Turner syndrome is a human genetic abnormality , caused by a nondisjunction in the Censored page that occur to females (1 out of every 2,500 births). Instead of the normal XX or XY sex chromosomes, only one X chromosome is present and fully functional. In Turner syndrome, female sexual characteristics are present but underdeveloped. Common symptoms of Turner syndrome include:
- Short stature
- Lymphoedema (swelling) of the hands and feet
- Broad chest and widely-spaced nipples
- Low hairline
- Low-set ears
Other symptoms include a small lower jaw, cubitus valgus (turned-out elbows), a webbed neck, and soft, upturned nails. Less common are pigmented moles, hearing loss, and a high-arch palate. Turner syndrome manifests itself differently in differently people, and no two women need share the same symptoms.
Turner syndrome is caused by the loss of genetic material from one of the sex chromosomes. In Turner syndrome, the embryo has only one functioning sex chromosome. This chromosome is always an X chromosome, as an embryo with only a Y chromosome is incapable of survival. The remaining X chromosome is either absent or damaged. Mosaic Turner syndrome, where some of the cells have two sex chromosomes but others have only a single functioning X chromosome, is also possible. In cases of mosaic Turner syndrome, the symptoms are usually less pronounced.
There are no known risk factors for Turner syndrome.
Approximately 98% of all fetuses with Turner syndrome spontaneously abort. Fetuses with Turner syndrome make up about 10% of the total number of spontaneously aborted fetuses in the United States. The incidence of Turner syndrome in live births is between 1 in 2,500 and 1 in 3,000.
Turner syndrome may be diagnosed by an amniocentesis during pregnancy. Sometimes, fetuses with Turner syndrome are identified by abnormal ultrasound findings (i.e. heart defect, kidney abnormality, cystic hygroma, ascities). Although the recurrence risk is not increased, genetic counseling is often recommended for families who have had a pregnancy or child with Turner syndrome.
The syndrome is named after Henry Turner , an Oklahoma endocrinologist, who described it in the 1940s. In Europe, it is often called Ullrich-Turner syndrome or even Bonnevie-Ulrich-Turner syndrome to acknowledge that earlier cases had also been described by European doctors.
Medical consequences of Turner syndrome
While most of the side effects of Turner syndrome are harmless, some can lead to significant medical problems.
Between 5% and 10% of those born with Turner syndrome have coarctation of the aorta, a condition which if untreated causes blood to flow in a thin, fast stream against the side of the heart. This can lead to heart rupture. Coarctation of the aorta can be corrected surgically as soon as it is detected.
Up to 15% of adults with Turner syndrome have bicuspid aortic valves, meaning that there are only two, instead of three, parts to the valves in the main blood vessel leading from the heart. Because bicuspid valves are capable of regulating blood flow properly, this condition may go undetected without regular screening. Because bicuspid valves must work harder than ordinary heart valves, they are more likely to deteriorate and later fail.
Turner syndrome is often associated with persistent hypertension, sometimes even in childhood. In the majority of Turner syndrome patients with hypertension, there is no specific cause. In the remainder, it is usually associated with heart or kidney abnormalities.
Normal skeletal development is inhibited due to a large variety of factors, mostly hormonal. The head, neck, and chest of women with Turner syndrome are usually of normal size, but the arms and legs are unusually short. The average height of a woman with Turner syndrome is 4'7", or about 140cm.
The fourth metacarpal bone (fourth toe and ring finger) may be unusually short.
Due to inadequate circulation of estrogen, many of those with Turner syndrome develop osteoporosis. This can decrease height further, as well as exacerbate the curvature of the spine, possibly leading to scoliosis. It is also associated with an increased risk of bone fractures.
Approximately one-third of all women with Turner syndrome have one of three kidney abnormalities:
- A single, horseshoe-shaped kidney on one side of the body, and no kidney on the other side.
- An abnormal urine-collecting system.
- Poor blood flow to the kidneys.
Some of these conditions can be corrected surgically. Even with these abnormalities, the kidneys of most women with Turner syndrome function normally. However, as noted above, kidney problems may be associated with hypertension.
Approximately one-third of all women with Turner syndrome have a thyroid disorder. Usually it is hypothyroidism, specifically Hashimoto's thyroiditis. If detected, it can be easily treated with thyroid hormone supplements.
Women with Turner syndrome are at a moderately increased risk of developing type 1 diabetes in childhood and a substantially increased risk of developing type 2 diabetes by adult years.
Turner syndrome does not cause mental retardation or impair cognition. However, women with Turner syndrome may have a specific difficulty perceiving spatial relationships. This may also manifest itself as difficulty with motor control or with mathematics. While it is non-correctable, in most cases it does not cause difficulty in daily living.
Women with Turner syndrome are almost universally infertile. While there are cases of women with Turner syndrome becoming pregnant, they are very rare. Usually hormone replacement is used to spur growth of secondary sexual characterics at the time when puberty should onset.
What can be done?
As a chromosomal condition, there is no "cure" for Turner syndrome. However much can be done to minimize the symptoms. For example:
Estrogen replacement therapy has been used since the condition was described in 1938 to promote development of secondary sexual characteristics. Estrogens are also important for maintaining good tissue and bone integrity.
- Modern reproductive technologies have also been used to help women with Turner syndrome become pregnant if they desire. For example, a donor egg can be used to create an embryo, which is carried by the Turner syndrome woman.
Last updated: 02-10-2005 05:58:19
Last updated: 04-25-2005 03:06:01