Molecular Cytogenetic Characterization of Rare but Repeatedly Observed Translocations

Balanced chromosomal rearrangements, including translocations, contribute to infertility, repeated abortions, and/or genetically imbalanced offspring in corresponding carriers. A translocation is usually considered a unique, <em>de novo,</em> or familial event. Besides, some translocations have also been shown to develop multiple times with slightly different or even identical breakpoints; for others, founder effects have been suggested. Here, two known recurrent translocations [t(11;22)(q23.3;q11.21) and der(X)t(X; Y)(p22.32;p11.31)] and two possibly at low frequencies repeatedly observable translocation events [t(5;16)(q13.3~14.1;p13.3) and t(Y;12)(q11.23;q12)] were studied. In the here applied molecular cytogenetic setting, it could be confirmed that the translocation t(11;22)(q23.3;q11.21) has its breakpoints in chromosome 11 between 116.585061 and 116.774263 Mb (GRCh37/hg19) and in chromosome 22 between 21.502000 and 21.616240 Mb (GRCh37/hg19). Corresponding suited bacterial artificial chromosome probes are suggested for their unequivocal characterization. For der(X)t(X;Y)(p22.32;p11.31) seen in 46, XX males, it could be confirmed that there is a significant variance in the derivative X-chromosome’ breakpoints and two new breakpoints are reported for one case. Breakpoints could also be narrowed down for two cases, each of a balanced translocation t(5;16)(q13.3~14.1;p13.3) and t(Y;12)(q11.23;q12). For the latter two cases, further studies need to show if these are more often observable rearrangements in infertile. Overall, it seems worthwhile considering translocations as inversions, as possibly regularly observable recurrent chromosomal rearrangements in human (infertile) populations, in which the formation mechanisms are still far from being understood. The contribution of such rearrangements to the genetic variety of the human population has not fully assessed yet.