Klinefelter syndrome: what every paediatrician needs to know

Klinefelter syndrome (KS) is a common sex chromosome variation around one in 750 live male births. The karyotype is usually 47,XXY. However, three quarters of KS males are never identified. Lifespan is not reduced. There is no specific infant phenotype. Prepubertal growth is generally rapid and children may become taller than the mid-parental height. Adolescent growth is not increased, so extreme tall stature is unusual. Overweight and central obesity occur in some boys from mid-childhood. Infant development is usually within age related ranges, although one third may need speech support and two thirds reading and language support. IQ is within the population range.

Puberty onset is not delayed and testosterone levels increase typically at first but often fail to rise in late puberty and biochemical hypogonadism is diagnosed by a low morning testosterone concentration. Clinical hypogonadism is common with central obesity, gynaecomastia and low muscle development and strength. Testosterone supplementation with transdermal gel or injections may help to improve physical development and functioning. Sperm production is severely reduced resulting in azoospermia in the majority. Fertility counselling is important but assessment not needed until late adolescence when surgical testicular sperm extraction can be performed, with no advantage at younger ages.