofacial clefting of the secondary palate. Defects

of the secondary palate are expressed morphologi-

cally as failures of elevation, failures of contact and

adhesion, or failures of fusion resulting in clefts [5,10,

11,13,32]. In humans and in animal models for cleft

palate, wide clefts usually result when shelves remain

in the vertical position, whereas narrow clefts usually

indicate elevated shelves that failed to contact and

fuse or that failed to fuse even if contact was made

[32,44–47]. Major factors shown to limit shelf con-

tact include delayed shelf movement to the horizontal

position, reduction in palatal shelf size, deficient

extracellular matrix accumulation, delayed achieve-

ment of mandibular prominence, head extension (thus

an increase in facial vertical dimension), abnormal

craniofacial morphology, abnormal first arch devel-

opment, increased tongue obstruction of shelf move-

ment secondary to mandibular retrognathia, growth

retardation or chondrodysplasia in Meckel’s cartilage

and increased tongue obstruction to shelf movement

and palatal closure, and amniotic sac rupture leading

to severely constricted fetal head and body posture

[13,32].

Genetic etiologies of orofacial clefting

In this section we summarize the current evidence

regarding genetic etiologies for cleft lip and cleft pal-

ate. Orofacial clefts can occur as part of Mendelian

syndromes, as part of the phenotype resulting from

chromosomal anomalies, or as the result of prenatal

exposure to certain teratogens. Orofacial clefts dem-

onstrate remarkable differences in frequency by gen-

der and laterality. There is an approximate 2:1 ratio

of males to females for CL/P, although slightly

more females than males have CP. Within unilateral

clefts, the ratio of left-sided to right-sided clefts is

also about 2:1. Orofacial cleft birth prevalence shows

a wide range, from about 1/500 births to about

1/2000, depending on population; in general, Asian

and Amerindian populations have the highest fre-

quencies, and African-derived populations have the

lowest frequencies.

Over 300 syndromes exist in which orofacial

clefts are part of the phenotype; about half of these

are due to Mendelian inheritance of alleles at a single

genetic locus. Much progress has been made in recent

years in delineating Mendelian disorders and in gene

discovery of such disorders (refer to the Online

Mendelian Inheritance in Man database available

on the NCBI web site [48] for a catalog of such

disorders). However, only a small portion of indi-

viduals with orofacial clefts has a known etiology

[16,49]. The majority of orofacial clefts are non-

syndromic and are considered complex traits. Given

the public health importance of orofacial clefts [50],

many etiologic studies have been conducted of non-

syndromic orofacial clefts, and many environmental

and genetic factors have been implicated [10,11,13,

32,51,52].

Many genes control early embryonic development

through the production of transcription factors that

can be translated into structural, regulatory, or enzy-

matic proteins [10] (see Table 1); therefore, it is not

surprising that scientists have long felt that orofacial

clefts have a familial basis. The first published de-

scription of a family with several affected members

was in 1757 [53]. Charles Darwin [54] pointed out a

publication of ‘‘the transmission during a century of

hare-lip with a cleft-palate’’ by Sproule [55] describ-

ing the author’s family. Since those early publications,

many statistical analyses of family datasets have been

undertaken to better understand the inheritance pat-

terns of orofacial clefting [56]. The multifactorial

threshold model was proposed to explain many of

the features of nonsyndromic orofacial clefts (such as

the altered gender ratio); however, the predictions of

that specific model could be rejected when tested in

several populations. In the early years of the 20th

century, several seminal works were published regard-

ing the inheritance patterns of orofacial clefts, but

until recently progress has been slow in determining

the exact genes involved. Segregation analyses [56]

and statistical analyses of familial recurrence risk

patterns [57] are consistent with hypotheses of ma-

jor locus involvement or relatively few loci (on the or-

der of 3–14 loci [57]) interacting to cause orofacial

clefts. With statistical evidence that orofacial cleft

family patterns were consistent with genetic inheri-

tance, several groups began linkage and association


studies to identify the genes contributing to the famil-

iality of orofacial clefts.

Etiologic insights from embryology

Most of the environmental and genetic factors im-

plicated in orofacial clefting of the primary palate

[10,11,13,32,51,52] are postulated to produce clefts

by interrupting facial prominence merging or fusion.

