40 XO/49 XYYYY mosaicism in a male with stigmata of Turner's syndrome.

A male subject with Turner-like stigmata and chromosomic constitution 45,XO (97.5%) and 49,XYYYY (1.1%) is reported. The findings of a low percentage line bearing Y chromosome in a patient with clinical features similar to those described for XO males, would support the hypothesis that masculinization in certain individuals with 45,XO karyotype may be due to an undetected mosaicism.