FMR1 gene and fragile X syndrome

Taxonomic features of fragile X syndrome (FXS) associated with the fragile X mutation have evolved over several decades. Males are more severely impac ted cognitively than females, but both show declines in IQ scores as they a ge. Although many males with FXS exhibit autistic-like features, autism doe s not occur more frequently in males with FXS than among males with mental retardation (MR). FXS is caused by inactivation of the FMR1 gene located on Xq27.3. FMRP, the protein produced by FMR1, has been detected in most orga ns and in brain. In cells, it is located primarily in cytoplasm and contain s motifs found in RNA-binding proteins. The FMRP N-terminal contains a func tional nuclear localization signal which permits the protein to shuttle bet ween cytoplasm and nucleus. FMR1 knockout mice show subtle behavioral and v isual-spatial difficulties. Analysis of their brain tissue suggests absence of FMRP impairs synaptic maturation. Individuals with the fragile premutat ion produce FMRP, and the phenotype associated with the premutation has bee n controversial. However, there seems to be a higher incidence of premature ovarian failure in women with the premutation than is found in the general female population. This may be related to unusual increases in mRNA levels in premutation carriers. (C) 2000 Wiley-Liss, Inc.