Translocations involving chromosome 12. I. A report of a 12,21 translocation in a woman with recurrent abortions, and a study of the breakpoints and modes of ascertainment of translocations involving chromosome 12.

A translocation t(12;21)(q24.1;q21.5) is described in a woman with a history of recurrent spontaneous abortions. The break points of this translocation are compared with those of 30 other translocations described in the literature, and the following conclusions are drawn: 1) An excess of breaks occurs in the p arm of chromosome 12. 2) The distributions of breaks in the bands of chromosome 12 is significantly different from that expected on a random basis. 3) Translocations of chromosome 12 occur more often with chromosome 21 than any other chromosome, but these rearrangements do not involve a specific region of chromosome 12. 4) Most of the translocations were ascertained through their unbalanced meiotic products but seven translocations were "balanced". Of these "balanced" translocations, three individuals were abnormal and two were recurrent aborters. The concept that phenotypic outcome may be related to the gross structural characteristics of the translocation site is not supported in this study.