A failure of normal disintegration of the nasal fin

or inadequate mesenchymal migration between the

maxillary and medial nasal processes results in bilat-

eral or unilateral clefting of primary palate (ie, lip or

maxillary alveolus) (Fig. 5). Embryonic face shape

[32,58] has also been shown to be related clefts of

the primary palate. Mouse embryos from strains ge-

netically predisposed to primary palatal clefting (the

A/J, A/WySn, and CL/Fr strains) had medial nasal

prominences that were more medially convergent

than normal strain embryos, resulting in decreased

contact with the lateral nasal prominences and a

greater chance of failure of consolidation of tissues.

Embryonic face shape has also been shown to be a

causal factor in genetic predisposition to cleft lip in

mice [59]. Strains susceptible to spontaneous clefts

of the primary palate had a significantly smaller dis-

tance between the nasal pits, different orientation of

medial nasal prominences, a reduction (or absence)

of epithelial activity throughout the developmental

period of primary-palate fusion, and hypoplasia of

the lateral nasal prominences compared with control

strains [13,32]. Embryonic face shape, as a predispo-

sition for primary palatal clefting, may also help ex-

plain the observed ethnic (Asian derived > European

derived > African derived [60]) and gender differ-

ences (males 2:1 over females) in the frequencies of

primary palatal clefting [25,61,62].

There are also clues from our understanding of

embryology with implications for the etiology of the

secondary palate. Hypothesized mechanisms include

abnormal TGF-b isoforms in cleft palate individuals

[63]; unusually wide faces (especially in Asian pop-

ulations), which could move palatal shelves further

apart and prevent adhesion and fusion [64–66] and

which could partly explain the ethnic variability in

palatal clefting (Asian derived > European derived >

African derived) [25,61,62]; tongue-tie (which could

inhibit protrusion of the tongue during shelf eleva-

tion) in a familial form of cleft palate in Iceland [30];

macroglossias in MZ twins discordant for cleft palate

[25]; and a small mandible, as in Pierre Robin se-

quence [13].

When clefts of the primary and secondary palates

are present together (cleft lip plus cleft palate), failure

of secondary palatal closure is thought to occur as a

by-product of the primary palate cleft because of the

resulting alterations in the tongue and palatomaxillary

relationships [67,68].

Chromosomal anomalies

Orofacial clefting is seen as part of the phenotype

in a wide variety of types of chromosomal rearrange-

ments of many chromosomes, including trisomies,

duplications, deletions, micro-deletions, or cryptic

rearrangements [69,70]. Rearrangements that can in-

clude clefts of the primary palate (F the secondary

palate) include deletions of 4p (Wolf-Hirschhorn syn-

drome), 4q or 5p (Cri-du-chat syndrome); duplica-

tions of 3p, 10p, and 11p; and trisomy 13 or 18 (and

trisomy 9 mosaic) [69,70]. Clefts of the secondary

palate alone are seen with deletions of 4q and 7p;

duplications of 3p, 7p, 7q, 8q, 9q, 10p, 11p, 14q, 17q,

19q; and trisomy 9 or 13 [69,70].

The role of micro-deletions and other cryptic

rearrangements in orofacial cleft etiology has recently

been recognized [16]. Such small rearrangements are

notable in cleft etiology because they are often

transmitted within families, unlike the larger rear-

rangements that are more likely to be de novo. Micro-

deletions of 22q11.2 are now known to be the

common etiology for at least three clinically classi-

fied syndromes with clefts of the secondary palate as

a frequent feature (DiGeorge syndrome, velocardio-

facial syndrome, and conotruncal anomaly face syn-

drome; for more details see Gorlin et al [8]).

Single gene etiologies

Almost 300 syndromes have been described in

which a cleft of the lip or palate is a feature [4,8].

About half of those syndromes are due to Mendelian

inheritance of alleles at a single genetic locus, and

great strides have been made in recent years in

mapping genes for such Mendelian disorders. Analo-

gous to the diversity seen in chromosomal abnormal-

ities leading to clefts, every possible Mendelian

pattern is observed in the syndromes that include

orofacial clefts in their phenotypes. About 50% follow

autosomal recessive inheritance, 40% follow autoso-

mal dominant inheritance, and 10% follow X-linked

inheritance (recessive or dominant). Complications

commonly seen in other Mendelian disorders are also

seen in clefting syndromes, such as reduced pene-

trance, variable expressivity, imprinting, allelic het-

erogeneity, and locus heterogeneity. Some patterns of

anomalies can be due to cytogenetic rearrangements

or Mendelian segregation.


