The frequencies of autosomal folate sensitive fragile sites were
compared in populations of mentally retarded fra(X) negative (N = 220)
and normal children (N = 76) in Greece. In addition, the frequency of
autosomal fragile sites was studied in 20 known fra(X) children in order
to test if the fra(X) syndrome is associated with general chromosome
instability.
The frequencies of both common and rare autosomal fragile sites did not
differ significantly between the mentally retarded and the normal
children, although the rate of expression was considerably higher in the
retarded group. Autosomal fragile sites were not increased in the
fra(X) patients. Fra(3)(p14) was by far the most frequent one in all
groups. The frequency of fra(6)(q26) was found to be considerably
higher among the mentally retarded children, this difference being
almost statistically significant. Further cytogenetic studies of normal
and retarded individuals are required in order to elucidate this point
further
