What is Turner syndrome (TS)?
Turner syndrome is a genetic disorder that affects only girls and women. X and Y chromosomes are responsible for determining the sex of an infant. In most cases, female infants have two X chromosomes. However, in female babies born with TS, one of the X chromosomes is missing or altered.
What are the signs of Turner syndrome?
One of the main features is growth failure. Girls with TS tend to grow more slowly than their peers during childhood and adolescence. The average height of adult women with TS is 4 feet 8 inches, unless they are treated with growth hormone. In that case, they may be several inches taller.
Problems with sexual development are another major feature of Turner syndrome. The ovaries of girls with TS either are small and fibrous or do not function normally. If the ovaries are present, they do not produce enough estrogen, so girls do not develop breasts or get menstrual periods. Most of girls with TS often do not go through puberty unless they receive hormone therapy. In some cases, if girls do go through puberty, menstrual irregularities occur or periods stop completely later on.
Some physical traits associated with Turner syndrome include:
- An unusually wide neck or webbed neck
- Low-set ears
- Low hairline at the back of the neck
- Small lower jaw
- Broad chest with nipples placed far apart
- Scoliosis (curvature of the spine)
- Narrow fingernails and toenails
- Arms that point out at the elbows
- Many moles on the skin
Other medical problems are associated with this condition. They include:
- Cardiovascular problems—About 30% of girls with TS have some structural defect of the heart. The most common problems are a bicuspid aortic valve and narrowing of the aorta (the main artery leaving the heart). High blood pressure (hypertension) may also be a problem. Enlargement of the aorta is rare, but it may be life-threatening unless it is quickly found and treated.
- Developmental delay and learning Disabilities—Overall intellectual function is normal but girls with Turner syndrome tend to have difficulties in visual motor and visual spacial skills.
- Osteoporosis—Women are more likely to have weak or thin bones due to a deficiency of estrogen. This may result in curvature of the spine, height loss and an increased chance of fractures.
- Ear problems—Malformation of the ears and middle ear infections are more common in girls with Turner syndrome. This can lead to hearing problems in later life.
- Kidney defects and urinary tract infections—About one-third of girls and women have malformed kidneys. The kidneys often function normally, but there may be a greater likelihood of urinary infections.
- Diabetes—There is an increased risk for type 2 diabetes.
- Thyroid problems—The most common condition is an underactive thyroid gland (hypothyroidism).
What causes Turner syndrome?
Turner syndrome occurs when one of the two X chromosomes that are typically present in the cells of females is missing or incomplete. Although TS is a genetic disorder, generally it is not inherited.
About 50% of girls and women with TS have a form of the disorder in which each cell only has one X chromosome instead of two. This type of TS is called monosomy X. It is caused by an error in the formation of reproductive cells (eggs or sperm) in one of the girl’s parents. During cell division, the egg or sperm may lose an X chromosome. This defect will be passed on when fertilization occurs.
In about 30% of all cases, girls or women have a pair of X chromosomes in some of the cells of the body, while other cells have only one X chromosome. This condition is called mosaic Turner syndrome or mosaicism.
Sometimes both X chromosomes are present, but one of them is genetically altered or has partial deletions. This occurs in about 20% of all cases.
In rare cases, TS may be inherited. This type of the syndrome is associated with an incomplete X chromosome.
How common is Turner syndrome?
Turner syndrome occurs in about 1 in every 2,500 female babies throughout the world.
How is Turner syndrome diagnosed?
Physical features such as short stature and other characteristics may be the first indication of Turner syndrome. Female infants with TS may show certain features soon after birth, such as swollen hands or feet, or webbing of the skin on the neck. Parents may notice that their girl has stopped growing or is much shorter than her peers. The lack of breast development or menstrual periods at the time when most girls are going through puberty are other signs. A genetic test called a karyotype analysis is needed to definitely diagnose TS. The test will determine whether one of the X chromosomes is missing or partially missing. A small sample of blood is required for the karyotype test.
Some women are not diagnosed with Turner syndrome until they reach adulthood. These women do go through puberty and have menstrual periods, but later on their periods cease or become irregular.
Turner syndrome may be diagnosed when an older pregnant woman undergoes prenatal genetic screening. A karyotype analysis may be performed on a sample of fluid removed during amniocentesis or chorionic villous sampling. However, the chance of having a baby with TS does not increase with the age of the mother. An ultrasound test may also show that a fetus has some physical features associated with TS, such as heart defects or the presence of lymph fluid around the neck.
How is Turner syndrome treated?
A girl with Turner syndrome should be evaluated and monitored by a pediatric endocrinologist, who can provide suggestions on treating hormone deficiencies. Parents should keep careful growth charts and be aware of other medical problems that may affect girls with TS.
- Human growth hormone--Girls with TS may be treated with synthetic human growth hormone injections to increase their height. The final height of girls who are treated with growth hormone may be increased by several inches, if treatment begins in early childhood.
- Androgens—Androgens are male hormones that are produced in boys and girls. The adrenal glands begin to produce androgens when girls are around 8 to 9 years old. The ovaries produce more androgens when girls go through puberty. These hormones cause the growth of hair under the arms and in the genital area and result in a growth spurt. A low dose of androgen along with growth hormone may increase growth in girls with TS without causing undesirable side effects, such as facial hair or acne. Androgens are not given to girls with TS until they are at least 9 years old.
- Hormone replacement therapy—In most cases, girls with TS require estrogen (a female hormone) to start developing breasts, normalize uterine size, and begin menstruating during puberty. The goal of estrogen replacement also is for better brain development, cardio-vascular function, and liver function.
- Girls and their parents should discuss when to begin estrogen therapy, because high estrogen replacement usually stops bone growth in the late teenage years. After girls who are taking estrogen begin to menstruate, progesterone is added to maintain their regular menstrual cycles.
- Women with Turner syndrome are usually infertile. However, sometimes they may be able to become pregnant via special fertilization techniques.
Hormone Health Network. Turner Syndrome. www.hormone.org
Turner Syndrome Society of the United States. Turner Syndrome: A Guide for Families.
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