Turner Syndrome

What is Turner syndrome?
Is it possible to test for Turner syndrome during pregnancy?
Where can I get more information about Turner syndrome?

What is Turner syndrome?
Turner syndrome is a sex chromosome abnormality affecting about 1 in every 2000 to 2500 newborns.¹ A syndrome is a pattern or combination of physical, mental and health characteristics that are usually seen together.¹ Turner syndrome is caused by the absence of all (or part of) one of the usual two X chromosomes found in the cells of a woman's body.² Typically, individuals have 46 chromosomes (23 pairs) in each cell with two copies of chromosome number 1, two copies of chromosome number 2, and so on up to chromosome number 23. The 23rd pair determines sex so that males generally have one X and one Y chromosome and females usually have two X chromosomes.¹

About 50% of women with Turner syndrome are missing one entire X chromosome (called monosomy X) in most or all of their cells.¹ Therefore, there are only 45 chromosomes total, instead of the usual 46. Other women with Turner syndrome may be missing only part of the X, or only some cells in the body are missing an X (called mosaicism).¹ When an X chromosome is missing, either in part or whole, overall physical development can be affected.

Features of Turner syndrome are highly variable in children and adults, but may include:^1,2

• Small jaw
• Short neck with extra skin folds and low hairline in back
• Broad chest
• Lymphedema (puffy hands and feet) at birth
• Kidney abnormalities
• Heart defects
• Short stature- average adult height is 4'8"
• Lack of menstruation in 99% of women
• Underdeveloped ovaries/ovarian failure
• Infertility
• Incomplete sexual development, lack of breast development in 90-95% of women
• Soft fingernails that turn up at the end
• Short 4th and 5th fingers
• Arms turn out slightly at elbows
• Pigmented nevi on skin (small brown moles on the skin)
• Prominent ears
• Usually normal IQ, not associated with mental retardation

Turner syndrome can be identified in a fetus during pregnancy. A developing baby with Turner syndrome may have lymphatic problems, such as cystic hygroma (collection of lymphatic fluid in the neck).³ Many pregnancies with Turner syndrome will not survive to delivery.⁴

Turner syndrome usually occurs by chance and is not associated with increasing maternal age.² Couples who have had one pregnancy with Turner syndrome are usually not at an increased risk above the risk associated with the mother's age to have another pregnancy with a chromosome abnormality. If Turner syndrome is caused by a X chromosome with a missing piece, this could be inherited and the couple and other relatives may have an increased chance of having a pregnancy with an X chromosome problem. ⁵

Is it possible to test for Turner syndrome during pregnancy?
It is possible to diagnose Turner syndrome during pregnancy through prenatal diagnostic procedures such as amniocentesis or CVS. Because amniocentesis and CVS pose some degree of risk to the pregnancy, they are generally reserved for those situations when the chance for diagnosing a chromosome problem is at least as high as the complication rate. For more complete discussions of these procedures, use these links:

Amniocentesis | CVS

Parents might consider amniocentesis or CVS when a mother's age is 35 years or older at delivery or there is a family history of a chromosome abnormality. Maternal serum screening, which has many other names, such as AFP and triple screen, does not provide any information about the risk for Turner syndrome. Ultrasound is a common screening test during pregnancy. There are some signs that may be seen on a thorough ultrasound (sometimes called level II or targeted) that may indicate there is an increased chance for Turner syndrome. For example, a cystic hygroma is a fluid filled sac at the back of the neck. ³ Cystic hygromas are often present when a developing baby has Turner syndrome. ³ If a cystic hygroma or other concerning ultrasound findings are present, the findings should be discussed in detail with a genetic counselor, doctor, or qualified health care provider.

The choice to have any type of screening or prenatal diagnosis procedure is very personal. It is important to fully understand the benefits and limitations of each of the options before making a decision. Genetic counselors are specially trained to guide couples through these options to a decision that seems most appropriate for them. If you would like more information about the availability of genetic counselors in your area, visit the National Society of Genetic Counselors Web Site.

Where can I get more information about Turner syndrome?

Turner Syndrome Society of the United States
www.turner-syndrome-us.org

References

1. Rieser PA, Underwood LE. Turner Syndrome: A Guide for Families. Turner Syndrome Society. Wayzata, Mn; 1992.
2. Turner Syndrome Society of the United States. Resources and Research: Frequently Asked Questions. Houston, Tx: Turner Syndrome Society of the US; [cited January 25, 2002]. www.turner-syndrome-us.org.
3. Sanders RC, ed. Structural Fetal Abnormalities: The Total Picture. St. Louis, Mo: Mosby; 1996:158.
4. Therman E, Susman M. Human Chromosomes: Structure, Behavior and Effects. 3rd ed. New York, NY, Springer-Verlag; 1993.
5. Harper, PS. Practical Genetic Counseling. 5th ed. Oxford, England: Butterworth-Heinemann; 1998.
   

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