Fragile+X+Syndrome

Contents:

 * 1) __**What is Fragile X Syndrome?**__
 * 2) Causes of Fragile X Syndrome
 * 3) Effects of Fragile X Syndrome
 * 4) What sould be tested for the Fragil X syndrome? (How do we detect it?)
 * 5) Treatments for Fragile X Syndrome
 * 6) Links

__What is Fragile X Syndrome?__
Several disorders in humans are caused by the inheritance of genes that have undergone insertions of a string of 3 or 4 nucleotides repeated over and over. A locus on the human X chromosome contains such a stretch of nucleotides in which the triplet **CGG** is repeated (CGGCGGCGGCGG, etc.). The number of CGGs may be as few as 5 or as many as 50 without causing a harmful phenotype (these repeated nucleotides are in a noncoding region of the gene). Even 100 repeats usually cause no harm. However, these longer repeats have a tendency to grow longer still from one generation to the next (to as many as 4000 repeats). This causes a constriction in the X chromosome, which makes it quite fragile. It affects 1 in 1200 males of all racial and ethnic groups and those who inherit such a chromosome (only from their mothers, of course) show a number of harmful phenotypic effects including mental retardation. Females who inherit a fragile X (also from their mothers; males with the syndrome seldom become fathers) are only mildly affected. This image shows the pattern of inheritance of the fragile X syndrome in one family. The number of times that the trinucleotide **CGG** is repeated is given under the symbols. The gene is on the X chromosome, so women (circles) have two copies of it; men (squares) have only one. People with a gene containing 80–90 repeats are normal (light red), but this gene is unstable, and the number of repeats can increase into the hundreds in their offspring. Males who inherit such an enlarged gene suffer from the syndrome (solid red squares). (Data from C. T. Caskey, et al.).

__**Symptoms:**__ //Physical:// - Intellectual disability - Elongated face - Large or protuding ears - Flat feet - Large testicles - Low muscle tone //Behavioral:// - Stereotypical movements (eg. hand flapping) - Shyness/limited eye contact - Autism

Causes of Fragile X Syndrome-->