Fragile X syndrome, the most common cause of inherited mental retardation, is caused by expansion of an unstable CGG repeat (? 200 CGG repeats) in the promoter region of the FMRI gene on the X chromosome. Expansions lead to methylation and silencing of the gene. Fragile X-associated tremor ataxia syndrome (FXTAS) is the phenotype seen in carriers of FMR1 premutation (CGG repeats 55-200). It is characterized by action tremor, ataxia, cognitive impairment (memory and executive dysfunction), parkinsonism, psychiatric disorders, peripheral neuropathy, and autonomic failure. Brain MRI characteristically demonstrates increased T2 signal intensity in the middle cerebellar peduncles.
Haitham M Hussein MD, Departments of Neurology, University of Minnesota, Minneapolis, MN
Disclosure: Dr. Hussein has nothing to disclose.
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