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Transcript of Genetic Syndromes Chromosomes Sex Linked Syndromes Gene Defects Development of Young Children with...
Genetic Syndromes
Chromosomes
Sex Linked SyndromesSex Linked Syndromes
Gene DefectsGene Defects
Development of Young Children with Disabilities#872.514 (61)
Carol Ann Heath
What is a Trisomy?
A chromosomal anomaly characterized by the presence of an extra chromosome in the cells
A trisomy occurs when there are 47 chromosomes instead of 46
A partial trisomy occurs when just part of an extra chromosome attaches to another
Trisomy continued
Mosaic trisomy occurs when the extra chromosome material is not present in every cell
The most common known trisomies are:
Trisomy 21 (Down syndrome)Trisomy 18 (Edward’s syndrome)Trisomy 13 (Patau’s syndrome)
Trisomy 21: Down syndrome
Extra 21st chromosome; 47 chromosomes in each cell
1/800 birthsApproximately 5,000 children with Downsyndrome born each year in U.S.1% chance of reoccurrenceLife expectancy: approximately 55
years
Down syndrome
96% of children with Down syndrome have the extra chromosome 21
4% have either a translocation (attached to or incorporated into another chromosome in the egg or sperm) or a form called “Mosaic” in which not all cells affected.
Mosaic children may be less delayed
Prevalence
Prevalence increases with maternal age:
29 years and younger 1/150030-34 years 1/80035-39 years 1/27040-44 years 1/100over 45 years 1/50
Physical Characteristics
Hypotonia short neckoval-shaped eyes (excess skin)epicanthal foldssingle palmar creasessmall noseflattened nasal bridgesmall oral cavitysmall ears that may fold slightly at top
Health problems associated with Down syndrome
40-50% have congenital heart defectsRespiratory problems, especially upper
respiratory infectionsEye and ear problems including hearing
lossThyroid problemsCervical spine abnormalitiesGastrointestinal problems
Down syndrome continued
Most have some degree of mental retardation ranging from mild to severe.
Average person functions in mild to moderate range.
Education in public schoolsPerform daily living skills independentlyCan marry and have children (rare for
men)Women have 50% their child will have DS
Development
Better prognosis due to:better health careearly interventionmore normal family and social
experiencesbetter educational opportunitiesmore positive social attitudes
Development continued
Social and emotional development in infancy delayed, they progress in the first year is essentially normal.
Hypotonia delays motor skills which restricts their early experiences.
Visual exploration and eye-contact delayed in first year.
Development continued
Expressive language skills delayedMay be able to sign words before
verbalizing them3/4 children have speech production
problems4/5 may experience some degree of
hearing loss (fluctuating caused by o.m.)
Development continued
Many children have auditory-perceptual impairment (tree/cheese)
At risk for dyspraxia-inability to perform coordinated movements
Benefits of sign language
A way of teaching speech and language
Method of communicating and expression
Develop comprehension of speech
Reading
Most early reading books contain too little text and text that is too complex
Reading single words first:matchingselectingnaming
Trisomy 13
Sometimes referred to as Patau SyndromeDescribed in 1657, etiology not
discovered until 1960 by Dr. Klaus PatauExtra 13th chromosome which results in
significant multiple defects in major organ systems
Brain most severely affectedMany born blind, deaf, no sense of smell
Trisomy 13
1/8000 birthsMedian survival is 2.5 days82% die within the first month5% survive first 6 monthsThose surviving longer have severe
mental defects, seizures, and failure to thrive
Only 1 adult known to survive to age 33
Abnormalities
80% heart defect60-80% cleft lip, cleft palate or bothFound in 50% or more patients:central nervous system hearingcranium eyesskin hands and feetskeletal genitalia
Etiology
Maternal age has been a factor with occurrence
Chance of recurrence is thought to be low
Trisomy 13 mosaicism usually show a less severe clinical phenotype, survival may be longer, and mental deficiency variable
Trisomy 18
Also known as Edward’s syndromeDiscovered in 1960 by Dr. John
EdwardsCaused by an extra 18th chromosomeIt is the second most common multiple
malformation syndrome1/6,600 birthsAffects females 3:1
Trisomy 18
50% die within first weekOnly 5-10% survive the first year as
“severely mentally defective individuals”10 children over the age of 10 reportedMost unable to walk and language limited,
but some older children who survive may interact and relate to family members.
