Turner syndrome is a genetic condition in which a female has only one complete X sex chromosome. Chromosomes are the carriers of inheritance, and sex chromosomes help determine an individual’s sex. Human beings normally have two sex chromosomes, with females having two X chromosomes (typically written XX) and males having one X and one Y chromosome (XY). Females with Turner syndrome have one X chromosome that is either incomplete or missing entirely (typically written 45, X). Symptoms of the condition vary for each individual, but typically include incomplete growth and sexual development and other physical abnormalities. Turner syndrome occurs in about 1 of every 2,000 female births. The syndrome is named for Henry Turner, the American physician who first described it in a medical journal in 1938.
Turner syndrome is not inherited. It results from a mistake that occurs after fertilization during cell division, causing one X chromosome to be completely lost or significantly damaging it. Turner syndrome is an example of aneuploidy—the condition of having an abnormal number of chromosomes.
Medical experts diagnose Turner syndrome by organizing images of the individual’s chromosomes into a profile called a karyotype. A karyotype can be prepared before birth through a procedure called amniocentesis (see Amniocentesis ).
At birth, girls with Turner syndrome may have hands and feet that appear swollen or puffy along with extra folds of skin along the neck, called a webbed neck. Heart and blood vessel defects occur in some girls born with Turner syndrome. Kidney defects are also common. Other physical symptoms include short stature, a low hairline at the back of the neck, low-set ears, widely spaced nipples, nails that slant upward, and arms that appear turned outward from the elbow.
Girls with Turner syndrome usually have an intelligence within the normal range. Some of them may have learning difficulties, particularly problems with mathematics and with spatial ability tasks, such as distinguishing between left and right. Spatial ability involves the visualization of objects in the mind.
At puberty, most females with Turner syndrome do not develop secondary sexual characteristics—that is, physical traits, such as body shape and breast development, associated with the onset of sexual maturity. Most women with Turner syndrome do not have functioning ovaries, do not menstruate, and are infertile. They are also at greater risk of developing diabetes, osteoporosis, thyroid disorders, high blood pressure, and obesity.
Treatment for Turner syndrome includes hormone replacement therapy. Physicians may use injections of human growth hormone (hGH), the main hormone that regulates human growth and development, to help girls with Turner syndrome achieve a more normal stature. Estrogen, a hormone that stimulates sexual development in females, can be administered during puberty to help them develop secondary sex characteristics. Girls with Turner syndrome and their families often benefit from participation in support groups and from genetic counseling (see Genetic counseling ).
See also Aneuploidy .
