A condition affecting males that is caused by the presence of extra X chromosomes.

Klinefelter's syndrome, also known as primary micro-orchidism, affects males only. A normal male has one pair of sex chromosomes made up of one X and one Y. In Klinefelter's syndrome, one or more extra X chromosomes are present. (The extra chromosomes identified as Klinefelter's syndrome fall into one of the following categories: 47XXY, 48XXYY, 48XXXY, 49XXXY, or 49 XX/XXY.

Although individuals with Klinefelter's syndrome appear to be more likely to experience learning difficulties, the syndrome often remains undiagnosed. At puberty, a boy with more than one extra X chromosome may tend to develop enlarged breasts, a condition that can be treated with medication. In addition, the testes remain very small, and most males with Klinefelter's syndrome produce little or no sperm. In fact, it is during tests for infertility that Klinefelter's is most frequently diagnosed.

For Further Study

Books

Berch, Daniel B., and Bruce G. Bender. Sex Chromosome Abnormalities and Human Behavior: Psychological Studies. Boulder: Westview Press, 1990.

Strom, Charles. Heredity and Ability: How Genetics Affects Your Child and What You Can Do About It. New York: Plenum Press, 1990.

Therman, Eeva. Human Chromosomes: Structure, Behavior, and Effects. New York: Springer-Verlag, 1993.