Molecular screening of fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic population of Greece and Cyprus: incidence, genetic variation, and stability.

This study presents the first large, population-based molecular investigation of the fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic populations of Greece and Cyprus. The aims of this population screening were to determine the prevalence of FRAXA and FRAXE syndromes among idiopathic mentally retarded (IMR) individuals, to estimate the incidence in the general population, and to investigate the molecular mechanism of instability and expansion of the FMR1-repeat. Ten FRAXA patients were identified to have either the full mutation (eight) or premutation (two) from a Hellenic 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 estimated 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 "gray zone" as well as variation within the 3' end showing polarity of instability. This finding supports the hypothesis that the AGG interspersion and the length of the pure repeat are major factors in determining allele stability. Analysis of FRAXAC1, DXS548, and FRAXAC2 identified particular alleles and haplotypes to have a significant association with either gray zone alleles 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 repeats and, having shared an evolutionary past, would have the tendency to expand.

Cytogenetic and fragile X molecular testing of individuals with mental retardation of unknown etiology.

The aim of this program was to investigate the patients with Mental Retardation Of Unknown Etiology (MROUE), on the island of Cyprus. The MROUE patients were examined cytogenetically for gross chromosomal abnormalities, and by molecular methods for the Fragile X syndrome pathology. Specialized physicians examined all institutionalized or non institutionalized patients throughout Cyprus. Cytogenetic analysis was carried out on 105 individuals, six of which showed various chromosomal aberrations. PCR and Southern blot analysis were carried out on 170 patients referred for exclusion of the Fragile X syndrome. Three patients had positive findings. Although the number of cases elucidated with this general approach was not spectacular, it allowed the resolution of a few clinically equivocal cases, to the satisfaction of the clinicians and, most importantly, the relatives involved. We believe that such screening programs should continue until all cases are thoroughly examined, thus providing definite genetic counseling and psychological support, at least in those cases that are clearly resolved. Equally important is the prospect for prevention through prenatal diagnostic programs, that are already available for such conditions.