Only affects boys, due to an extra X chromosome

Rarely people with Klinefelter syndrome can have even more X chromosomes, such as 48 XXXY or 49 XXXXY. This is associated with more severe features.

Epidemiology

1 in 600 male births

Usually presents in adolescence - Males have an extra female hormone so can undergo hormonal linked changes

up to 75% of males are never diagnosed

Clinical features

Usually patients with Kleinfelter syndrome appear as normal males until puberty. At puberty can develop features suggestive of the condition:

• Taller height
• Wider hips
• Gynaecomastia
• lack of secondary sexual charecteristicas
• Weaker muscles
• Small testicles
• Reduced libido
• Shyness
• Infertility
• Subtle learning difficulties (particularly affecting speech and language)