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Turner syndrome encompasses several chromosomal abnormalities, of which monosomy X, is the most common. It occurs in 1 out of every 2,500 female births•. Instead of the normal XX sex chromosomes for a female, only one X chromosome is present and fully functional. This is called 45,X or 45,X0, although other genetic variants occur. In Turner syndrome, female sexual characteristics are present but underdeveloped.
Symptoms Common symptoms of Turner syndrome include: Other symptoms include a small lower jaw, cubitus valgus (turned-in elbows), a webbed neck, soft upturned nails, Simian crease and drooping eyelids. Less common are pigmented moles, hearing loss, and a high-arch palate. Turner syndrome manifests itself differently in each female affected by the condition, and no two individuals will share the same symptoms. Genetics Turner syndrome is characterized by the presence of a single complete functioning sex-determining chromosome, the X chromosome, instead of two, either XX or XY. This chromosomal arrangement normally occurs in four ways. There is no equivalent syndrome which results in a Y chromosome with no X, as such a condition is incompatible with life. Because an embryo with Turner syndrome doesn't have a Y chromosome (or, doesn't have a functional SRY on the Y chromosome), it will move along the path to female development. Risk factors for Turner syndrome are not well known. Nondisjunctions increase with maternal age, such as for Down syndrome, but that effect is not clear 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 believed to be 1 in 2500. 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. The first published report of a female with a 45,X karyotype was in 1959 by Dr. Charles Ford and colleagues in Harwell, Oxfordshire and Guy's Hospital in London. It was found in a 14-year-old girl with signs of Turner syndrome. Diagnosis Turner syndrome may be diagnosed by 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. Prognosis While most of the symptoms of Turner syndrome are harmless, some can lead to significant medical problems. Cardiovascular Price et al (1986 study of 156 female patients with Turner syndrome) showed a significantly greater number of deaths from diseases of the circulatory system than expected, half of them due to congenital heart disease. When patients with congenital heart disease were omitted from the sample of the study, the mortality from circulatory disorders was not significantly increased. Cardiovascular malformations are a serious concern as it is the most common cause of death in adults with Turner syndrome. It takes an important part in the 3-fold increase in overall mortality and the reduced life expectancy (up to 13 years) associated with Turner syndrome. Often associated with webbing of the neck and coarctation of the aorta. Prevalence of cardiovascular malformations The prevalence of cardiovascular malformations among patients with Turner syndrome ranges from 17% (Landin-Wilhelmsen et al, 2001) to 45% (Dawson-Falk et al, 1992). The variations found in the different studies are mainly attributable to variations in non-invasive methods used for screening and the types of lesions that they can characterize (Ho et al, 2004). However Sybert, 1998 suggests that it could be simply attributable to the small number of subjects in most studies. Different karyotypes may have differing prevalence of cardiovascular malformations. Two studies found a prevalence of cardiovascular malformations of 30% (Mazanti et al, 1998 …594 patients with Turner syndrome) and 38% (Gotzsche et al, 1994 …393 patients with Turner syndrome) in a group of pure 45X monosomy. But considering other karyotype groups, they reported a prevalence of 24.3% (Mazanti et al, 1998) and 11% (Gotzsche et al, 1994) in patients with mosaic X monosomy , and Mazanti et al, 1998 found a prevalence of 11% in patients with X chromosomal structural abnormalities. The higher prevalence in the group of pure 45X monosomy is primarily due to a significant difference in the prevalence of aortic valve abnormalities and aortic coarctation, the two most common cardiovascular malformations. Though according to Sybert, 1998 there is inadequate data to allow conclusions for regarding phenotype-karyotype correlations in regard to cardiovascular malformations in Turner syndrome because the number of individuals with the less common karyotype groups that has been studied is too small. Other studies also suggest the presence of hidden mosaicisms that are not diagnosed on usual karyotypic analyses in some patients with 45X karyotype. In conclusion the associations between karyotype and phenotypic characteristics, including cardiovascular malformations, remain questionable. Congenital heart disease The most commonly observed are congenital obstructive lesions of the left side of the heart, leading to reduced flow on this side of the heart. This mainly includes bicuspid aortic valve and coarctation of the aorta. Sybert, 1998 found that more than 50% of the cardiovascular malformations observed in her study were bicuspid aortic valve or coarctation of the aorta alone or in combination. Other congenital cardiovascular malformations such partial anomalous venous drainage and aortic stenosis or regurgitation are also more common in Turner syndrome compared with the general population. Hypoplastic left heart syndrome represents the most severe reduction in left-sided structures. Though rare in the population at large, this feature is quite common in those with Turner syndrome. Bicuspid aortic valve. Up to 15% of adults with Turner syndrome have bicuspid aortic valves, meaning that there are only two, instead of three, parts to the valves in the main blood vessel leading from the heart. Since bicuspid valves are capable of regulating blood flow properly, this condition may go undetected without regular screening. However, bicuspid valves must work harder than ordinary heart valves and are therefore more likely to deteriorate and later fail. With a prevalence from 12.5% (Mazanti et al, 1998) to 17.5% (Dawson-Falk et al, 1992), Bicuspid aortic valve is the most common congenital malformation affecting the heart. Hypotheses have been proposed to explain this abnormal aortic valve but the pathogenesis remains unknown. It is usually isolated but it may be seen in combination with other anomalies, particularly coarctation of the aorta (a quite common association). As this malformation calcifies it may lead to a progressive valvular dysfunction as evidenced by aortic stenosis or regurgitation (Elsheikh et al, 2002). Coarctation