A patient with a mitotically unstable dic(Y)(pll) chromosome is reported. Physical examination revealed a small penis with severe hypospadia, undescended testes, rudimentary vagina, uterus, left fallopian tube, and no stigmata of Turner syndrome. Longitudinal chromosome studies over a four-year period, including blood, skin, foreskin, and testicular tissue, revealed 45, X/46, X, dic(Y)(pll)/46, X, del(dicY) mosaicism. The proportions of these cells varied in the different tissues, and only 45, X and 46, X, del(dicY) were major cell lines in testicular tissue. Additional minor cell lines were present mainly in peripheral blood: 47, X, dicY, dicY; 47, X, dicY, del (dicY); and 47, X, del(dicY), del(dicY). Premature disjunction of one of the centromeres in a high percentage of the dicentric Y chromosomes in metaphase was observed by Q- and C-banding. Lymphocytes at anaphase and telophase showed lagging Y chromosomes, fragments, and nondisjunction. These observations indicate a high degree of mitotic instability and thus raise the question of the effect of premature centromeric disjunction on mitotic instability of dicentric chromosomes.
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