Centromeric alpha-satellite DNA break in reciprocal translocations.

In the process of selecting fluorescence in situ hybridization probes to be used for preimplantation genetic diagnosis in couples with balanced reciprocal translocations, we found 2 individuals with unexpected breaks in the centromeric alpha-satellite DNA. Subsequently, centromere breaks were specifically sought in reciprocal translocations in which 1 or both breakpoints appeared cytogenetically near the centromere. In a total of 11 individuals studied, we found 8 centromere breaks in 6 individuals; in 2 individuals, the alpha-satellite DNA of both chromosomes involved in the translocation split into 2 arrays. These findings suggest that breaks in alpha-satellite DNA are not rare events. Together with those previously reported in the literature, alpha-satellite DNA breaks of at least chromosomes X, 1, 4, 5, 10, 11, 16, 17, 18, and 19 have now been documented. The breaks are familial in 2 of the 6 cases in our study, indicating the derivative chromosomes are both mitotically and meiotically stable. These derivative chromosomes that are either cytogenetically dicentric or molecular cytogenetically dicentric, or have altered amounts of alpha-satellite DNA may prove to be valuable in studying centromere dynamics and biology.