of the aorta. Between 5% and 10% of those born with Turner syndrome have coarctation of the aorta, a condition which if untreated causes blood to flow in a thin, fast stream against the side of the heart. This can lead to heart rupture (see below). Coarctation of the aorta can be corrected surgically as soon as it is detected. Coarctation of the aorta consists in a congenital narrowing of the descending aorta, usually just distal to the origin of the left subclavian artery and opposite to the duct (and so termed “juxtaductal”). While it's more common in boys, estimates of the prevalence of this malformation in patients with Turner syndrome ranges from 6.9% (Mazanti et al, 1998) to 12.5% (Dawson-Falk et al, 1992). A coarctation of the aorta in a female might be quite suggestive of Turner syndrome. It has to be noted the important relative risk of 160 found by the Mazanti et al, 1998 study. Partial anomalous venous drainage. This abnormality is a relatively rare congenital heart disease in the general population. The prevalence of this abnormality is low (around 2.9%) in Turner syndrome. However, it is interesting to note that with a relative risk of 320 it is the highest risk, in comparison with the general population. Strangely, Turner syndrome seems to be associated with quite unusual forms of partial anomalous venous drainage. (Mazanti et al, 1998 and Prandstraller et al, 1999) For the management of a patient with Turner syndrome it is essential to keep in mind that all these left-sided cardiovascular malformations often found in Turner syndrome result in an increased susceptibility to infective endocarditis. Therefore prophylactic antibiotics should be considered when procedures with high risk of infection need to be performed (Elsheikh et al, 2002). Turner syndrome is often associated with persistent hypertension, sometimes even in childhood. In the majority of Turner syndrome patients with hypertension, there is no specific cause. In the remainder, it is usually associated with heart or kidney abnormalities. Aortic dilation, dissection and rupture Two studies had suggested aortic dilatation in Turner syndrome, typically involving the root of the ascending aorta and occasionally extending through the aortic arch to the descending aorta, or at the site of previous coarctation of the aorta repair (Lin et al, 1998). Prevalence The prevalence of aortic root dilatation ranges from 8,8% (Lin et al, 1986) to 42% (Elsheikh et al, 2001) in patients with Turner syndrome. Risk factors It is well established that cardiovascular malformations (typically bicuspid aortic valve, coarctation of the aorta and some other left-sided cardiac malformations) and hypertension predispose to aortic dilatation and dissection in the general population. Pathogenesis The exact role that all these risk factors play in the process leading to such fatal complications is still quite unclear. Pregnancy As more women with Turner syndrome complete pregnancy thanks to the new modern techniques to treat infertility, it has to be noted that pregnancy may be at risk for cardiovascular complications. Cardiovascular malformations in Turner syndrome are also very serious, not only because of their high prevalence in that particular population but mainly because of their high lethal potential and their great implication in the increased mortality found in patients with Turner syndrome. Congenital heart disease needs to be explored in every female newly diagnosed with Turner syndrome. As adults are concerned closed surveillance of blood pressure is highly needed to avoid a higher risk of fatal complications in aortic root dilatation. A greater knowledge of the natural history and pathogenesis is needed in order to propose a better management and prevention of these malformations. It would therefore be interesting to examine the different causes mentioned by some studies in order to explain why patients with Turner syndrome are more susceptible to cardiovascular malformations that the general population. Skeletal Normal skeletal development is inhibited due to a large variety of factors, mostly hormonal. The head, neck, and chest of women with Turner syndrome are usually of normal size, but the arms and legs are unusually short. The average height of a woman with Turner syndrome is 4'7", or about 140cm. The fourth metacarpal bone (fourth toe and ring finger) may be unusually short. Due to inadequate circulation of estrogen, many of those with Turner syndrome develop osteoporosis. This can decrease height further, as well as exacerbate the curvature of the spine, possibly leading to scoliosis. It is also associated with an increased risk of bone fractures. Kidney Approximately one-third of all women with Turner syndrome have one of three kidney abnormalities: Thyroid Approximately one-third of all women with Turner syndrome have a thyroid disorder. Usually it is hypothyroidism, specifically Hashimoto's thyroiditis. If detected, it can be easily treated with thyroid hormone supplements. Diabetes Women with Turner syndrome are at a moderately increased risk of developing type 1 diabetes in childhood and a substantially increased risk of developing type 2 diabetes by adult years. Cognitive Turner syndrome does not typically cause mental retardation or impair cognition. However, learning disabilities are common among women with Turner syndrome, particularly a specific difficulty in perceiving spatial relationships. This may also manifest itself as a difficulty with motor control or with mathematics. While it is non-correctable, in most cases it does not cause difficulty in daily living. Reproductive Women with Turner syndrome are almost universally infertile. While some women with Turner syndrome have successfully become pregnant and carried their pregnancies to term, this is very rare and is generally limited to those women whose karyotypes are not 45X0. Even when such pregnancies do occur, there is a higher than average risk of miscarriage or birth defects. Some women with Turner syndrome who are unable to conceive without medical intervention may be able to benefit from the use of IVF or other fertility treatments. Usually hormone replacement is used to spur growth of secondary sexual characteristics at the time when puberty should onset. This generally induces menstruation, though the vast majority of women with Turner syndrome will still be infertile. Treatment As a chromosomal condition, there is no "cure" for Turner syndrome. However much can be done to minimize the symptoms. For example: Sources See also | |||||||||||||||||||||||
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