DiGeorge syndrome

Definition

Klinfelter syndrome is a genetic disorder affecting males. People with this syndrome are born with at least one extra X chromosome.

Description

Chromosomes are found in every cell in the body. Chromosomes contain genes, structures that direct the growth and functioning of all the cells and systems in the body. In other words, chromosomes are responsible for passing on hereditary traits from parents to child, like eye color, height, nose shape, etc. Chromosomes also determine whether the child will be male or female. Normally, a person has a total of 46 chromosomes in each cell, two of which are responsible for determining that individual's sex. These two sex chromosomes are called X and Y. The combination of these two types of chromosomes determines the sex of a child. Females have two X chromosomes (the XX combination); males have one X and one Y chromosome (the XY combination).

In Klinefelter syndrome, a problem very early in development results in an abnormal number and arrangement of chromosomes. Most commonly, a male with Klinefelter syndrome will be born with 47 chromosomes in each cell, rather than the normal number of 46. The extra chromosome is an X chromosome. This means that rather than having the normal XY combination, the male has an XXY combination. Some Klinefelter patients have more complex chromosomal errors, including the presence of 48, 49, or even 50 chromosomes. All of the extra chromosomes are Xs.

Klinefelter syndrome is one of the most common chromosomal abnormalities. About 1 in every 1,000 infant boy is born with some variation of this disorder.

Causes & symptoms

The cause of Klinefelter syndrome is unknown, although it has been noted that the disorder is seen more frequently among the children of older mothers.

The presence of more than one X chromosome in a male results in a delay in puberty. The testicles and the penis tend to be smaller than normal, and infertility is common. The testicles may remain up in the abdomen, instead of descending into the scrotum as is normal. Body hair decreases and breast size increases. Sexual drive is often below normal. Boys with Klinefelter syndrome tend to be tall and thin.

While it was once believed that all boys with Klinefelter syndrome were mentally retarded, doctors now know that the disorder can exist without retardation. However, children with Klinefelter syndrome frequently have difficulty with language, including learning to speak, read, and write. Some children have difficulty with social skills and tend to be more shy, anxious, or immature than their peers. Overly aggressive behavior has also been noted.

The greater the number of X chromosomes present, the greater the disability. Boys with several extra X chromosomes have distinctive facial features, more severe retardation, deformities of bony structures, and even more disordered development of male features.

Diagnosis

Diagnosis of Klinefelter syndrome is made by examining chromosomes for evidence of more than one X chromosome present in a male. Other abnormalities of sex hormones are common, including a low level of the male hormone testosterone.

Treatment

There is no treatment available to change chromosomal makeup. However, delayed puberty and decreased sexual drive can both be treated with injections of a testosterone preparation about every three weeks.

Prognosis

While many men with Klinefelter syndrome go on to live normal lives, nearly 100% of these men will be sterile (unable to produce a child). Because men with Klinefelter syndrome have enlarged breasts, they have nearly the same chance of developing breast cancer as do women. Lung disease and certain rare tumors are also increased in patients with Klinefelter syndrome.

Key Terms

Chromosomes

Spaghetti-like structures located within the nucleus (or central portion) of each cell. Chromosomes contain the genetic information necessary to direct the development and functioning of all cells and systems in the body.

Further Reading

For Your Information

Books

• DiGeorge, Angelo M. "Klinefelter Syndrome." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.

  Periodicals

• Sotos, Juan F. "Genetic Disorders Associated with Overgrowth." Clinical Pediatrics, 36 (1)(January 1997): 39+.

Gale Encyclopedia of Medicine. Gale Research, 1999.