A 5‐month‐old girl had a typical 12p trisomy syndrome due to a monocentric i(12p) present in a 46‐chromosome complement that also included the translocation of all 12q onto the 8p telomere; i.e., her complex karyotype could be written as 46.XX, – 8,–12,+ der(8),t(8;12)(p23.3;cen), + i(12p). The present concurrence of a whole‐arm q translocation and an i(p) for a single chromocome, along with six previous similar instances involving chromosomes 4, 5 and 9, suggests the following origin for such a special rearrangement: a centric fission in Gl initially yielding two telocentrics; at the next replication, the tel(q) translocates onto a nonhomologous telomere (centromere‐telomere fusion), whereas the tel(p) becomes an i(p). This mechanism can be either meiotic or postzygotic and surmises that the translocated long arm retains a partial centromere, which subsequently is inactivated and loses its staining properties.
A t(X;3) (q26;q13.2) was found in three generations of a family. Female carriers exhibited normal reproductive function, whereas all three postpuberal male carriers showed spermatogenesis arrest at meiosis I. Additionally, a 2 3/12-year-old girl had duplication 3qter resulting from an adjacent-1 segregation.
A 19‐year‐old female patient with gonadal dysgenesis and a de novo t(X;17) (Xp17q;Xq17p) is described. Since the critical segment Xq13 → q26 was intact, this case is a further exception to the critical region hypothesis.
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