title: The origin of 45,X males.
abstract: Maleness in association with the karyotype 45,X is a very rare and hitherto unexplained condition previously described in only four or five patients. This study was carried out to determine whether such males might actually possess Y-chromosomal material. Of the two 45,X males studied, one was found to be a low-grade mosaic with a 46,XY karyotype in less than 3% of fibroblasts; all lymphocytes karyotyped were 45,X. Fibroblast DNA from this individual was found to contain Y-specific repeated sequences in 1%-3% the amount observed in the father, consistent with mosaicism for a 46,XY cell line. No Y-specific repeated sequences were detected in the other patient, in whom all mitoses were 45,X. In neither patient were there detectable amounts of any of the single-copy Y-specific DNA sequences for which we tested. Studies of Xg blood groups and of X-linked restriction fragment length polymorphisms indicated that the single X chromosome was of maternal origin in both 45,X male probands. In contrast to the situation in XX males, we can exclude paternal X-Y interchange as the etiology in the cases described here. Our findings are compatible with mosaicism being the explanation of at least some "45,X" males.
mesh_terms: D004262:DNA Restriction Enzymes; D005819:Genetic Markers; D006801:Humans; D007223:Infant; D007621:Karyotyping; D008297:Male; D008957:Models, Genetic; D009030:Mosaicism; D009634:Noonan Syndrome / Q000235:genetics*; D009693:Nucleic Acid Hybridization; D011110:Polymorphism, Genetic; D012732:Sex Determination Analysis; D014960:X Chromosome; D014998:Y Chromosome
chemical_list: D005819:Genetic Markers; D004262:DNA Restriction Enzymes