Turner syndrome

Turner syndrome (TS), also known 45,X, or 45,X0, is a genetic condition in which a female is partly or completely missing an X chromosome.[2] Signs and symptoms vary among those affected.[1] Often, a short and webbed neck, low-set ears, low hairline at the back of the neck, short stature, and swollen hands and feet are seen at birth.[1] Typically, they develop menstrual periods and breasts only with hormone treatment, and are unable to have children without reproductive technology.[1] Heart defects, diabetes, and low thyroid hormone occur more frequently.[1] Most people with TS have normal intelligence, however many have troubles with spatial visualization that may be needed for mathematics.[1] Vision and hearing problems occur more often.[5]

Turner syndrome
Other namesUllrich–Turner syndrome; Bonnevie–Ullrich–Turner syndrome; gonadal dysgenesis; 45X; 45X0
Girl with Turner syndrome before and after an operation for neck-webbing
SpecialtyPediatrics, medical genetics
SymptomsWebbed neck, short stature, swollen hands and feet[1]
ComplicationsHeart defects, diabetes, low thyroid hormone[1]
Usual onsetAt birth[1]
DurationLong term
CausesMissing X chromosome[2]
Diagnostic methodPhysical signs, genetic testing[3]
MedicationHuman growth hormone, estrogen replacement therapy[4]
PrognosisShorter life expectancy[5]
Frequency1 in 2,000 to 5,000[6][7]

Turner syndrome is not usually inherited; rather, it occurs during formation of the reproductive cells in a parent or in early cell division during development.[8][9] No environmental risks are known, and the mother's age does not play a role.[8][10] Turner syndrome is due to a chromosomal abnormality in which all or part of one of the X chromosomes is missing or altered.[11] While most people have 46 chromosomes, people with TS usually have 45.[11] The chromosomal abnormality may be present in just some cells in which case it is known as TS with mosaicism.[5] In these cases, the symptoms are usually fewer and possibly none occur at all.[12] Diagnosis is based on physical signs and genetic testing.[3]

No cure for Turner syndrome is known.[4] Treatment may help with symptoms.[4] Human growth hormone injections during childhood may increase adult height.[4] Estrogen replacement therapy can promote development of the breasts and hips.[4] Medical care is often required to manage other health problems with which TS is associated.[4]

Turner syndrome occurs in between one in 2,000[6] and one in 5,000 females at birth.[7] All regions of the world and cultures are affected about equally.[8] Generally people with TS have a shorter life expectancy, mostly due to heart problems and diabetes.[5] Henry Turner first described the condition in 1938.[13] In 1964, it was determined to be due to a chromosomal abnormality.[13]

Signs and symptoms
Lymphedema, puffy legs of a newborn with Turner syndrome

Of the following common symptoms of Turner syndrome, an individual may have any combination of symptoms and is unlikely to have all symptoms.

Other features may include a small lower jaw (micrognathia), cubitus valgus,[14] soft upturned nails, palmar crease, and drooping eyelids. Less common are pigmented moles, hearing loss, and a high-arch palate (narrow maxilla). Turner syndrome manifests itself differently in each female affected by the condition; therefore, no two individuals share the same features.

While most of the physical findings are harmless, significant medical problems can be associated with the syndrome. Most of these significant conditions are treatable with surgery and medication.[15]

Prenatal

Despite the excellent postnatal prognosis, 99% of Turner syndrome conceptions are thought to end in miscarriage or stillbirth,[16] and as many as 15% of all spontaneous abortions have the 45,X karyotype.[17][18] Among cases that are detected by routine amniocentesis or chorionic villus sampling, one study found that the prevalence of Turner syndrome among tested pregnancies was 5.58 and 13.3 times higher, respectively, than among live neonates in a similar population.[19]

Cardiovascular

The rate of cardiovascular malformations among patients with Turner syndrome ranges from 17%[20] to 45%.[21] The variations found in the different studies are mainly attributable to variations in noninvasive methods used for screening and the types of lesions that they can characterize.[22] However,[23] it could be simply attributable to the small number of subjects in most studies.