Of the 150 Mendelian clefting syndromes, ap-

proximately 30 genes have been cloned [29]. These

genes fall into various classes, including transcription

factors (GLI3, 7p13; PAX3, 2q35—Waardenburg

syndrome; SIX3, 2p21—holoprosencephaly 2; and

SOX9, 17q24.3-q25.1—Camptomelic dysplasia),

extracellular matrix proteins (COL2A1,12q13.1-q

13.2—Stickler syndrome type I; COL11A2, 1p21—

Stickler syndrome type II, and GPC3, Xp22—Simp-

son-Golabi-Behmel syndrome), and cell signaling

molecules (FGFR2, 10q26, Apert-Crouzon syn-

drome; PTCH, 9q22.3—basal cell nevus syndrome;

and SHH, 7q36, holoprosencephaly 3). A full de-

scription of the syndromes that can include an oro-

facial cleft is beyond the scope of this article; please

refer to the online data resources [48] for more

complete details.

One of the major reasons to map and clone genes

for syndromic forms of clefting is to help develop

strategies for delineating the etiology of nonsyndromic

clefting that is by far more common than the syn-

dromic forms. Van der Woude syndrome (VDWS, 1q)

is a clearly Mendelian syndrome that has a phenotype

only slightly more complicated than isolated clefting

(ie, families segregating the VDWS gene exhibit

orofacial clefts [CL/P or CP] paramedian lip pits of

the lower lip, and sometimes hypodontia). VDWS

follows an autosomal dominant inheritance pattern,

with reduced penetrance (individuals carrying the gene

who show no phenotypic features) and variable ex-

pressivity (individuals expressing the phenotype may

have a cleft or lip pits or both, with varying degrees of

severity). Furthermore, VDWS is rare among syn-

dromic forms of clefting in that clefts of the secondary

and primary palates are seen in the same families. The

gene responsible for VDWS (ie, IRF6) has been

recently identified [71] and has shown a strong asso-

ciation with nonsyndromic clefting in a large series of

families from several different populations [72].

Genetic etiologies of nonsyndromic orofacial clefts

Background

Early estimates of the genetic contribution to non-

syndromic orofacial clefts ranged from about 12% to

20%, with the remainder attributed to environmental

factors or gene–environment interactions [73,74]. Es-

timates from more recent studies suggest that about

20% to 50% may be more realistic [49,75–77]. Two

general approaches have been taken to investigate

genetic factors involved in nonsyndromic orofacial

clefting: large scale family studies and linkage/asso-

ciation studies with specific genetic markers.

Statistical segregation analyses of orofacial clefts

investigating primary or secondary cleft palate in

large series of families have consistently resulted in

evidence for genes of major effect [56]. Although one

interpretation of such studies is inheritance at a single

major locus, hypotheses of multiple interacting loci or

genetic heterogeneity cannot be ruled out and were

not explicitly tested in any of the published segrega-

tion analyses to date [56]. Statistical analyses of re-

currence risk patterns [57] have been consistent with

oligenic models with 3 to 14 interacting loci. With

evidence that orofacial cleft family history patterns

are consistent with one or a few loci, there are now

many groups attempting to identify those genes using

the positional cloning approach, beginning with link-

age and association analyses.

Linkage and association studies

The procedures for mapping, cloning, and char-

acterizing genes are now well established, with many

successes for rare Mendelian traits. If nonsyndromic

orofacial clefts can be shown to be linked to or as-

sociated with a marker of known genetic location, it

would be powerful support for a Mendelian genetic

contribution to the etiology. However, only in recent

years have investigators attempted such studies be-

cause nonsyndromic clefting was considered to fol-

low the multifactorial threshold model [78] and thus

would not be amenable to a linkage approach. With

emerging statistical evidence from human family

studies and from knockout mouse experiments in

which one or a few gene(s) can explain clefting etio-

logy, linkage and association studies were launched

in a variety of populations [16,56,57].

Linkage analyses assess the co-segregation of

alleles at a genetic locus of known chromosomal lo-

cation (marker) and a disease locus. Different marker

alleles thus co-segregate with the disease allele in

different families, and the overall frequencies of the

marker alleles calculated from population-based sam-

ples need not vary between affected and control

groups. In this situation, the two loci are said to be

in linkage equilibrium (ie, linked but not associated).

In contrast, if allele frequencies differ significantly

between the affected and control groups, the specific

allele at the marker or candidate locus is said to be

associated with the disease at the population level,

with the most common interpretation of an associa-

tion being linkage disequilibrium. Association meth-

ods are used as an adjunct to linkage approaches for

gene mapping, especially for complex traits [79,80].

