Molecular screening of fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic population of Greece and Cyprus: Incidence, genetic variation, and stability
Pc. Patsalis et al., Molecular screening of fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic population of Greece and Cyprus: Incidence, genetic variation, and stability, AM J MED G, 84(3), 1999, pp. 184-190
This study presents the first large, population-based molecular investigati
on of the fragile X (FRAXA) and FRAXE mental retardation syndromes in the H
ellenic populations of Greece and Cyprus. The aims of this population scree
ning were to determine the prevalence of FRAXA and FRAXE syndromes among id
iopathic mentally retarded (LMR) individuals, to estimate the incidence in
the general population, and to investigate the molecular mechanism of insta
bility and expansion of the FMR1-repeat. Ten FRAXA patients were identified
to have either the full mutation (eight) or premutation (two) from a Helle
nic population of 866 unrelated IMR individuals (611 males and 255 females,
age range 3-25 years), No FRAXE patients were identified among the 611 IMR
males, The incidence of FRAXA in the Hellenic population of Cyprus is esti
mated at 1 in 4,246 males, The repeat sites from the FMR1 and FMR2 alleles
were accurately determined and showed similar distribution and frequencies
with other population studies. The analysis of AGG interspersion within the
FMR1-repeat in normal males revealed long, pure CGG repeats within the "gr
ay zone" as well as variation within the 3' end showing polarity of instabi
lity, This finding supports the hypothesis that the AGG interspersion and t
he length of the pure repeat are major factors in determining allele stabil
ity. Analysis of FRAXAC1, DXS548, and FRAXAC2 identified particular alleles
and haplotypes to have a significant association with either gray zone all
eles or alleles >15 pure CGG repeats. We hypothesize that this subgroup of
alleles and haplotypes are associated with long pure CGGs (>15 CGG) or 35 r
epeats and, having shared an evolutionary past, would have the tendency to
expand. (C) 1999 Wiley-Liss, Inc.