Different karyotypes may have differing rates of cardiovascular malformations. Two studies found a rate of cardiovascular malformations of 30%[24] and 38%[25] in a group of pure 45,X monosomy. Considering other karyotype groups, though, they reported a prevalence of 24.3%[24] and 11%[25] in people with mosaic X monosomy, and a rate of 11% in people with X chromosomal structural abnormalities.[24]

The higher rate in the group of pure 45,X monosomy is primarily due to a difference in the rate of aortic valve abnormalities and coarctation of the aorta, the two most common cardiovascular malformations.

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 includes bicuspid aortic valve and coarctation (narrowing) of the aorta. More than 50% of the cardiovascular malformations of individuals with Turner syndrome in one study were bicuspid aortic valves or coarctation of the aorta (usually preductal), alone or in combination.[23]

Other congenital cardiovascular malformations, such as partial anomalous venous drainage and aortic valve stenosis or aortic regurgitation, are also more common in Turner syndrome than in the general population. Hypoplastic left heart syndrome represents the most severe reduction in left-sided structures.

Bicuspid aortic valve

Up to 15% of adults with Turner syndrome have bicuspid aortic valves, meaning only two, instead of three, parts to the valves in the main blood vessel leading from the heart are present. Since bicuspid valves are capable of regulating blood flow properly, this condition may go undetected without regular screening. However, bicuspid valves are more likely to deteriorate and later fail. Calcification also occurs in the valves,[26] which may lead to a progressive valvular dysfunction as evidenced by aortic stenosis or regurgitation.[27]

With a rate from 12.5%[24] to 17.5% (Dawson-Falk et al., 1992), bicuspid aortic valve is the most common congenital malformation affecting the heart in this syndrome. It is usually isolated, but it may be seen in combination with other anomalies, particularly coarctation of the aorta.

Coarctation of the aorta

Between 5% and 10% of those born with Turner syndrome have coarctation of the aorta, a congenital narrowing of the descending aorta, usually just distal to the origin of the left subclavian artery (the artery that branches off the arch of the aorta to the left arm) and opposite to the ductus arteriosus (termed "juxtaductal"). Estimates of the prevalence of this malformation in patients with Turner syndrome range from 6.9[24] to 12.5%. A coarctation of the aorta in a female is suggestive of Turner syndrome and suggests the need for further tests, such as a karyotype.

Partial anomalous venous drainage

This abnormality is a relatively rare congenital heart disease in the general population. The prevalence of this abnormality also is low (around 2.9%) in Turner syndrome. However, its relative risk is 320 in comparison with the general population. Strangely, Turner syndrome seems to be associated with unusual forms of partial anomalous venous drainage.[24][28]

In a patient with Turner syndrome, these left-sided cardiovascular malformations can result in an increased susceptibility to bacterial endocarditis. Therefore, prophylactic antibiotics should be considered when procedures with a high risk of endocarditis are performed, such as dental cleaning.[27]

Turner syndrome is often associated with persistent hypertension, sometimes in childhood. In the majority of Turner syndrome patients with hypertension, no specific cause is known. In the remainder, it is usually associated with cardiovascular or kidney abnormalities, including coarctation of the aorta.

Aortic dilation, dissection, and rupture

Two studies have 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.[29]

  • A study that evaluated 28 girls with Turner syndrome found a greater mean aortic root diameter in people with Turner syndrome than in the control group (matched for body surface area). Nonetheless, the aortic root diameters found in Turner syndrome patients were still well within the limits.[30]
  • This has been confirmed by a study that evaluated 40 patients with Turner syndrome.[21] The study presented basically the same findings: a greater mean aortic root diameter, which nevertheless remains within the normal range for body surface area.