Gene mapping studies of orofacial clefts have used

linkage and association methods. Candidate loci or

regions on seven chromosomes (ie, chromosomes 1, 2,

Table 2

Evidence for genes and regions potentially involved in non-

syndromic orofacial clefts

Candidate genesa

Chromosomal

region

Animal

modelsbCandidate

genecGenome

scand

1p36-31 SKI1, LHX8:

K/O, E

MTHFR

(L, A)

L

1q32 IRF6: E IRF6 (A) M

2p13 TGFA: E TGFA (A) L, M

2q35 L, M

3p25 A, M

3q26 TP63: K/O, E L

4p16 MSX1: K/O, E MSX1 (L, A) A

4q31 L

5p15 L, A

6p23 TFAP2A:

K/O, E

F13A1 (L, A) L, M

6q25 L, M

7p13 A, M

7q21 L, A, M

8p21 L, M

8q23 L, M

9q21 L, M

10q25 L

11p12 L, A

12p11 L, A, M

14q12 TGFB3: K/O, E TGFB3 (A) L, M

15q22 L, M

16q L

17p11 L

17q12 KCNJ2: K/O RARA (A) M

18q23

19q13 APOC2/BCL3

(L, A)

L, M

20p12 L, A

Xq21 TBX22: E L

a Candidate genes: genes potentially involved in oro-

facial clefting with evidence from animal models or human

linkage and association studies.b Animal models: genes investigated in animal models

with phenotypes that include clefting. K/O = knockout, E =

expression studies.c Candidate genes/regions: genes and regions with at

least two positive reports of linkage (L) or association (A) in

the literature [16].d Genome scan: regions with positive linkage (L) or

association (A) results with anonymous markers spaced

V10 cM apart throughout the genome (one or more genome

scans [80,81]). M = positive meta-analysis results over all

genome scans.


4, 6, 14, 17, and 19) have positive linkage or asso-

ciation results in CL/P, CP, or both; Table 2 summa-

rizes those candidate genes [16,77]. There are a few

additional loci and chromosomal regions that have

only negative results reported in the literature and are

not presented in detail here. Also, there are many

studies for some loci and few studies for others—this

is not a reflection of the strength of the evidence for

any particular locus; it is merely a reflection of the

interest in particular loci. Table 2 summarizes evidence

from animal models (knock out and expression stud-

ies) for genes on those chromosomes.

Genome-wide scans

In addition to linkage and association studies of

candidate genes for orofacial clefting, genome-wide

scans of large numbers of anonymous markers (ie,

genetic markers of unknown function whose exact

chromosomal location is known) have been con-

ducted [81,82]. Analyses of recurrence risk patterns

[57] suggest that there may be about 3 to 14 genetic

loci involved in nonsyndromic clefts of the primary

palate (F the secondary palate). Given the contradic-

tory results from candidate locus approaches and

given the availability of dense maps of markers,

studies of orofacial clefting are now turning to ge-

nome-wide scans to simultaneously search for multi-

ple regions. Table 2 summarizes those chromosomal

regions with positive results in either or both of

the two published genome scans for nonsyndromic

clefts of the primary palate (F the secondary palate)

[81,82]. Additional genome scans in other popula-

tions and in larger sample sizes are necessary to

confirm these results. Our group has also conducted

a meta-analysis of the published genome scans plus

several other recently completed scans for nonsyn-

dromic clefts of the primary palate (F the secondary

palate) [84]; Table 2 includes a summary of the results

from the meta-analysis (ie, those regions that gave

statistically significant evidence of linkage in the

meta-analysis). There have not been any genome-

wide scans for isolated clefts of the secondary palate.

Summary

Many mechanisms underlying normal and abnor-

mal craniofacial embryogenesis are well understood.

The genetic factors that provoke abnormal develop-

ment and result in orofacial clefts are not clear, but

much progress has occurred in our understanding.

Genes or chromosomal rearrangements on many chro-

mosomes can lead to syndromes that include orofacial

clefts. This diversity in the mechanisms that can lead

to syndromic clefts highlights the fact that the pro-

cesses leading to the development of the oral cavity

and face are complex and sensitive to disturbances at


multiple timepoints or within multiple genetic do-

mains. As for nonsyndromic clefting, large-scale

family studies are consistent with one or a few loci

exerting major effects on phenotypic expression, al-

though no single gene has been identified as a ‘‘nec-

essary’’ locus for development of nonsyndromic

clefts. Rather, the emerging consensus is that the

genetic etiology of nonsyndromic clefting is complex,

with several loci showing significant results in at least

some studies. Some of these loci may be genes for

susceptibility to environmental factors, some may be

modifying loci, and some may be ‘‘necessary’’ loci.

