ANALYSIS OF UNSTABLE DNA-SEQUENCE IN FRM1 GENE IN POLISH FAMILIES WITH FRAGILE-X SYNDROME

The unstable DNA sequence in the FMR1 gene was analyzed in 85 individu als from Polish families with fragile X syndrome in order to character ize mutations responsible for the disease in Poland. In all affected i ndividuals classified on the basis of clinical features and expression of the fragile site at X(q27.3) a large expansion of the unstable seq uence (full mutation) was detected. About 5% (2 of 43) of individuals with full mutation did not express the fragile site. Among normal alle les, ranging in size from 20 to 41 CGG repeats, allele with 29 repeats was the most frequent (37%). Transmission of premutated and fully mut ated alleles to the offspring was always associated with size increase . No change in repeat number was found when normal alleles were transm itted.