Whether aortic root diameters that are relatively large for body surface area but still well within normal limits imply a risk for progressive dilatation remains unproven.[23]

Rate of aortic abnormalities

The prevalence of aortic root dilatation ranges from 8.8[29] to 42%[27] in patients with Turner syndrome. Even if not every aortic root dilatation necessarily goes on to an aortic dissection (circumferential or transverse tear of the intima), complications such as dissection, aortic rupture resulting in death may occur. The natural history of aortic root dilatation is still unknown, but it is linked to aortic dissection and rupture, which has a high mortality rate.[31]

Aortic dissection affects 1 to 2% of patients with Turner syndrome. As a result, any aortic root dilatation should be seriously taken into account, as it could become a fatal aortic dissection. Routine surveillance is highly recommended.[27]

Risk factors for aortic rupture

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. Indeed, these same risk factors are found in more than 90% of patients with Turner syndrome who develop aortic dilatation. Only a small number of patients (around 10%) have no apparent predisposing risk factors. The risk of hypertension is increased three-fold in patients with Turner syndrome. Because of its relation to aortic dissection, blood pressure must be regularly monitored and hypertension should be treated aggressively with an aim to keep blood pressure below 140/80 mmHg. As with the other cardiovascular malformations, complications of aortic dilatation is commonly associated with 45,X karyotype.[27]

Pathogenesis of aortic dissection and rupture

The exact role that these risk factors play in the process leading to rupture is unclear. Aortic root dilatation is thought to be due to a mesenchymal defect as pathological evidence of cystic medial necrosis has been found by several studies. The association between a similar defect and aortic dilatation is well established in such conditions such as Marfan syndrome. Also, abnormalities in other mesenchymal tissues (bone matrix and lymphatic vessels) suggests a similar primary mesenchymal defect in patients with Turner syndrome.[29] However, no evidence suggests that patients with Turner syndrome have a significantly higher risk of aortic dilatation and dissection in absence of predisposing factors. So, the risk of aortic dissection in Turner syndrome appears to be a consequence of structural cardiovascular malformations and hemodynamic risk factors rather than a reflection of an inherent abnormality in connective tissue. The natural history of aortic root dilatation is unknown, but because of its lethal potential, this aortic abnormality needs to be carefully followed.

Skeletal

Normal skeletal development is inhibited due to a large variety of factors, mostly hormonal. The average height of a woman with Turner syndrome, in the absence of growth hormone treatment, is 4 ft 7 in (140 cm). Women with Turner's mosaicism can reach normal average height.

The fourth metacarpal bone (fourth toe and ring finger) may be unusually short, as may the fifth.

Due to inadequate production 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

About one-third of all women with Turner syndrome have one of three kidney abnormalities:

  1. A single, horseshoe-shaped kidney on one side of the body
  2. An abnormal urine-collecting system
  3. Poor blood flow to the kidneys

Some of these conditions can be corrected surgically. Even with these abnormalities, the kidneys of most women with Turner syndrome function normally. However, as noted above, kidney problems may be associated with hypertension.

Thyroid

Approximately one-third of all women with Turner syndrome have a thyroid disorder.[27] 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. The risk of developing type 2 diabetes can be substantially reduced by maintaining a healthy weight.

Cognitive

People with Turner syndrome have normal intelligence, and demonstrate relative strengths in verbal skills, but may exhibit weaker nonverbal skills – particularly in arithmetic, select visuospatial skills, and processing speed.[32] Turner syndrome does not typically cause intellectual disability or impair cognition. However, learning difficulties are common among women with Turner syndrome, particularly a specific difficulty in perceiving spatial relationships, such as nonverbal learning disorder. This may also manifest itself as a difficulty with motor control or with mathematics.[33] While it is not correctable, in most cases it does not cause difficulty in daily living. Most Turner syndrome patients are employed as adults and lead productive lives.

Also, a rare variety of Turner syndrome, known as "Ring-X Turner syndrome", has about a 60% association with intellectual disability. This variety accounts for around 2–4% of all Turner syndrome cases.[34]

Psychological

Social difficulties appear to be an area of vulnerability for young women.[35] Counseling affected individuals and their families about the need to carefully develop social skills and relationships may prove useful in advancing social adaptation. Women with Turner syndrome may experience adverse psychosocial outcomes which can be improved through early intervention and the provision of appropriate psychological and psychiatric care. Genetic, hormonal, and medical problems associated with TS are likely to affect psychosexual development of female adolescent patients, and thus influence their psychological functioning, behavior patterns, social interactions, and learning ability. Although TS constitutes a chronic medical condition, with possible physical, social, and psychological complications in a woman's life, hormonal and estrogen replacement therapy, and assisted reproduction, are treatments that can be helpful for TS patients and improve their quality of life.[36] Research shows a possible association between age at diagnosis and increased substance use and depressive symptoms.[37]

