Kleinfelter syndrome. Light micrograph of a karyotype (set of chromosomes) from a man with Kleinfelter syndrome. This congenital syndrome is characterised by the presence of an extra female (X) sex chromosome. The normal male karyotype for sex chromosomes is XY, but those with Kleinfelter have an XXY karyotype. Men with the syndrome may be tall, have a more female (pear) body shape, develop breasts (gynaecomastia), have sparse facial and body hair and have some language impairment. All those affected are also sterile. Some of the symptoms can be treated with testosterone injections and gynaecomastia can be treated with surgery.