Caused by 55-200 expanded trinucleotide repeats in the FMR1 gene (309550) referred to as a 'premutation' [MISCELLANEOUS] Males are more commonly affected than females [MISCELLANEOUS] Onset in fifties or sixties [MISCELLANEOUS] Caused by trinucleotide repeat expansion (CGG)n in the fragile X messenger ribonucleoprotein gene (FMR1, 309550.0004) [MOLECULAR BASIS] Most patients have a family history of fragile X syndrome [MISCELLANEOUS] Full mutations with expanded trinucleotide repeats greater than 200 result in fragile X mental retardation syndrome (300624) [MISCELLANEOUS]
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