Klinefelter Syndrome

Klinefelter Syndrome

Klinefelter Syndrome (KS) is a birth defect in which males are born with at least one extra sex chromosome. In 1942, certain physical characteristics, abnormal in adult males, were first identified by Dr. Harry Finch Klinefelter, Jr. and two colleagues. These characteristics were abnormally small testes and fatty breast tissue. Detailed chromosome studies conducted years later resulted in the discovery that males with these characteristics have an extra sex chromosome


American Association for Klinefelter Syndrome Information and Support (AAKSIS)

AAKSIS (pronounced “access”)
AAKSIS is dedicated to bringing you accurate and current information about Klinefelter Syndrome and is a network for individuals, families, and anyone interesting in learning more about Klinefelter Syndrome.
3796 Ogden Lane
Mundeline, IL 60060
Phone: 888 466-5747


Resources to help you better understand your child and get the support you need to help guide them to maturity and their fullest potential.
P.O. Box 659
Paoli, PA 19301
Phone: 888-999-9428
Email: info@genetic.org
Research Opportunities for Families

Klinefelter Syndrome Information and Support

Living with Klinefelter Syndrome, links to other organizations, support groups and resources.
* Steps for Starting a Support Group

Other Information:

Kleinfelter Syndrome –  Genetics Home Reference US National Library of Medicine

Klinefelter Syndrome – National Institute of Health

Kleinfelter Syndrome – Genetic and Rare Disease Information Center

About Klinefelter Syndrome – National Human Genome Research Institute

Fact Sheet last updated on: 3/21/2023


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