45, X/46, XYdic mosaicism in both skin and blood is reported in a six-year-old child presenting at birth with ambiguous genitalia. Examination revealed a greatly enlarged clitoris with perineal hypospadias, a small vagina, and bilateral inguinal hernias containing palpable gonads. Laparotomy and histology demonstrated a normal uterus and tubes with ovotestes in ovarian position. Physical examination was otherwise normal; she had the expected average height and weight for her age and no detectable aberrations of behavior. The dicentric Y chromosome was diagnosed on the basis of direct examination, autoradiography, and fluorescence analysis. Xg-blood grouping confirmed a single, maternally derived Xg locus. Search of suitable metaphases from short blood cultures revealed 104 cells with 46, XYdic; 26 with 45, X; 1 with 47, XYYdic; 2 with 46, XY; and 2 with 47, XYdicYdic. Findings in the skin indicated that the majority of cells were of the 45, X type. Examination of the patient’s blood cells during anaphase and telophase revealed more cells with bridge formation or lagging chromosomes than those from the normal controls. Such observation and the described karyotypes suggest that, although the dicentric Y usually divides normally during mitosis, in certain instances it divides abnormally to give XO and other aberrant cells. Possible mechanisms which may lead to such an unusual chromosome constitution are discusse
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