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 45,X.[38][39] Even when such pregnancies do occur, there is a higher than average risk of miscarriage or birth defects, including Turner syndrome or Down syndrome.[40] Some women with Turner syndrome who are unable to conceive without medical intervention may be able to use IVF or other fertility treatments.[41]

Usually, estrogen replacement therapy is used to spur the growth of secondary sexual characteristics at the time when puberty should onset. While very few women with Turner syndrome menstruate spontaneously, estrogen therapy requires a regular shedding of the uterine lining ("withdrawal bleeding") to prevent its overgrowth. Withdrawal bleeding can be induced monthly, like menstruation, or less often, usually every three months, if the patient desires. Estrogen therapy does not make a woman with nonfunctional ovaries fertile, but it plays an important role in assisted reproduction; the health of the uterus must be maintained with estrogen if an eligible woman with Turner Syndrome wishes to use IVF (using donated oocytes).

Especially in mosaic cases of Turner syndrome that contains Y-chromosome (e.g. 45,X/46,XY) due to the risk of development of ovarian malignancy (most common is gonadoblastoma) gonadectomy is recommended.[27][42] Turner syndrome is characterized by primary amenorrhoea, premature ovarian failure (hypergonadotropic hypogonadism), streak gonads and infertility (however, technology (especially oocyte donation) provides the opportunity of pregnancy in these patients). Failure to develop secondary sex characteristics (sexual infantilism) is typical.

As more women with Turner syndrome complete pregnancy thanks to modern techniques to treat infertility, it has to be noted that pregnancy may be a risk of cardiovascular complications for the mother. Indeed, several studies had suggested an increased risk for aortic dissection in pregnancy.[29] The influence of estrogen has been examined but remains unclear. It seems that the high risk of aortic dissection during pregnancy in women with Turner syndrome may be due to the increased hemodynamic load rather than the high estrogen level.[27]

Hearing

Recurrent acute otitis media (AOM) and otitis media with effusion (OME) commonly occur in children with Turner syndrome during the preschool age, which can persist or develop later in childhood. The recurring AOM can also be a predisposition to cholesteatomas.[43][44] People with the monosomy 45, X karyotype have an increased rate of hearing loss over other TS karyotype variants. Conductive hearing losses are more commonly seen with children than adults and becomes more of a sensorineural pattern once in the adolescence age. There seems to be an apparent linear relation between hearing loss and age in TS.[45][46] About 75% of people with Turner syndrome have some hearing loss, with the most common presenting as a high frequency sensorineural hearing loss (HFSNHL) across all ages.[47][48][49] People with TS tend to have more of a progressive hearing loss with a higher decline rate than those in their corresponding age groups with hearing loss. The increased decline tends to occur in the higher frequency range, with a rate of around 0.8-2.2 dB a year.[50]

Cause

Turner syndrome is caused by the absence of one complete or partial copy of the X chromosome in some or all the cells. The abnormal cells may have only one X (monosomy) (45,X) or they may be affected by one of several types of partial monosomy like a deletion of the short p arm of one X chromosome (46,X,del(Xp)) or the presence of an isochromosome with two q arms (46,X,i(Xq))[51] Turner syndrome has distinct features due to the lack of pseudoautosomal regions, which are typically spared from X-inactivation.[5] In mosaic individuals, cells with X monosomy (45,X) may occur along with cells that are normal (46,XX), cells that have partial monosomies, or cells that have a Y chromosome (46,XY).[51] The presence of mosaicism is estimated to be relatively common in affected individuals (67–90%).[51]

Inheritance

In the majority of cases where monosomy occurs, the X chromosome comes from the mother.[52] This may be due to a nondisjunction in the father. Meiotic errors that lead to the production of X with p arm deletions or abnormal Y chromosomes are also mostly found in the father.[53] Isochromosome X or ring chromosome X on the other hand are formed equally often by both parents.[53] Overall, the functional X chromosome usually comes from the mother.

