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What is Klinefelter syndrome?

Dr. Jeanne Morrison, PhD
Family Practitioner

Klinefelter’s syndrome is a genetic disorder found in males and affects male sexual development. Males normally have a total of 46 chromosomes; one X and one Y chromosome (46-XY). However, males with Klinefelter’s syndrome have an extra X chromosome (47-XXY) and therefore a total of 47 chromosomes.

The presence of an extra X chromosome primarily affects the testes.  Males with this condition typically have small testes that do not produce enough testosterone, which is the hormone that directs male sexual development before birth and during puberty. A shortage of testosterone during puberty can lead to breast enlargement (gynecomastia), reduced facial and body hair, and an inability to father children (infertility). Older children and adults with Klinefelter's syndrome tend to be taller than other males their age. Compared with other men, adult males with Klinefelter's syndrome have an increased risk of developing breast cancer and chronic inflammatory diseases such as systemic lupus erythematosus. Their chance of developing these disorders is similar to that of normal adult females.  Boys with Klinefelter's syndrome may have learning disabilities and difficulty with speech and language development.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.