The Scientific background

In 1942 Dr Harry Klinefelter and his co-workers published a study about nine men who had enlarged breasts, sparse facial & body hair & small, firm, infertile testes.

By the late 1950s other researchers discovered that men with Klinefelter's Syndrome had an extra sex chromosome giving 47XXY instead of the more usual 46XY.

Based on studies in the US in the 1970s it is clear that KS is one of the commonest genetic abnormalities known; 1 in 500 to 1 in 1000 live births.

Women usually inherit two X chromosomes; one from each parent.

Men inherit an X from their mothers and a Y from their fathers.

However the meiosis that occurs in the cells destined to become eggs & sperm occasionally gives rise to an egg with two Xs or a sperm with both an X and a Y.

There are two chances to produce an XXY male. Either an XY sperm fertilises an X egg or a Y sperm fertilises an XX egg.

There are other less common variations; for example 48XXXY or 49XXXXY. There is also a mosaic type where some body cells are 46XY & other cells are 47XXY.

Physical Characteristics

Klinefelter's Cat?

Frequently Asked Questions