An XXXY boy with X/XY half-sister.

The clinical findings in a 13-year-old 48,XXXY boy are described. His half-sister (same mother) has a 45,X/XY karyotype. The Xga blood studies are compatible with his extra X's originating from the mother. These Xga studies and the IgM levels in the 48,XXXY boy raise the possibility of a gene-dosage effect for X-linked genes affecting these traits. The proband also has chronic pulmonary problems, an interesting association that has been noted with the Klinefelter syndrome, usually in adults.