Chromosome Y-specific DNA in related human XX males

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Abstract
Human ‘XX males’ are sterile males whose chromosomes seem to be those of a normal female. About 1 in 20,000 males has a 46, XX karyotype, and most cases are sporadic, that is, they are without familial clustering1. It has long been argued that maleness in XX males may result from the undetected presence of a small, testis-determining fragment of the Y chromosome2, and there is strong evidence for this in sporadically occurring XX males3–5. Indeed, the genomes of three of four sporadic XX males tested were found to contain certain Y-specific DNA sequences6. A pedigree in which three XX males occur has been interpreted as being consistent with autosomal recessive inheritance of maleness7,8, and it has been argued that the basis of XX maleness in this family is fundamentally different from that in the sporadic cases9. However, we report here that these related XX males, like the sporadic cases, contain portions of the Y chromosome. The portion of the Y chromosome present in one of the three XX males differs from that present in the other two.