Klinefelter syndrome

The XXY karyotype of Klinefelter syndrome occurs with an
incidence of 1 in 600 liveborn males. It arises by
nondisjunction and the additional X chromosome is equally
likely to be maternally or paternally derived. There is no
increased early pregnancy loss associated with this karyotype.
Many cases are never diagnosed. The primary feature of the
syndrome is hypogonadism. Pubertal development usually
starts spontaneously, but testicular size decreases from
mid-puberty and hypogonadism develops. Testosterone
replacement is usually required and affected males are infertile.
Poor facial hair growth is an almost constant finding. Tall
stature is usual and gynaecomastia may occur. The risk of
cancer of the breast is increased compared to XY males.
Intelligence is generally within the normal range but may be
10–15 points lower than siblings. Educational difficultes are
fairly common and behavioural disturbances are likely to be
associated with exposure to stressful environments. Shyness,
immaturity and frustration tend to improve with testosterone
replacement therapy.