Mutations in genes that are now known to control

early development are logical candidate genes for fu-

ture studies of nonsyndromic orofacial clefting. Con-

tinued genetic analyses and developmental studies are

crucial for eventual understanding of the complex

etiology of these common congenital anomalies.

Acknowledgments

The authors thank Dr. Geoffrey H. Sperber for his

critical reading and constructive comments on the

embryology portion of this manuscript. This work

was supported in part by NIH/NIDCR (DE13078,

MPM; DE09886) (MLM).

References

[1] Khoo B-c. An ancient Chinese text on a cleft lip. Plast

Reconstr Surg 1966;38:89–91.

[2] Shprintzen RJ. Terminology and classification of facial

clefting. In: Mooney MP, Siegel MI, editors. Under-

standing craniofacial anomalies: the etiopathogene-

sis of craniosynostosis and facial clefting. New York:

John Wiley and Sons; 2002. p. 17–28.

[3] Saal HM. Classification and description of nonsyn-

dromic clefts. In: Wyszynski DF, editor. Cleft lip and

palate: from origin to treatment. Oxford: Oxford Uni-

versity Press; 2002. p. 47–52.

[4] Cohen Jr MM. Syndromes with orofacial clefting. In:

Wyszynski DF, editor. Cleft lip and palate: from origin

to treatment. Oxford: Oxford University Press; 2002.

p. 53–65.

[5] Carstens MH. Development of the facial midline. J Cra-

niofac Surg 2002;13:129–87.

[6] Hall BK. Evolutionary developmental biology. Dor-

drecht, the Netherlands: Kluwer Academic; 1998.

[7] Hall BK. The neural crest in development and evolu-

tion. New York: Springer-Verlag; 1999.

[8] Gorlin RJ, Cohen Jr MM, Hennekam RC. Syndromes

of the head and neck. Oxford Monographs on Medi-

cal Genetics no. 42. 4th edition. New York: Oxford

University Press; 2001.

[9] Sperber GH. Craniofacial development. Hamilton,

Ontario: B.C. Decker; 2001.

[10] Sperber GH. Craniofacial embryogenesis: normal de-

velopmental mechanisms. In: Mooney MP, Siegel MI,

editors. Understanding craniofacial anomalies: the etio-

pathogenesis of craniosynostosis and facial clefting.

New York: John Wiley and Sons; 2002. p. 31–60.

[11] Sperber GH. Formation of the primary palate. In: Wys-

zynski DF, editor. Cleft lip and palate: from origin


p. 5–13.

[12] Sperber GH. Palatogenesis: closure of the secondary

palate. In: Wyszynski DF, editor. Cleft lip and palate:

from origin to treatment. Oxford: Oxford University

Press; 2002. p. 14–24.

[13] Johnston MC, Bronsky PT. Craniofacial embryogene-

sis: abnormal developmental mechanisms. In: Mooney

MP, Siegel MI, editors. Understanding craniofacial

anomalies: the etiopathogenesis of craniosynostosis

and facial clefting. New York: John Wiley and Sons;

2002. p. 61–124.

[14] Mooney MP, Siegel MI. Introduction and Overview. In:

Mooney MP, Siegel MI, editors. Understanding cranio-

facial anomalies: The etiopathogenesis of craniosynos-

tosis and facial clefting. New York: John W. Wiley and

Sons; 2002. p. 3–10.

[15] Cohen Jr MM. Syndromes with orofacial clefting. In:

Wyszynski DF, editor. Cleft lip and palate. From origin


p. 53–65.

[16] Marazita ML. Genetic etiologies of facial clefting. In:


facial anomalies: the etiopathogenesis of craniosynos-

tosis and facial clefting. New York: John Wiley and

Sons; 2002. p. 147–62.

[17] Chong SS, Cheah FSH, Jabs EW. Genes implicated in

lip and palate development. In: Wyszynski DF, editor.

Cleft lip and palate: from origin to treatment. Oxford:

Oxford University Press; 2002. p. 25–42.

[18] Shemer G, Podbilewicz B. Fusomorphogenesis: cell

fusion in organ formation. Dev Dyn 2000;218:30–51.

[19] Sharpe PT. Homeobox genes and orofacial develop-

ment. Conn Tiss Res 1995;32:17–25.

