Fragile X syndrome

Fragile X Syndrome is the most common inherited cause of mental impairment, and the most common known cause of autism. Fragile X syndrome is a genetic disorder caused by a mutation of the FMR1 gene on the X chromosome, a mutation found in 1 out of every 2000 males and 1 out of every 4000 females. Typically the FMR1 gene contains between 6 and 53 repeats of the CGG codon (trinucleotide repeats). In people with the disorder, the FMR1 allele has over 230 repeats. Expansion to such a degree results in a methylation of that portion of the DNA, effectively silencing the expression of the FMR1 protein. The characteristic constriction of the X chromosome at the chromosomal locus Xq27.3 is caused by this methylation.

Related Topics:
Mental impairment - Autism - Genetic disorder - Mutation - Gene - X chromosome - Male - Female - Codon - Trinucleotide repeats - Allele - Methylation - DNA - Protein - Chromosome

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Because men have only one copy of the X chromosome, males with sufficient trinucleotide expansion are symptomatic, while females have two X chromosomes and thus double the chance of a working allele (unless parents are related). Aside from mental retardation, readily visible characteristics include an elongated face, large or protruding ears, large testicles (macroorchidism), and low muscle tone. Behavioral characteristics may include stereotypic movements (e.g., hand-flapping) and atypical social development, particlularly shyness and limited eye contact. Some individuals with fragile X syndrome also meet diagnostic criteria for autism.

Related Topics:
Female - Allele - Mental retardation - Testicles - Macroorchidism

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While there is no current cure for the syndrome, there is hope that further understanding of the FMR1 gene would allow to counteract the underlying genetic cause. Currently, the syndrome can be treated through behavioral therapy, special education, and when necessary, treatment of physical abnormalities. Persons with Fragile X in their family histories are advised to seek genetic counseling to assess the likelihood of having children who are affected, and how severe any impairments may be in affected descendants.

Related Topics:
Genetic - Behavioral therapy - Special education - Genetic counseling

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