This is one of the causes of leaning disability in children. In fact it is the number 1 inherited cause of mental impairment. About 8% of males with a learning disability have fragile X syndrome. The defect is at the long arm of the X chromosome, near the tip. This site is marked as 27.3, and located here is a gene called gene FMR-1. At this gene location, we see a higher number of CGG repeats. Normal number of repeats is under 54., and a carrier is between 54 and 200. Above 200 we can see clinical picture of the syndrome.
- prominent ears, and having a large head and longish face.
- macro-orchidism, (larger than expected testicles),
- joint problems and speech impairment.
As far as the behaviour is concerned, we can see social avoidance, gaze aversion as well as speech problems. Fragile X syndrome resembles autism. There is a huge range of association between fragile X and autism, between 5 and 46%, is because different studies have used clinical criteria for diagnosing autism.
Autism
This is a developmental learning disorder. Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. The three clinical features are impaired social interactions, impaired communication and restricted repetitive behaviours.
It is a spectrum disorder, therefore each children is different. At one end of the spectrum is the severest form of it called Kanner's Autism and the mild form is called Asperger's Syndrome.
Rett's Syndrom
Phenylketoneuria
This is an autosomal recessive metabolic genetic disorder characterized by an error in the genetic code for the hepatic enzyme phenylalanine hydroxylase, rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine. Build up of phenylalanine causes mental retardation and lack of tyrosine causes fair skin and blue eyes due to failure of melanin production.
Tay-Sachs Disease
This inheritable developmental learning disability is synonymous with the Ashkenazi Jews. The hallmark is hexosaminidase A gene deficiency, and when this hapnes, developmental regression is seen by age of 6 months. Symptoms and signs are motor weakness, loss of vision, fits and infant will die before his or her 3rd birthday. Antenatal diagnosis can be performed by amniocentesis.
Prader Willi Syndrome
There are about 2000 patient with PWS, the hallmark of which are obesity, insatiable hunger and low metabolic rate (thus, high proportion of fat).
Other signs are sleep apnoea, learning disabilities - variable degree : usually mild, outbursts of violent temper and late onset diabetes. A chromosomal disorder caused by lack of paternal 15 q.
Tuberous Sclerosis
