Thursday, January 7, 2010

Cognition and Fragile X syndrome

Fragile X problems persist into adulthood (even though it is considered a pediatric disease). Two separate conditions exist. Patients with the premutation (55-200 repeats of the FMR1 gene) have RNA toxicity but not full blown cognitive abnormalities. RNA toxicity can include primary ovarian insufficiency, fragile X associated tremor ataxia syndrome (FXTAS), fibromyalgia, hypothyroidism, and psychiatric issues such as anxiety and depression. Boys in this range can experience shyness, social anxiety disorders, ADHD and autism spectrum disorders. This is due to excess FMR1 gene.

Patients with the full mutation (greater than 200 repeats) have LACK of FMR1 and Fragile X syndrome (opposite of above in which there is excess RNA present). They present with severe cognitive abnormalities. In boys this manifests as autism, in girls as severe learning disabilities. They also have connective tissue disorders, agression, and psychiatric problems as above. Males with FXS usually have IQ below 70 (severe) but 15 % are "high functioning" with IQ above. High functioning is due to mosaicism within cells or within methylation and the degree of impairment is related to the amount of FMRP present. Among girls, 40 % have a normal IQ, 35 % are borderline, and 25 % have an IQ below 70. The activation percentage (pct of normal X that is active) correlates with disease and that and amount of FMRP available also affects functioning of offspring.

FXS is the most common cause of intellectual impairment and of autism spectrum disease. The full mutation occurs in 1:2500 in population, and the premutation occurs in 1:250 girls and 1:800 boys in the general population. Genetics: FXS patients always have their mother as a carrier. Fathers often pass the premutation on, to their daughters and it does not expand to a full mutation. Mothers with premutation often have expansion to full mutation in their offspring, especially if the number of repeats is greater than 100.

See also posts on FXS and FXTAS on

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