Shaina Mavreen D. Villaroza

IV-Electron

BIOLOGY 3

1. Wolf-Hirschhorn Syndrome: Wolf–Hirschhorn syndrome (WHS), also known

as chromosome deletion Dillan 4p syndrome, Pitt-Rogers-Danks syndrome (PRDS) or Pitt syndrome, was first described in 1961 by Americans Herbert L. Cooper and Kurt Hirschhorn and, thereafter, gained worldwide attention by publications by the German Ulrich Wolf, and Hirschhorn and their co-workers, specifically their articles in the German scientific magazine Humangenetik. It is a characteristic phenotype resulting from a partial deletion of chromosomal material of the short arm of chromosome 4.

The signs and symptoms of Wolf-Hirschhorn are related to the loss of multiple genes on the short arm of chromosome 4. WHSC1, LETM1, and MSX1 are the genes that are deleted in people with the typical signs and symptoms of this disorder. These genes play significant roles in early development, although many of their specific functions are unknown. Researchers believe that loss of the WHSC1 gene is associated with many of the characteristic features of Wolf-Hirschhorn syndrome, including the distinctive facial appearance and developmental delay. Deletion of the LETM1 gene appears to be associated with seizures or other abnormal electrical activity in the brain. A loss of the MSX1 gene may be responsible for the dental abnormalities and cleft lip and/or palate that are often seen with this condition.

2. Jacobsen Syndrome Jacobsen Syndrome, also known as 11q

deletion disorder, is a rare congenital disorder resulting from deletion of a terminal region of chromosome 11 that includes band 11q24.1. It can cause intellectual disabilities, a distinctive facial appearance, and a variety of physical problems including heart defects and a bleeding disorder. The syndrome was first identified by Danish physician Petra Jacobsen, and is believed to occur in approximately 1 out of every 100,000 births.

Other features of Jacobsen syndrome can include heart defects, feeding difficulties in infancy, short stature, frequent ear and sinus infections, and skeletal abnormalities. The disorder can also affect the digestive system, kidneys, and genitalia. The life expectancy of people with Jacobsen syndrome is unknown, although affected individuals have lived into adulthood.

3. Cri-du-chat Syndrome Cri du chat syndrome, also known as

chromosome 5p deletion syndrome, 5p minus syndrome or Lejeune’s syndrome is a rare genetic disorder due to a missing part of chromosome 5. Its name is a French term (cat-cry or call of the cat) referring to the characteristic cat-like cry of affected children. It was first described by Jérôme Lejeune in 1963. The condition affects an estimated 1 in 50,000 live births, strikes all ethnicities, and is more common in females by a 4:3 ratio.

The syndrome gets its name from the characteristic cry of affected infants, which is similar to that of a meowing kitten, due to problems with the larynx and nervous system. About 1/3 of children lose the cry by age 2. Other symptoms of cri du chat syndrome may include:

feeding problems because of difficulty swallowing and sucking.

low birth weight and poor growth. severe cognitive, speech, and motor delays. behavioral problems such as hyperactivity, aggression, tantrums, and

repetitive movements. unusual facial features which may change over time. excessive drooling. constipation.

4. Rett SyndromeRett syndrome is a neurological and developmental disorder that mostly

occurs in females.  Infants with Rett syndrome seem to grow and develop normally at first, but then stop developing and even lose skills and abilities.

For instance, they stop talking even though they used to say certain words.  They lose their ability to walk properly.  They stop using their hands to do things and often develop stereotyped hand movements, such as wringing, clapping, or patting their hands. 

Rett syndrome is considered one of the autism spectrum disorders. Most cases of Rett syndrome are caused by a mutation on the MECP2 gene, which is found on the X chromosome.

Some argue that it is misclassified as an autism spectrum disorder, just as it would be to include such disorders as fragile X syndrome, tuberous sclerosis, or Down syndrome where one can see autistic features. However, it has been suggested that it be removed from the DSM-5, because it has a specific etiology.

It has also been argued that Rett Syndrome is in fact a neurodegenerative condition as opposed to a neurodevelopmental condition. This was shown by the fact that mice with induced Rett Syndrome can have their neurons completely restored

and a normal phenotype by adding the MECP2 gene back to their genome. This information has also helped lead to further studies in curing or treating the disorder.

It was first described by Austrian pediatrician Andreas Rett in 1966.

5. Duchene Muscular Dystrophy Duchenne muscular dystrophy (DMD) is a

recessive X-linked form of muscular dystrophy, affecting around 1 in 3,600 boys, which results in muscle degeneration and eventual death. The disorder is caused by a mutation in the dystrophin gene, located on the human X chromosome, which codes for the protein dystrophin, an important structural component within muscle tissue that provides structural stability to the dystroglycan complex (DGC) of the cell membrane. While both sexes can carry the mutation, females rarely exhibit signs of the disease.

Symptoms usually appear in male children before age 5 and may be visible in early infancy. Even though symptoms do not appear until early infancy, there is laboratory evidence, which can distinguish a child with the disease at birth. Progressive proximal muscle weakness of the legs and pelvis associated with a loss of muscle mass is observed first. Eventually this weakness spreads to the arms, neck, and other areas. Early signs may include pseudohypertrophy (enlargement of calf and deltoid muscles), low endurance, and difficulties in standing unaided or inability to ascend staircases. As the condition progresses, muscle tissue experiences wasting and is eventually replaced by fat and fibrotic tissue (fibrosis). By age 10, braces may be required to aid in walking but most patients are wheelchair dependent by age 12. Later symptoms may include abnormal bone development that lead to skeletal deformities, including curvature of the spine. Due to progressive deterioration of muscle, loss of movement occurs, eventually leading to paralysis. Intellectual impairment may or may not be present but if present, does not progressively worsen as the child ages. The average life expectancy for patients afflicted with DMD is around 25.

