Klinefelter syndrome Health Article

Definition

Klinefelter syndrome is the presence of an extra X chromosome in a male.

Alternative Names

47 X-X-Y syndrome

Causes, incidence, and risk factors

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 one of a group of sex chromosome problems. It results in males who have at least one extra X chromosome. Usually, this occurs due to one extra X (written as XXY).

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.

Symptoms

The most common symptom is infertility. Other symptoms may include:

• Abnormal body proportions (long legs, short trunk, shoulder equal to hip size)
• Enlarged breasts (gynecomastia)
• Sexual problems
• Less than normal amount of pubic, armpit, and facial hair
• Small, firm testicles
• Small penis
• Tall height

Signs and tests

Adults may come to the doctor because of infertility. School-age children may be brought in to because of learning problems.

The following tests may be performed:

• Karyotyping
• Semen count
• Serum estradiol levels (a type of estrogen)
• Serum follicle stimulating hormone
• Serum luteinizing hormone
• Serum testosterone