Fragile X syndrome (FXS) is the most common single gene cause of intellectual disability and it is characterized by a CGG expansion of more than 200 repeats in the FMR1 gene, leading to methylation of the promoter and gene silencing. The fragile X premutation, characterized by a 55 to 200 CGG repeat expansion, causes health problems and developmental difficulties in some, but not all, carriers. Fragile X premutation carriers are identified by an expanded
trinucleotide (CGG) expansion in the 5â untranslated region of the FMR1 gene. In the past, research mainly focused on the individuals with the full mutation with fragile X syndrome (FXS) and carriers were thought to be unaffected. FMRP, the protein produced by the FMR1 gene, is important in embryonic development, including the differentiation and migration
of neurons and glia cells, for regulation of synaptic plasticity throughout life and for adult neurogenesis. The diagnostic criteria for FXTAS were described after the original patients were reported .The original diagnostic guidelines for FXTAS based on clinical reports were later expanded to include characteristic FXTAS eosinophilic intranuclear inclusions that are seen in neurons and astrocytes throughout the brain of individuals with FXTAS. FXTAS is characterized by intention tremor, ataxia leading to frequent falling, peripheral neuropathy, autonomic dysfunctionincluding hypertension, orthostatic hypotension, and cognitive decline.
Randi Hagerman, Molecular Advances Leading to Treatment Implications for Fragile X
Last date updated on June, 2014