FMR1 gene encodes for the Fragile X Mental Retardation Protein, a member of the RNA-binding proteins family, which plays a role in intracellular RNA transport and in the regulation of translation of target mRNAs. The gene normally has 6-53 copies of the 5' UTR trinucleotide repeat (CGG). Expansion of these repeats or abnormal DNA methylation is the main cause of fragile X syndrome; it may also cause one form of premature ovarian failure (POF1). There are two types of mutations in the FMR1 gene: the premutations characterized by moderate expansions of the repeat and not causing mental retardation, while the full mutation types involve larger expansions of the repeat with abnormal methylation of the neighboring CpG island.