[20] Hall BK. The neural crest as a fourth germ layer and

vertebrates as quadroblastic not triloblastic. Evol Dev

2000;2:3–5.

[21] Moore KL, Persaud TVN. The developing human:

clinically oriented anatomy. Philadelphia: W.B. Saun-

ders; 1998.

[22] Streit A, Berliner AJ, Papanayotou C, Sirulnik A, Stern

CD. Initiation of neural induction by FGF signaling

before gastrulation. Nature 2000;406:74–8.

[23] Colas J-F, Schoenwolf GC. Towards a cellular and mo-

lecular understanding of neurulation. Dev Dyn 2001;

221:117–45.

[24] Mooney MP, Siegel MI, Smith TD, Burrows AM. Evo-

lutionary changes in the cranial base and vault: estab-

lishing the primate form. In: Mooney MP, Siegel MI,

editors. Understanding craniofacial anomalies: The


etiopathogenesis of craniosynostosis and facial clefting.

New York: John Wiley and Sons; 2002. p. 275–94.

[25] Johnston MC, Bronsky PT. Prenatal craniofacial devel-

opment: New insights on normal and abnormal mecha-

nisms. Crit Rev Oral Biol Med 1995;6:368–422.

[26] Garcia-Castro M, Bronner-Fraser M. Induction and dif-

ferentiation of the neural crest. Curr Opin Cell Biol

1999;11:695–8.

[27] La Bonne C, Bronner-Fraser M. Molecular mecha-

nisms of neural crest formation. Annu Rev Cell Dev

Biol 1999;15:81–112.

[28] Sarkar S, Petiot A, Copp A. FGF2 promotes skeleto-

genic differentiation of cranial neural crest cells. De-

velop 2001;128:2143–52.

[29] Schutte BC, Murray JC. The many faces and factors of

orofacial clefts. Hum Mol Genet 1999;8:1853–9.

[30] Moore G, Williamson R, Jensson O, Chambers J, Ta-

kakubo F, Newton R. Localization of a mutant gene

for cleft palate and ankyloglossia in an x-linked Ice-

landic family. J Craniofac Genet Dev Biol 1991;11:

372–6.

[31] Coburne MT. Construction for the modern head, cur-

rent concepts in craniofacial development. J Orthod

2000;27:307–14.

[32] Diewert VM, Losanoff S. Animal models of facial

clefting: experimental, congenital, and transgenic. In:


facial anomalies: the etiopathogenesis of craniosynos-

tosis and facial clefting. New York: John Wiley and

Sons; 2002. p. 251–72.

[33] Breitsprecher L, Fanghanel J, Waite P, Steding G,

Gasser R. Gibt es neue Erkenntnisse zur Embryologie

und funktionellen Anatomie der humanen mimischen

Muskulatur und der Oberlippe? Mund Kiefer Gesichst-

Chir 2002;6:102–10.

[34] Mooney MP, Siegel MI, Kimes KR, Todhunter J. De-

velopment of the orbicularis oris muscle in normal and

cleft palate human fetuses using three-dimensional

computer reconstruction. Plast Reconstruc Surg 1988;

81:336–45.

[35] Mooney MP, Siegel MI, Kimes KR, Todhunter JS.

Premaxillary development in normal and cleft palate

human fetuses using three-dimensional computer re-

construction. Cleft Pal-Craniofac J 1991;28:49–53.

[36] Mooney MP, Weinberg SM, Neiswanger K, Faix RS,

Richardson DA, Petiprin SS, et al. Orbicularis oris

muscle morphology in individuals with cleft lip with

or without cleft palate and their relatives. Am J Physiol

Anthropol 2002;34(Suppl):115.

[37] Weinberg SM, Neiswanger K, Mooney MP, Faix RS,

Richardson DA, Petiprin SS, et al. Ultrasound analysis

of orbicularis oris muscle defects in individuals with

cleft lip with or without cleft palate and their relatives.

Am J Hum Genet 2001;69(Suppl):308.

[38] Kjaer I, Keeling JW, Fischer-Hansen B. The prenatal

human cranium: normal and pathologic development.

Copenhagen: Munksgaard; 1999.

[39] Mooney MP, Siegel MI, Kimes KR, Todhunter JS,

Janosky JE. Multivariate analysis of second trimester

midfacial morphology in normal and cleft fetal speci-

mens. Am J Physiol Anthropol 1992;88:203–10.

[40] Siegel MI, Mooney MP, Kimes KR, Gest TR. Traction,

prenatal development and the labioseptopremaxillary

region. Plast Reconstr Surg 1985;76:25–8.

