[Inter-generational transmission of mutations responsible for fragile X syndrome]

Inter-generational transmission of normal and mutated (CGG)n sequences in the FMR1 gene was studied in 17 Polish fragile X families. All normal alleles were stable when transmitted to the progeny. Twenty-five of the 26 transmitted maternal premutations expanded to full mutation level. No correlation between the number of CGG repeats in the maternal premutation and the size of the mutation in the offspring was found. Analysis of the mutation size in siblings revealed that the length of full mutations is sex-dependent. The average length of the (CGG)n sequence in sons of fragile X female carriers was larger than in daughters.