Turner Syndrome

What is Turner syndrome?

Turner syndrome is caused by a missing or incomplete X chromosome. People who have Turner syndrome develop as females. SOme of the genes on the X chromosome are involved in growth and sexual development, which is why girls with the disorder are shorter than normal and have incompletely developed sexual characteristics.

To learn more about nondisjunction, visit Using Karyotypes to Diagnose Genetic Disorders
Turner Karyotype

How do people get Turner syndrome?

Normally, a girl inherits one X chromosome from her mother and one X chromosome from her father. But girls who have Turner syndrome are missing one of their X chromosomes.

Turner syndrome is typically caused by what is called nondisjunction. Nondisjunction happens when a pair of sex chromosomes fails to separate during the formation of a sperm (or egg). When sperm with no X chromosome unites with a normal egg to form an embryo, that embryo will have just one X chromosome (X rather than XX). As the embryo grows and the cells divide, the X chromosome will be missing from every cell of the baby's body.

The abnormality is not inherited from an affected parent (not passed down from parent to child), because women with Turner syndrome are usually sterile and cannot have children.

In about 20 percent of Turner syndrome cases, both X chromosomes are present, but one is abnormal. It may be shaped like a ring or missing some genetic material.

About 30 percent of girls with the disorder are missing the X chromosome in just some of their cells. This mixed chromosome pattern is known as mosaicism. Girls with this pattern may have fewer symptoms because they still have some normal (XX) cells.

One of the missing genes on the X chromosome is the SHOX gene, which is responsible for long bone growth. The missing SHOX gene is the reason girls who have the disorder are unusually short. Other missing genes regulate ovarian development, which influences sexual characteristics.

Nondisjunction

Nondisjunction happens when chromosomes are distributed incorrectly during egg and sperm formation. The gametes above either are missing or have an extra X chromosome.


What are the symptoms of Turner syndrome?

Turner syndrome affects growth and sexual development. Girls with this disorder are shorter than normal and may not start puberty when they should. This is because the ovaries (which produce eggs, as well as the sex hormones estrogen and progesterone) don't develop properly.

Turner syndrome usually does not affect intelligence. Common physical symptoms of Turner Syndrome include a stocky build, arms that turn out slightly at the elbow, a receding lower jaw, a short webbed neck, and a low hairline at the back of the neck.

Medical symptoms can include lymphedema (swelling of hands and feet), heart and/or kidney defects, high blood pressure, and infertility (inability to have children).

Turner Syndrome

How do doctors diagnose Turner syndrome?

About half of the cases are diagnosed within the first few months of a girl's life by the characteristic symptoms (swelling of the hands and feet, heart defect). Other patients are diagnosed in adolescence because they do not grow normally or go through puberty.

When a doctor suspects Turner syndrome, a blood sample can be used to make a karyotype (a chromosome analysis), and the diagnosis can be confirmed.

Turner syndrome may be diagnosed during pregnancy with chorionic villus sampling (CVS) or amniocentesis. Alternatively, an ultrasound (a machine that uses sound waves to look inside a mother's uterus) can identify the disorder by its physical symptoms before the baby is born.


How is Turner syndrome treated?

Hormone replacement therapy is the best way to treat this disorder. Teenagers are treated with growth hormone to help them reach a normal height. They may also be given low doses of androgens (male hormones that females also produce in small quantities) to increase height and encourage hair and muscle growth. Some patients may take the female hormone estrogen to promote sexual development.


Interesting facts about Turner syndrome

Turner Syndrome affects 60,000 females in the United States. This disorder is seen in 1 of every 2000 to 2500 baby girls, with about 800 new cases diagnosed each year.

In 75-80% of cases, the single X chromosome comes from the mother's egg; the father's sperm that fertilizes the egg is missing its sex chromosome.

Turner syndrome is named for Dr. Henry Turner, who in 1938 published a report describing the disorder.

The average height of an untreated woman with Turner syndrome is 4 feet 8 inches.

A female fetus (normally XX) that is missing one of its X chromosomes can survive, but a male fetus (normally XY) cannot. The X chromosome is a long DNA molecule with many genes that are needed for cells to function; it is essential for life. In contrast, the Y chromosome carries few genes and is not essential for life.

+1.801.585.3470

383 Colorow Dr, Salt Lake City, Utah 84108

APA format:
Genetic Science Learning Center (2014, June 22) Turner Syndrome. Learn.Genetics. Retrieved July 31, 2014, from http://learn.genetics.utah.edu/content/disorders/chromosomal/turner/
MLA format:
Genetic Science Learning Center. "Turner Syndrome." Learn.Genetics 31 July 2014 <http://learn.genetics.utah.edu/content/disorders/chromosomal/turner/>
Chicago format:
Genetic Science Learning Center, "Turner Syndrome," Learn.Genetics, 22 June 2014, <http://learn.genetics.utah.edu/content/disorders/chromosomal/turner/> (31 July 2014)