[41] Siegel MI, Mooney MP, Kimes KR, Todhunter JS. De-

velopmental correlates of midfacial components in a

normal and cleft palate fetal sample. Cleft Pal-Cranio-

fac J 1991;28:408–12.

[42] Burdi AR, Faist K. Morphogenesis of the palate in

normal human embryos with special emphasis on the

mechanisms involved. Am J Anat 1967;120:149.

[43] Sun D, Vanderburg CR, Odierna GS, Hay ED.

TGFbeta3 promotes transformation of chicken palate

medial edge epithelium to mesenchyme in vitro. Devel

1998;125:95–105.

[44] Diewert VM. Experimental induction of premature

movement of rat palatal shelves in vivo. J Anat 1979;

129:597–601.

[45] Diewert VM. Correction between alterations in

Meckel’s cartilage and induction of cleft palate with

beta-aminoproprionitrile in the rat. Teratol 1981;25:

43–52.

[46] Kaartainen V, Vonckin JW, Shuler C, Warburton D, Bu

D, Heisterkamp N. Abnormal lung development and

cleft palate in mice lacking TGFbeta3 indicates defects

of epithelial-mesenchymal interaction. Nat Genet 1995;

11:415–21.

[47] Kaartinen V, Cui XM, Heisterkamp N, Groffen J, Shu-

ler CF. Transforming growth factor-beta3 regulates

transdifferentiation of medial edge epithelium during

palatal fusion and associated degradation of the base-

ment membrane. Dev Dyn 1997;209:225–60.

[48] National Center for Biotechnology Information. Avail-

able at: http://www.ncbi.nlm.nih.gov.

[49] Murray JC. Face facts: genes, environment, and clefts.

Am J Med Genet 1995;57:227–32.

[50] Berk NW, Marazita ML. The costs of cleft lip and pal-

ate: personal and societal implications. In: Wysznyski

D, editor. Cleft lip and palate: from origin to treatment.

Oxford: Oxford University Press; 2002. p. 458–67.

[51] Melnick M, Jaskoll T. Molecular studies of facial cleft-

ing: from mouse to man. In: Mooney MP, Siegel

MI, editors. Understanding craniofacial anomalies:

the etiopathogenesis of craniosynostosis and facial

clefting. New York: John Wiley and Sons; 2002.

p. 519–48.

[52] Shashi V, Hart TC. Environmental etiologies of orofa-

cial clefting and craniosynostosis. In: Mooney MP, Sie-

gel MI, editors. Understanding craniofacial anomalies:

the etiopathogenesis of craniosynostosis and facial

clefting. New York: John Wiley and Sons; 2002.

p. 163–206.

[53] Trew CJ. Sistens plura exempla palati deficientis. Nova

Acta Physico-Medica Academiae caesarae Leopol-

dion-Carolinae 1757;1:445–7.

[54] Darwin C. The variation of animals and plants un-

der domestication, vol. 5. New York: Appleton; 1845.

p. 466.

http:\\www.ncbi.nlm.nih.gov


[55] Sproule J. Hereditary nature of hare-lip. BMJ 1863;

1:412.

[56] Marazita ML. Segregation snalysis. In: Wysznyski D,

editor. Cleft lip and palate: from origin to treatment.

Oxford: Oxford University Press; 2002. p. 222–33.

[57] Schliekelman P, Slatkin M. Multiplex relative risk and

estimation of the number of loci underlying an in-

herited disease. Am J Hum Genet 2002;71:1369–85.

[58] Trasler DG. Pathogenesis of cleft lip and its relation to

embryonic face shape in A/J and C57BL mice. Tera-

tology 1968;1:33–50.

[59] Juriloff DM, Trasler DG. Test of the hypothesis that

embryonic face shape is a causal factor in genetic pre-

disposition to cleft lip in mice. Teratology 1976;14:

35–42.

[60] Croen LA, Wasserman CR, Tolarova MM. Racial and

ethnic variations in the prevalence of orofacial clefts in

California, 1983–1992. Am J of Med Genet 1998;79:

42–7.

[61] Oka SW. Dental measurements of orofacial cleft

patients in Mexico: a family study and review of ge-

netics and epidemiology. Pittsburgh: University of

Pittsburgh; 1978.

[62] Ross RB, JohnstonMC. Cleft lip and palate. New York:

Krieger; 1979.

