Non-fluorescent Y chromosome in a male infant with Turner's symptoms and XO/XY mosaicism.

A 45, X/46,XY mosaicism was found in a male infant with stigmata of Turner's syndrome but normal male external genitalia. In contrast to the Y chromosome of his father, the Y chromosome of the patient does not display either the characteristic brilliant fluorescence or the typical dark heterochromatin staining of the distal long arm. Furthermore, DNA replication in the abnormal Y chromosome was shown to be premature. Mechanisms leading to the observed abnormalities are discussed.