6. Charcot-Marie-Tooth Disease Type IA The most common cause of CMT (70-80% of

the cases) is the duplication of a large region in chromosome 17p12 that includes the gene PMP22. Some mutations affect the gene MFN2, which codes for a mitochondrial protein. Cells contain separate sets of genes in their nucleus and in their mitochondria. In nerve cells, the mitochondria travel down the long axons. In some forms of CMT, mutated MFN2 causes the mitochondria to form large clusters, or clots, which are unable to travel down the axon towards the synapses. This prevents the synapses from functioning.

Type 1 Charcot-Marie-Tooth disease is characterized by abnormalities in myelin, the protective substance that covers nerve cells. Type 2 Charcot-Marie-Tooth disease is characterized by abnormalities in the fiber, or axon, that extends from a nerve cell and transmits nerve impulses. Type 4 Charcot-Marie-Tooth disease affects either the axon or myelin and is distinguished by its pattern of inheritance. In intermediate forms of Charcot-Marie-Tooth disease, abnormalities occur in both axons and myelin. Type X Charcot-Marie-Tooth disease is caused by mutations in a gene on the X chromosome, one of the two sex chromosomes. Within the various types of Charcot-Marie-Tooth disease, subtypes (such as 1A, 2A, 4A, and X1) are distinguished by the specific gene that is altered.

Charcot-Marie-Tooth disease is a group of progressive disorders that affect the peripheral nerves and result in problems with movement and sensation. Peripheral nerves connect the brain and spinal cord to muscles and to sensory cells that detect sensations such as touch, pain, heat, and sound.

7. Edwards Syndrome Edwards syndrome (also known as Trisomy 18 (T18)

or Trisomy E) is a genetic disorder caused by the presence of all or part of an extra 18th chromosome. This genetic condition almost always results from nondisjunction during meiosis. It is named after John H. Edwards, who first described the syndrome in 1960. It is the second most common autosomal trisomy after Down syndrome that carries to term.

Affected individuals may have heart defects and abnormalities of other organs that develop before birth. Other features of trisomy 18 include a small, abnormally shaped head; a small jaw and mouth; and clenched fists with overlapping fingers.

Edwards syndrome occurs in around one in 6,000 live births and around 80 percent of those affected are female. The majority of fetuses with the syndrome die before birth. The incidence increases as the mother's age increases. The syndrome has a very low rate of survival, resulting from heart abnormalities, kidney malformations, and other internal organ disorders.

8. Patau SyndromePatau syndrome is a syndrome caused by a chromosomal abnormality, in

which some or all of the cells of the body contain extra genetic material from chromosome 13. This can occur either because each cell contains a full extra copy of chromosome 13 (a disorder known as trisomy 13 or trisomy D), or because each cell contains an extra partial copy of the chromosome (i.e., Robertsonian translocation) or

because of mosaic Patau syndrome. Full trisomy 13 is caused by nondisjunction of chromosomes during meiosis (the mosaic form is caused by nondisjunction during mitosis). In Patau syndrome, the extra genetic material from chromosome 13 disrupts the normal course of development, causing severe heart and kidney defects, amongst other features characteristic of Patau syndrome. Like all nondisjunction conditions (such as Down syndrome and Edwards syndrome), the risk of this syndrome in the offspring increases with maternal age at pregnancy, with about 31 years being the average. Patau syndrome affects somewhere between 1 in 10,000 and 1 in 21,700 live births.

Newborns with Patau syndrome share common physical characteristics: Extra fingers or toes (polydactyly) Deformed feet, known as rocker-bottom feet Neurological problems such as small head (microcephaly), failure of

the brain to divide into halves during gestation (holoprosencephaly), severe mental deficiency

Facial defects such as small eyes (microphthalmia), absent or malformed nose, cleft lip and/or cleft palate

Heart defects (80% of individuals) Kidney defects

9. Down Syndrome Down syndrome (DS) or Down's syndrome,

also known as trisomy 21, is a chromosomal condition caused by the presence of all or part of a third copy of chromosome 21. Down syndrome is the most common chromosome abnormality in humans. It is typically associated with a delay in cognitive ability (mental retardation, or MR) and physical growth, and a particular set of facial characteristics. The average IQ of young adults with Down syndrome is around 50, compared to children without the condition with an IQ of 100. A large proportion of individuals with Down syndrome have a severe degree of intellectual disability.

The physical features and medical problems associated with Down syndrome can vary widely from child to child. While some kids with DS need a lot of medical attention, others lead healthy lives.

Down syndrome is named after John Langdon Down, the British physician who described the syndrome in 1866.

10. Philadelphia Syndrome Philadelphia chromosome or Philadelphia

translocation is a specific chromosomal abnormality that is associated with chronic myelogenous leukemia (CML). It is the result of a reciprocal translocation between chromosome 9 and 22, and is specifically designated t(9;22)(q34;q11). The presence of this translocation is a highly sensitive test for CML, since 95% of people with CML have this abnormality (the remainder has either a cryptic translocation that is invisible on G-banded chromosome preparations, or a variant translocation involving another chromosome or chromosomes as well as the long arm of chromosomes 9 and 22). However, the presence of the Philadelphia (Ph) chromosome is not sufficiently specific to diagnose CML, since it is also found in acute lymphoblastic leukemia (ALL, 25–30% in adult and 2–10% in pediatric cases) and occasionally in acute myelogenous leukemia (AML).

Sources: About.com

GeneticsHomeReferrence.com KidsHealth.org National Institutes of Health, Eunice Kennedy Shriver,

National Institute of Child Health & Human Development Wikipedia.org