Testicular size and shape of 47,XYY and 47,XXY men in a double-blind, double-matched population survey

This paper reports the testicular size and shape of 12 men with 47,XYY, 14 men with 47,XXY, and 52 matched controls with 46,XY. The abnormal karyotypes were identified in a systematic population search for XYY and XXY men. The subjects and their matched controls were examined in a double-blind fashion. The testes of the XYY men showed no significant differences from those of their XY controls for volume or shape. This indicates that previous reports of abnormal testes in XYYs reflect selection and publication bias and do not provide an accurate description of the condition of 47,XYY men's testicles. As expected, the testes of the XXY men were significantly smaller than those of their XY controls, and there was also a difference in shape. However, the mean size in this sample of XXYs was larger than in previous reports on Klinefelter syndrome patients, indicating that previous reports on XXYs, identified in clinics for male hypogonadism and other institutions, also suffered from selection bias.