https://homosaurus.org/v3/homoit0000692 homoit0000692 Klinefelter syndrome 47XXY 2019-05-14 xsd:date 2021-12-08 xsd:date https://homosaurus.org/v3/homoit0000669 Intersex variations People with Klinefelter syndrome develop with an extra copy of the X chromosome, resulting in a 47XXY pattern (instead of the typical 46XY). These individuals might have smaller-than-typical testes that produce lower amounts of testosterone and/or sperm, and they may start puberty later than typical (or may not go through puberty without hormone therapy). They may grow taller than usual, may develop breast tissue, and often experience infertility. This variation often does not cause obvious physical differences, and many people do not realize they have it.