THE FRAGILE-X SYNDROME IN FINLAND - DEMONSTRATION OF A FOUNDER EFFECTBY ANALYSIS OF MICROSATELLITE HAPLOTYPES

Microsatellite markers RS46 (DXS548) and FRAXAC2 flanking the fragile X mutation, an expansion of a (CGG)(n) repeat within the FMR-1 gene, w ere typed in 60 unrelated northern and eastern Finnish fragile X famil ies and in a control population from the same geographical region. A s ignificant difference was found in allelic and haplotypic distribution s between the normal X and fragile X chromosomes. Evidence for a stron g founder effect was detected, with the haplotype 196-153 being presen t on 80% of the fragile X chromosomes, but on only 8% of the normal X chromosomes. In addition to this major haplotype, four minor haplotype s were found on the fragile X chromosomes. These results suggest that the majority of present-day fragile X mutations in Finland may have a common initial ancestor, probably from the 16th century.