[63] Shiang R, Lidral AC, Ardinger HH, Buetow KH, Ro-

mitti PA, Munger RG. Association of transforming

growth-factor alpha gene polymorphisms with nonsyn-

dromic cleft palate only (CPO). Am J Hum Genet 1993;

53:836–43.

[64] Siegel MI, Mooney MP. Palatal width growth rates as

the genetic determinant of cleft palate. J Craniofac

Genet Devel Biol 1986;2(Suppl):187–91.

[65] Saxen I. Etiological factors in cleft lip and cleft palate.

Duodecim 1976;92:224–6.

[66] Vergato LA, Doerfler RJ, Mooney MP, Siegel MI.

Mouse palatal width growth rates as an ‘‘at risk’’ factor

in the development of cleft palate induced by hypervi-

taminosis A. J Craniofac Genet Dev Biol 1997;17:

204–10.

[67] Diewert VM. A comparative study of craniofacial

growth during secondary palate development in four

strains of mice. J Craniofac Genet Dev Biol 1982;2:

247–63.

[68] Trasler DG, Fraser FC. Role of the tongue in producing

cleft palate in mice with spontaneous cleft lip. Dev

Biol 1963;6:45–60.

[69] Brewer C, Holloway S, Zawalnyski P, Schinzel A,

FitzPatrick D. A chromosomal deletion map of human

malformations. Am J Hum Genet 1998;63:1153–9.

[70] Brewer C, Holloway S, Zawalnyski P, Schinzel A,

FitzPatrick D. A chromosomal duplication map of mal-

formations: regions of suspected haplo- and triplo-

lethality—and tolerance of segmental aneuploidy—in

humans. Am J Hum Genet 1999;64:1702–8.

[71] Kondo S, Schutte BC, Richardson RJ, Bjork BC,

Knight AS, Watanabe Y, et al. Mutations in IRF6 cause

Van der Woude and popliteal pterygium syndromes.

Nat Genet 2002;32:285–9.

[72] Zucchero T, Copper ME, Caprau D, Ribiero L, Suzuki

Y, Yoshiura K, et al. IRF6 is a major modifier for non-

syndromic cleft lip and palate. Am J Hum Genet 2003;

73(suppl):162.

[73] Fogh-Andersen P. Inheritance of harelip and cleft

palate. Copenhagen: Nyt Nordisk Forlag, Arnold

Busck; 1942.

[74] Fogh-Andersen P. Epidemiology and etiology of clefts.

In: Bergsma D, editor. Third conference on the clinical

delineation of birth defects. Baltimore: Williams and

Wilkins; 1971. p. 50–3.

[75] Chung CS, Bixler D, Watanabe T, Koguchi H, Fogh-

Andersen P. Segregation analysis of cleft lip with or

without cleft palate: a comparison of Danish and Japa-

nese data. Am J Hum Genet 1986;39:603–11.

[76] Marazita ML, Spence MA, Melnick M. Genetic analy-

sis of cleft lip with or without cleft palate in Denmark.

Am J Med Genet 1984;19:9–18.

[77] Wyszynski DF, Beaty TH, Maestri NE. Genetics of

nonsyndromic oral clefts revisited. Cleft Palate-Cranio-

facial J 1996;33:406–17.

[78] Carter CO. Genetics of common single malformations.

Br Med Bull 1976;32:21–6.

[79] Ott J. Analysis of human genetic linkage. Baltimore:

Johns Hopkins University Press; 1991.

[80] Marazita ML, Neiswanger K. Association analysis. In:

Wysznyski D, editor. Cleft lip and palate: from origin


p. 240–54.

[81] Prescott NJ, Lees MM, Winter RM, Malcolm S. Identi-

fication of susceptibility loci for nonsyndromic cleft lip

with or without cleft palate in a two stage genome scan

of affected sib-pairs. Hum Genet 2000;106:345–50.

[82] Marazita ML, Field LL, Cooper ME, Tobias R, Maher

BS, Peanchitlertkajorn S, et al. Genome-scan for loci

involved in cleft lip with or without cleft palate in Chi-

nese multiplex families. Am J Hum Genet 2002;71:

349–64.

[83] Noden DM. Cell movements and control of patterned

tissue assembly during craniofacial development.

J Craniof Genet Dev Biol 1991;11:192–213.

[84] Marazita ML, Murray JC, Cooper M, Goldstein T,

Schultz R, Daak-Hirsch S, et al. Meta-analysis of

11 genome scans for cleft lip with or without cleft

palate. Am J Hum Genet 2003;73(suppl):177.

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