FMR1 and fragile X syndrome: In contrast to FXS, reports of AFF2 full expansions are very rare and the dynamics of this repeat is not as clearly characterized as that of FMR1. Indeed, to what extent the alleles with CCG repeats in the range between 36 and 199 may exhibit a pathogenic role remains elusive, in part due to the rarity of the mutation and extended pedigrees[9].