"The underlying genetic abnormality is an expansion of a trinucleotide repeat (CGG) in the 5` untranslated region fragile X messenger ribonucleoprotein 1 (FMR1) gene that encodes for the fragile X messenger ribonucleoprotein (FMRP) 1-3. This repeat is inherently unstable and can result in an expansion of the repeat during maternal transmission 3."
"When 55-200 repeats are present there are excessive levels of FMR1 mRNA transcription but despite this, the actual levels of FMRP are reduced 3. Generally, most premutation carriers are phenotypically normal, however, approximately 25% demonstrate some subtle physical changes 2. Emotional difficulties are also reported 2. Specific sex-dependent phenotypic manifestations are also encountered:"
"Once more than 200 repeats are present a cascade of events takes place resulting in the eventual methylation of the promoter region of the FMR1 gene which in turn silences the gene resulting in a lack of FMRP and resultant fragile X syndrome 2,3."
"At this time there are no accepted gene therapies or FMRP replacement therapies available, although both approaches are being researched."
"Fragile X syndrome"
Expected headings
"Premutation"
"Fragile X syndrome"