These findings, with the compelling genetic evidence suggesting the presence in Xq28 of additional genes besides RabGDI1 and FMR2 involved in non-specific X-linked mental retardation (MRX), prompted us to investigate MECP2 in MRX families.
Elucidation of the function of the FMR2 protein as a transcription activator may place FMR2 within the molecular signalling pathways involved in nonspecific X-linked mental retardation (MRX).
Families with mentally retarded males found to be negative for FRAXA and FRAXE mutations are useful in understanding the genetic basis of X-linked mental retardation.
Similar, but a little less known is FRAXE, a fragile site close to that associated with fragile X syndrome, but in this case associated with a mild form of non-specific X-linked mental retardation.
This review summarises the new data on FRAXE associated mental retardation and the FMR2 gene in the light of the recent discoveries of new genes responsible for other forms of non-specific X-linked mental retardation.