To test the hypothesis that H-Y antigen (present on both somatic and germ cells in normal males but not normal females) is essential for testicular differentiation, we studied four XX males and three XX true hermaphrodites. Blood cells from six subjects and cultured gonadal fibroblasts from a seventh expressed H-Y antigen. Since expression of this antigen requires the presence of a gene normally carried by the Y chromosome, this gene, and perhaps additional Y chromosomal material, should have been present in the genome of these subjects. In one patient this presence is accounted for by a Y-to-X translocation, detectable by chromosome banding. In another a normal Y chromosome was present in a minor population of cells. In the remaining five, no karyotypic abnormality was detectable. Immunologic detection of H-Y antigen is a sensitive test for the presence of the Y chromosome or of its male-determining segment.
Flattened metaphase figures were obtained by squashing or air-drying cells from human leucocyte cultures that had been treated with colchicine and hypotonic sodium citrate prior to fixation. In such metaphase figures the Y chromosome was at the periphery of the figure more often than chance expectation and more often than the chromosome pairs 1, 2, or 16 or the chromosome groups 13–15, 17–18, 19–20, or 21–22. The Y chromosome was further from the center of circular metaphase figures than the mean value of all the chromosomes or the chromosome pairs 1, 2, or 3 or the chromosome groups 4–5, 6–12+X, 19–20 or 21–22.
To determine whether the gene that controls the expression of H-Y ("male") antigen on human cells is Y-linked, we have compared the H-Y antigen level in normal males with that in three males with two Y chromosomes. Leukocytes from one XXYY and two XYY males express more H-Y antigen than leukocytes from normal XY males. We conclude that a structural gene or positive regulatory gene for H-Y antigen is on the human Y chromosome. Testing for the H-Y antigen may be of benefit in patients who have signs of masculinization but who lack an identifiable Y chromosome. Positive results for the H-Y antigen would be tentative evidence that the corresponding region of the Y chromosome was present, perhaps as part of a translocation, despite the absence of a typical Y chromosome.
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