Abnormalities
Growth deficiency congenital anomalies of the heart,
lung, kidneys, and diaphragmincreased muscle tonesmall mouth and jawmental deficiencymicrocephaly
Abnormalities continued
Low set malformed earssmall pelvis, limited hip abductionunderdeveloped nailsunderdeveloped or absent thumbsabnormal genitaliaepiscanthal folds
Etiology
Maternal age contributing factor to occurrence
1% chance of recurrenceMoscaicism leads to partial clinical
expression, longer survival and various degrees of variations
Sex Linked
Abnormality in the overall number of chromosomes for X and Y
Male has one X and One YFemale has two X
Disorders
Turner syndrome: female abnormalityFemale has only one X, total of 45,
not 46 chromosomes, resulting in XO pattern
Only case in which too few chromosomes can develop into an embryo and survive
1/5000 female births
Turners
Very short <5 ftLowered hairline, broad chest and
short neckOvaries do not function normallyIQ in typical range with learning
disabilities, particularly visual-perceptual and mathematics
Klinefelter syndrome
Males has extra X chromosome, resulting in 47
Pattern of XXY1/500 malesTaller and thinner; underdeveloped
secondary sex traits; decreased hormone level
Language delays; normal adulthood
Chromosome deletions
Sometimes genetic material is missing from a chromosome. These chromosomes are said to have “deletions”.
Interstitial deletions occur when a chromosome has broken, genetic material has been lost, and the chromosome arms rejoin
Larger deletions lead to death
Cri du chat syndrome
First described in 1963 by LejeuneSyndrome associated with deletion of
the short arm of chromosome5Deletion can vary in size from
extremely small (involving only one band) to the entire short arm
Majority of children die in early childhood, some survive into adulthood with low IQ
Abnormalities
Low birth weight 72%Slow growth 100%cat-like cry 100%hypotonia 78%mental deficiency 100%microcephaly 100%strabismus 61%
Abnormalities continued
Round face 68%epicanthal folds 85%Low set and/or poorly
formed ears 57%congenital heart disease 30%
Development
As babies, unusually squirmyCat-like cry that becomes less prominent
with ageWith special schooling and supportive
home environment, some children have attained social and psychomotor skills of a 5 to 6 year old
50% had vocabulary adequate for communication
William syndrome
Described in 1961 by Williamsdeletion of one allele located within
chromosome subunit 7q11.231/20,000 births
Abnormalities
Mild growth deficiencymild microcephalysmall upturned noselong philtrumepicanthal foldscardiac anomaliesjoint limitations
Performance
Average IQ is 56 (range 40-80)Hoarse voiceHypersensitive to soundMild neurologic dysfunctionPoor coordinationDecreased perceptual and motor functionLanguage ability much greater than
cognitive ability
Development
Infancy: feeding problems, colicky, fretful
Childhood: outgoing, no fear of strangers, strong interest in others
2/3 of children: difficult temperament, more negative moods, increased activity, distractible, less persistence, and low threshold arousal
Development continued
As adults: progressive medical problems
Most live with parents or in group home
Sudden death reported in a number of children
Deletion #22q11.2 syndrome
Previously known as DiGeorge syndrome1 out 5000 birthsCommon cause of genetic heart
malformationFacial anomalities: small mouth, narrow
eyes, bulbous nose, palate Immune deficiencyTypical cognitive ranges with learning
disabilities, particularly in math
Mental Impairment
Females: learning disabled in math exceptional with reading and spelling 1/3 have mental disabilities similar to those
associated with schizophreniaMales:
process information in simultaneous fashion Sees whole in order to understand the parts
Speech and Language
Rapid burstsEcholalicPerseveration most difficulty for malesTalking inappropriatelyOne topicSpeech problems made worse if
anxious
Behavioral Problems
ADHDTemper tantrumsMood swingsAggressionStrong reaction to change in
environmentSensory integrationAutistic like behaviors
Medical Problems
At greater risk for otitis mediaMyopia“Lazy eye”Orthopedic difficulties related to flat
feet and joint laxity20% of males prone to seizuresDigestive disorders
Education
Early InterventionMainstreamingOccupational therapySpeech therapyPhysical therapyVisual devices
Fragile XFragile X
Identified by a break or weakness on the long arm of the X chromosome
FMR-1X linked“Genetic anticipation”Testing for Fragile X
Fragile X syndromeFragile X syndrome
Most Common Genetically inherited form of mental retardation
1991 clinical method of diagnosing
Occurs in 1/1000 male birthsOccurs in 1/2500 female birthsLife span is normal
Physical Characteristics
Long narrow faceLarge or prominent earsMacroorchidismAbnormalities of connective tissue:
double jointed fingersFlat feetHeart Murmur
Mental Impairment
80% of males have mental impairment ranging from severe retardation to low-normal intelligence
Majority: mildly to moderately retarded30% of females have some degree of
mental retardationIQ appears to decline with age