The FMR1 allele is susceptible to expansion during germline transmission [9]; a full mutation (defined as >200 CGG repeats) of FMR1 leads to an absence or deficiency of the FMR1 protein (FMRP) through epigenetic silencing of the gene, and is the prime cause of fragile X syndrome, while a premutation (55–200 CGG repeats) is characterised by elevated FMR1 transcript expression [10]. The gene discussed is FMR1; the disease is fragile X syndrome.