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Turner's syndrome

Turner syndrome is a human genetic abnormality, caused by a nondisjunction in the sex chromosomes that occurs in females (1 out of every 2,500 births). Instead of the normal XX sex chromosomes, only one X chromosome is present and fully functional; this is called 45,X or X0. In Turner syndrome, female sexual characteristics are present but underdeveloped. more...

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Symptoms

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
  • Reproductive sterility

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 different people, and no two women need share the same symptoms.

Causes

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.

Incidence

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.

History

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.

Diagnosis

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.

A blood test, called a karyotype, analyzes the chromosomal composition of the individual. This is the most commonly used blood test to diagnose Turner syndrome.

Medical consequences of Turner syndrome

While most of the symptoms of Turner syndrome are harmless, some can lead to significant medical problems.

Cardiovascular

It is interesting for a better understanding to first consider the results of Price et al, 1986 study of 156 female patients with Turner syndrome. Indeed they showed a significantly greater number of deaths from diseases of the circulatory system than expected, half of them due to congenital heart disease. The interesting finding is that when patients with congenital heart disease were omitted from the sample of the study, the mortality from circulatory disorders was not significantly increased.

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Aortic dissection: turner's patients at risk for cardiac complications
From OB/GYN News, 7/15/04 by Betsy Bates

LA JOLLA, CALIF. -- Four pregnancy-related deaths due to aortic dissection and a fifth report describing a woman who survived a dissection 2 weeks after a cesarean section have raised questions about whether Turner's syndrome patients are good candidates for childbearing, even though in vitro fertilization has led many to pursue pregnancy using donor oocytes.

The maternal mortality rate, based on 194 known in vitro fertilization (IVF) pregnancies in Turner's syndrome patients, is estimated to be 2%, Dr. Richard H. Reindollar reported during the annual meeting of the North American Society for Pediatric and Adolescent Gynecology.

However, the maternal mortality rate could be even higher than 2%. "This is something we should think long and hard about" as more of these patients pursue pregnancy, said Dr. Reindollar, who is the director of reproductive endocrinology and infertility at Beth Israel Deaconess Medical Center in Boston.

Just because donor oocyte IVF can be used to help these patients become pregnant doesn't mean that it should be used. He stressed that increased cardiac demands of pregnancy may be especially perilous for Turner's syndrome patients, who may be at risk for aortic dilation, dissection, and rupture, even in the absence of risk factors.

He and his associates conducted a survey of 259 donor oocyte programs and found that fewer than half of Turner syndrome patients were screened with echocardiography as part of their work-up (Fertil. Steril. 80[3]:498-501, 2003). Among the 72 screened patients, 6 (8%) had abnormal results.

A subsequent literature review by Dr. Reindollar's team at the medical center and Harvard Medical School in Boston turned up four deaths. They included:

* Two deaths reported in 1997, both of which involved aortic dissection in the third trimester. One patient had a history of hypertension and a slightly dilated aorta.

* One death after surgical intervention in a woman whose aortic dissection was diagnosed late in a pregnancy complicated by preeclampsia.

* One death associated with aortic dissection at 36 weeks' gestation in a patient with a history of juxtaductal coarctation repaired during childhood.

In addition, Dr. Reindollar identified a case in which a Turner's syndrome patient who did not have any risk factors suffered an aortic dissection 2 weeks after a cesarean section for eclampsia. That patient survived.

Dr. Reindollar said spontaneous pregnancy is very rare in Turner's syndrome patients, who are born with complete or partial absence of the second sex chromosome.

Only about 5% of patients have menstrual periods, and roughly 1% becomes pregnant naturally. These pregnancies are associated with a very high loss rate as well as a high rate of congenital anomalies.

A 1998 review of 160 spontaneous pregnancies found that only 38% resulted in the birth of healthy children with normal karyotypes (Gynecol. Endocrinol. 12[2]:83-87, 1998).

The advent of IVF, however, provided new reproductive possibilities to Turner's syndrome patients, since the vast majority have normal uteri and are physically capable of becoming pregnant by using donor oocytes. The first such pregnancy was reported in 1988, and the largest series reported to date found a 19% "take-home baby" rate per cycle (Hum. Reprod. 12[2]:279-85, 1997).

Results of Dr. Reindollar's survey demonstrated, however, that many fertility specialists had "no clue" about the cardiac risks facing Turner's syndrome patients. That may be because most of the 14 major articles on the subject have appeared in journals read by geneticists, cardiologists, and pediatricians but rarely studied by obstetricians, gynecologists, or endocrinologists, he said.

These studies detail numerous cases of aortic aneurysm, dissection, or rupture in nonpregnant patients and note that some share histopathologic features, such as cystic medial necrosis, with Marfan syndrome patients (Pediatrics 102[1]:e12, 1998). Pregnancy is contraindicated in Marfan syndrome patients with aortic dilation, he noted.

Dr. Reindollar said nonpregnant Turner's syndrome patients should undergo annual cardiac, blood pressure, and x-ray examinations and should have echocardiography screening every 3-5 years. If the descending aorta cannot be inspected, patients should have an MRI. He also recommended that patients wear a medical identification bracelet noting their risk of dissection even in the absence of risk factors.

Patients considering pregnancy should be extensively counseled about the risks, benefits, contraindications, and warning symptoms of catastrophic cardiac complications. In those patients who decide to pursue pregnancy despite the risks, Dr. Reindollar suggested a baseline cardiac evaluation, including a consultation with a cardiologist, and an echocardiography each trimester.

BY BETSY BATES

Los Angeles Bureau

COPYRIGHT 2004 International Medical News Group
COPYRIGHT 2004 Gale Group

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