In most cases, Turner syndrome is a sporadic event, and for the parents of an individual with Turner syndrome the risk of recurrence is not increased for subsequent pregnancies. Rare exceptions may include the presence of a balanced translocation of the X chromosome in a parent, or where the mother has 45,X mosaicism restricted to her germ cells.[54]

Diagnosis

Prenatal
45,X karyotype, showing an unpaired X at the lower right

Turner syndrome may be diagnosed by amniocentesis or chorionic villus sampling during pregnancy.

Usually, fetuses with Turner syndrome can be identified by abnormal ultrasound findings (i.e., heart defect, kidney abnormality, cystic hygroma, ascites). In a study of 19 European registries, 67.2% of prenatally diagnosed cases of Turner syndrome were detected by abnormalities on ultrasound. 69.1% of cases had one anomaly present, and 30.9% had two or more anomalies.[55]

An increased risk of Turner syndrome may also be indicated by abnormal triple or quadruple maternal serum screen. The fetuses diagnosed through positive maternal serum screening are more often found to have a mosaic karyotype than those diagnosed based on ultrasonographic abnormalities, and conversely, those with mosaic karyotypes are less likely to have associated ultrasound abnormalities.[55]

Postnatal

Turner syndrome can be diagnosed postnatally at any age. Often, it is diagnosed at birth due to heart problems, an unusually wide neck or swelling of the hands and feet. However, it is also common for it to go undiagnosed for several years, often until the girl reaches the age of puberty and fails to develop typically (the changes associated with puberty do not occur). In childhood, a short stature can be indicative of Turner syndrome.[56]

A test called a karyotype, also known as a chromosome analysis, analyzes the chromosomal composition of the individual. This is the test of choice to diagnose Turner syndrome.

Treatment

As a chromosomal condition, there is no cure for Turner syndrome. However, much can be done to minimize the symptoms. For example:[57]

  • Growth hormone, either alone or with a low dose of androgen, will increase growth and probably final adult height. Growth hormone is approved by the U.S. Food and Drug Administration for treatment of Turner syndrome and is covered by many insurance plans.[57][58] There is evidence that this is effective, even in toddlers.[59]
  • Estrogen replacement therapy such as the birth control pill, has been used since the condition was described in 1938 to promote development of secondary sexual characteristics. Estrogens are crucial for maintaining good bone integrity, cardiovascular health and tissue health.[57] Women with Turner syndrome who do not have spontaneous puberty and who are not treated with estrogen are at high risk for osteoporosis and heart conditions.
  • Modern reproductive technologies have also been used to help women with Turner syndrome become pregnant if they desire. For example, a donor egg can be used to create an embryo, which is carried by the Turner syndrome woman.[57]
  • Uterine maturity is positively associated with years of estrogen use, history of spontaneous menarche, and negatively associated with the lack of current hormone replacement therapy.[60]

Epidemiology

Turner syndrome occurs in between one in 2000[6] and one in 5000 females at birth.[7]

Approximately 99 percent of fetuses with Turner syndrome spontaneously terminate during the first trimester.[61] Turner syndrome accounts for about 10 percent of the total number of spontaneous abortions in the United States.[27]

History

The syndrome is named after Henry Turner, an endocrinologist from Illinois, who described it in 1938.[62] In Europe, it is often called Ullrich–Turner syndrome or even Bonnevie–Ullrich–Turner syndrome to acknowledge that earlier cases had also been described by European doctors. In Russian and USSR literature it is called Shereshevsky–Turner syndrome to acknowledge that the condition was first described as hereditary in 1925 by the Soviet endocrinologist Nikolai Shereshevsky, who believed that it was due to the underdevelopment of the gonads and the anterior pituitary gland and was combined with congenital malformations of internal development.[63]

The first published report of a female with a 45,X karyotype was in 1959 by Dr. Charles Ford and colleagues in Harwell near Oxford, and Guy's Hospital in London.[64] It was found in a 14-year-old girl with signs of Turner syndrome.

See also

References
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