Early androgen deficiency in infants and young boys with 47,XXY Klinefelter syndrome.

Background/aims: Klinefelter syndrome (KS) is characterized by the karyotype 47,XXY. In this study, we evaluated the physical and testicular failure phenotypes of infants and young boys with KS.

Methods: The evaluation included auxologic measurements, biologic indices of testicular function, and clinical assessment of muscle tone in 22 infants and young boys with KS, ages 1-23 months.

Results: Mean length, weight, and head circumference in SDS were generally within the normal range at -0.3 +/- 1.0, -0.1 +/- 1.4, and 0.0 +/- 1.5, respectively. Mean penile length and testicular volume SDS were -0.9 +/- 0.8 and -1.1 +/- 0.8, indicating significantly reduced penile and testicular size. Mean testosterone levels for the boys < or =6 and >6-23 months were 128 +/- 131 (4.4 +/- 4.5 nmol/l) and 9.5 +/- 7.2 ng/dl (0.3 +/- 0.2 nmol/l), respectively. High-arched palate was observed in 6/17 boys and clinodactyly (5th finger) was observed in 15/16 boys. Hypotonia was evaluated clinically and was noted to be present in 12/17 boys.

Conclusion: The physical phenotype in infants and young boys with KS (1-23 months old) includes normal auxologic measurements and early evidence of testicular failure. Muscle tone was decreased in most of the boys. Testicular volume and penile length were diminished, indicating early androgen deficiency. The neonatal surge in testosterone was attenuated in our KS population. Thus, infants and young boys with KS have evidence of early testicular failure. The etiology of this failure and the clinical role of early androgen replacement require further study.