Body Composition in Infants With Klinefelter Syndrome and Effects of Testosterone Treatment

Body Composition in Infants With Klinefelter Syndrome and Effects of Testosterone Treatment

This research study in infant males with Klinefelter syndrome (47,XXY) will learn more about body composition (muscle and fat) and male hormones and look at the effect of testosterone shots on body composition. The Investigators know that older boys and men with Klinefelter syndrome often have more fat compared to muscle than adults without Klinefelter syndrome, but we do not know if this difference is present at birth or develops over time. The Investigators will learn if body composition and motor skills are improved with testosterone treatment in infants with Klinefelter syndrome.

Inclusion Criteria:

• Male infants with 47,XXY karyotype

Exclusion Criteria:

• Gestational age at birth <36 weeks
• Birth weight <5%ile or >95% for gestational age
• History of thrombosis in a first degree relative
• Exposure to androgen therapy outside of the study protocol.