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 X g a blood studies are compatible with his extra X's originating from the mother. These X g a 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, although usually in adults.