FMR1 CCG-repeat instability by single sperm and lymphocytes of fragile-X premutation males

To determine the meiotic instability of the CGG-triplet repeat in the fragi le-X gene, FMR1, we examined the size of the repeat in single sperm from fo ur premutation males. The males had CGG-repeat sizes of 68, 75, 78, and 100 , as determined in peripheral blood samples. All samples showed a broad ran ge of variations, with expansions more common than contractions. Examinatio n of single lymphocytes indicated that somatic cells were relatively more s table than sperm. Surprisingly, the repeats in sperm from the 75- and 78-re peat males had very different size ranges and distribution patterns despite the similarity of the repeat size and AGG interruption in their somatic ce lls. These results suggest that cis or trans factors may have a role in mal e germline repeat instability.