Turner syndrome

A gonadal dysgenesis syndrome occurring in phenotypic females, characterized by the absence of a part or all of one of the sex chromosomes. Signs and symptoms include short stature, webbing of neck, low-set ears, hypogonadism, and sterility.

Neck of girl with Turner Syndrome

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Turner syndrome features

The most common feature of Turner syndrome is short stature, which becomes evident by about age 5. An early loss of ovarian function (ovarian hypofunction or premature ovarian failure) is also very common. The ovaries develop normally at first, but egg cells (oocytes) usually die prematurely and most ovarian tissue degenerates before birth. Many affected girls do not undergo puberty unless they receive hormone therapy, and most are unable to conceive (infertile). A small percentage of females with Turner syndrome retain normal ovarian function through young adulthood.

About 30 percent of females with Turner syndrome have extra folds of skin on the neck (webbedneck), a low hairline at the back of the neck, puffiness or swelling (lymphedema) of the hands and feet, skeletal abnormalities, or kidney problems. One third to one half of individuals with Turner syndrome are born with a heart defect, such as a narrowing of the large artery leaving the heart (coarctation of the aorta) or abnormalities of the valve that connects the aorta with the heart (the aortic valve). Complications associated with these heart defects can be life-threatening.

Most girls and women with Turner syndrome have normal intelligence. Developmental delays, nonverbal learning disabilities, and behavioral problems are possible, although these characteristics vary among affected individuals.

Epidemiology

This condition occurs in about 1 in 2,500 newborn girls worldwide, but it is much more common among pregnancies that do not survive to term (miscarriages and stillbirths).

Causes

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Turner syndrome is related to the X chromosome, which is one of the two sex chromosomes. People typically have two sex chromosomes in each cell: females have two X chromosomes, while males have one X chromosome and one Y chromosome. Turner syndrome results when one normal X chromosome is present in a female's cells and the other sex chromosome is missing or structurally altered. The missing genetic material affects development before and after birth.

About half of individuals with Turner syndrome have monosomy X, which means each cell in the individual's body has only one copy of the X chromosome instead of the usual two sex chromosomes. Turner syndrome can also occur if one of the sex chromosomes is partially missing or rearranged rather than completely absent. Some women with Turner syndrome have a chromosomal change in only some of their cells, which is known as mosaicism. Women with Turner syndrome caused by X chromosome mosaicism are said to have mosaic Turner syndrome.

Researchers have not determined which genes on the X chromosome are associated with most of the features of Turner syndrome. They have, however, identified one gene called SHOX that is important for bone development and growth. The loss of one copy of this gene likely causes short stature and skeletal abnormalities in women with Turner syndrome.

Inheritance

Most cases of Turner syndrome are not inherited. When this condition results from monosomy X, the chromosomal abnormality occurs as a random event during the formation of reproductive cells (eggs and sperm) in the affected person's parent. An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes. For example, an egg or sperm cell may lose a sex chromosome as a result of nondisjunction. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have a single X chromosome in each cell and will be missing the other sex chromosome.

Mosaic Turner syndrome is also not inherited. In an affected individual, it occurs as a random event during cell division in early fetal development. As a result, some of an affected person's cells have the usual two sex chromosomes, and other cells have only one copy of the X chromosome. Other sex chromosome abnormalities are also possible in females with X chromosome mosaicism.

Rarely, Turner syndrome caused by a partial deletion of the X chromosome can be passed from one generation to the next.

Symptoms

Possible findings of the head and neck include:

• Ears are low-set.
• Neck appears wide or web-like.
• Roof of the mouth is narrow (high palate).
• Hairline at the back of the head is lower.
• Lower jaw is lower and appears to fade away (recede).
• Drooping eyelids and dry eyes.

Other findings may include:

• Fingers and toes are short.
• Hands and feet are swollen in infants.
• Nails are narrow and turn upward.
• Chest is broad and flat. Nipples appear more widely spaced.
• Height at birth is often smaller than average.
• A child with Turner syndrome is much shorter than children who are the same age and sex. This is called short stature. This problem may not be noticed in girls before age 11.

Puberty may be absent or not complete. If puberty occurs, it most often begins at the normal age. After the age of puberty, unless treated with female hormones, these findings may be present:

• Pubic hair is often present and normal.
• Breast development may not occur.
• Menstrual periods are absent or very light.
• Vaginal dryness and pain with intercourse are common.
• Infertility.

Sometimes, the diagnosis of Turner syndrome may not be made until an adult. It may be discovered because a woman has very light or no menstrual periods and problems becoming pregnant.

Diagnosis

Turner syndrome can be diagnosed at any stage of life. It may be diagnosed before birth if:

• A chromosome analysis is done during prenatal testing.
• A cystic hygroma is a growth that often occurs in the head and neck area. This finding may be seen on ultrasound during the pregnancy and leads to further testing.
• The health care provider will perform a physical exam and look for signs of atypical development. Infants with

Turner syndrome often have swollen hands and feet.

The following tests may be performed:

• Blood hormone levels (luteinizing hormone, estrogen, and follicle-stimulating hormone)
• Echocardiogram
• Karyotyping
• MRI of the chest
• Ultrasound of reproductive organs and kidneys
• Pelvic exam

Other tests that may be done periodically include:

• Blood pressure screening
• Thyroid checks
• Blood tests for lipids and glucose
• Hearing screening
• Eye exam
• Bone density testing

Treatment

Growth hormone may help a child with Turner syndrome grow taller.

Estrogen and other hormones are often started when the girl is 12 or 13 years old. These help trigger the growth of breasts, pubic hair, other sexual characteristics, and growth in height. Estrogen therapy is continued through life until the age of menopause. Women with Turner syndrome who wish to become pregnant may consider using a donor egg.

Women with Turner syndrome may need care or monitoring for the following health problems:

• Keloid formation
• Hearing loss
• High blood pressure
• Diabetes
• Thinning of the bones (osteoporosis)
• Widening of the aorta and narrowing of the aortic valve
• Cataracts
• Obesity

Other issues may include:

• Weight management
• Exercise
• Transition to adulthood
• Stress and depression over changes

The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

• Somatropin (r-DNA) for injection (Brand name: Humatrope) For the treatment of short stature associated with Turner syndrome in patients whose epiphyses are not closed. In addition, for the treatment of short stature or growth failure in children with cuases of SHOX (short stature homeobox-containing gene) deficiency whose epiphyses are not closed.
• Somatropin (r-DNA) for injection (Brand name: Nutropin AQ) For the treatment of growth failure associated with Turner syndrome.
• Somatropin (r-DNA) for injection (Brand name: Nutropin AQ)For use in the long-term treatment of children who have growth failure due to a lack of adequate endogenous growth hormone secretion. Also for treatment of children with growth failure associated with chronic renal insufficiency and as replacement therapy for growth hormone deficiency in adults after epiphyseal closure.

Prognosis

The long-term outlook (prognosis) for people with Turner syndrome is typically good. Life expectancy is slightly shorter than average but may be improved by addressing and treating associated chronic illnesses, such as obesity and hypertension.[3] Regular checkups have shown substantial improvements in the quality and length of life for women with Turner syndrome. While almost all women are infertile, pregnancy with donor eggs and assisted reproductive technology is possible. Even with growth hormone therapy, most affected people are shorter than average.

NIH genetic and rare disease info

• NIH info on Turner syndrome

Turner syndrome is a rare disease.

Turner syndrome Resources
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