Fragile X syndrome (FRAX–A)

Fragile X syndrome is one of a group of disorders caused by
the expansion of a triplet repeat region within a gene. It is
associated with the presence of a fragile site on the X
chromosome (Xq27.3), categorised as FRAX-A. The syndrome
is characterised by mental retardation and accounts for 15–20%
of all X linked mental retardation. Affected males have
moderate to severe mental retardation, whereas affected
females have milder retardation and phenotypic features.