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We report on a 16-year-old patient with Turner syndrome who presented a mos 46,X,del(X)(p22.1)⟦35〉/45,X⟦19〉/46,X,r(X)(p22.1q28) GTG-band karyotype. The R-banding showed that the abnormal X-chromosome was inactive in all 61 cells analyzed. Fluorescence in situ hybridization with a Xp/Yp subtelomeric probe revealed that both abnormal chromosomes lacked the complementary sequences, a fact consistent with a terminal deletion. Besides, the molecular analysis of the human androgen receptor gene showed that the rearranged chromosome was paternal in origin. Since the deleted and the ring chromosomes had the same size and banding pattern, and because the former was the predominant cell line, it was inferred that the Xp– formed a ring in some cells apparently without further loss of genetic material. However, the reverse sequence and even a simultaneous origin due to a complex intrachromosomal exchange are also conceivable. The mild Turner syndrome phenotype is explained by the mosaicism and by the size of the deleted segment. [Copyright &y& Elsevier]

A boy with Down syndrome due to a free trisomy 21 also had a metacentric Y chromosome with an arm euchromatic and the other heterochromatic inherited from his phenotypically normal father. This chromosome was mitotically stable and hybridized with the DYZ3 probe precisely at its primary constriction; in addition, a subtelomeric Xp/Yp probe gave the expected signal near the end of the euchromatic arm. So, the proband’s karyotype was 47,X,inv(Y)(p11q11.2),+21. Given the high frequency of both chromosome anomalies, we regard its concurrence as a mere coincidence. This observation, along with previous reports, allows us to classify the apparent pericentric inversions of the Y chromosome into two types: “true” inversions characterized by an alphoid single centromere and mitotic stability, and “false” inversions in which a nonalphoid centromere has taken over the usual alphoid centromere; indeed, these chromosomes are dicentric and mitotically unstable. Finally, the inv(Y) polymorphism in man compares with that documented in other mammal species, in which the rearranged Y chromosome neither impairs the fertility nor has other phenotypical consequences. [Copyright &y& Elsevier]