Henry Klinefelter - Klinefelter Syndrome

In 1942, Henry Klinefelter published a report on 9 men who had enlarged breasts, sparse facial and body hair, small testes, and an inability to produce sperm. Klinefelter syndrome is named after Dr. Henry Klinefelter, who first described a group of symptoms found in the above mentioned men with the extra X chromosome.

Klinefelter syndrome, also known as the XXY condition, is a term used to describe males who have an extra X chromosome in most of their cells. Instead of having the usual XY chromosome pattern that most males have, these men have an XXY pattern. In 1959, these men with Klinefelter syndrome were discovered to have an extra sex chromosome (genotype XXY) instead of the usual male sex complement (genotype XY).

Klinefelter syndrome is the most common chromosomal disorder associated with male hypogonadism and infertility. It is defined classically by a 47,XXY karyotype with variants that demonstrate additional X and Y chromosomes.

The syndrome is characterized by hypogonadism (small testes, azoospermia, oligospermia), gynecomastia in late puberty, psychosocial problems, hyalinization and fibrosis of the seminiferous tubules, and elevated urinary gonadotropin levels.

Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The two sex chromosomes determine if you become a boy or a girl. Females normally have two of the same sex chromosomes, written as XX. Males normally have an X and a Y chromosome (written as XY).

Klinefelter syndrome is found in about 1 out of every 500 - 1,000 newborn males. Women who have pregnancies after age 35 are slightly more likely to have a boy with this syndrome than younger women.

Even though all men with Klinefelter syndrome have the extra X chromosome, not every XXY male has all of those symptoms.

Because not every male with an XXY pattern has all the symptoms of Klinefelter syndrome, it is common to use the term XXY male to describe these men, or XXY condition to describe the symptoms.

Scientists believe the XXY condition is one of the most common chromosome abnormalities in humans. About one of every 500 males has an extra X chromosome, but many don't have any symptoms.

What are the symptoms of the XXY condition?

Not all males with the condition have the same symptoms or to the same degree. Symptoms depend on how many XXY cells a man has, how much testosterone is in his body, and his age when the condition is diagnosed. The XXY condition can affect three main areas of development 1) physical, 2) language, and 3) social.

Physical development

As babies, many XXY males have weak muscles and reduced strength. They may sit up, crawl, and walk later than other infants. After about age four, XXY males tend to be taller and may have less muscle control and coordination than other boys their age.

As XXY males enter puberty, they often don't make as much testosterone as other boys. This can lead to a taller, less muscular body, less facial and body hair, and broader hips than other boys. As teens, XXY males may have larger breasts, weaker bones, and a lower energy level than other boys.

By adulthood, XXY males look similar