The mutation is characterized by a high number of CGG-trinucleotide repeats which results in inactivation of the FMR 1-gene through the methylation of the CGG-repeats and upstream CpG-Islands.
Stökkbreytingin lýsir sér í mikilli fjölgun CGG-endurtekninga í geninu og óeðlilegri metýlun CpG-eyja.