Turner syndrome

Turner syndrome (TS), also known as 45,X, or 45,X0, is a genetic condition in which a female is partially or completely missing an X chromosome. Signs and symptoms vary among those affected. 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. Typically, those affected do not develop menstrual periods, or breasts without hormone treatment and are unable to have children without reproductive technology. Heart defects, diabetes, and low thyroid hormone occur in the disorder more frequently than average. Most people with Turner syndrome have normal intelligence; however, many have problems with spatial visualization that may be needed in order to learn mathematics. Vision and hearing problems also occur more often than average.

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. No environmental risks are known, and the mother's age. In these cases the symptoms are usually fewer, and possibly none occur at all. Diagnosis is based on physical signs and genetic testing.

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

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

Presentation

Turner syndrome has a number of physical and psychological impacts, including short stature, heart defects, neck webbing, delayed or absent puberty, and infertility. The phenotype of Turner syndrome is affected by mosaicism, where cell lines with a single sex chromosome are combined with those with multiple. Around 40%–50% of cases of Turner syndrome are true "monosomy X" with a 45,X0 karyotype, while the remainder are mosaic for another cell line, most commonly 46,XX, or have other structural abnormalities of the X chromosome. The classic features of Turner syndrome, while distinctive, may be rarer than previously thought; incidental diagnosis, such as in biobank samples or prenatal testing for older mothers, finds many girls and women with few traditional signs of Turner syndrome.

Physiological

Height

Turner syndrome is associated with short stature. The mean adult height of women with Turner syndrome without growth hormone therapy is around shorter than the mean of women in the general population. Mosaicism affects height in Turner syndrome; a large population sample drawn from the UK Biobank found women with 45,X0 karyotypes to have an average height of , while those with 45,X0/46,XX karyotypes averaged . The strength of the association between Turner syndrome and short stature is such that idiopathic short stature alone is a major diagnostic indication.

Growth delay in Turner syndrome does not begin at birth; most neonates with the condition have a birth weight in the lower end of the normal range. Height begins to lag in toddlerhood, with a delayed growth velocity becoming apparent as early as 18 months. When girls with Turner syndrome begin school, their height is usually still not remarkably unusual; marked short stature becomes obvious in mid-childhood. In undiagnosed preadolescents and adolescents, growth delay may be mistaken for a side effect of delayed puberty and improperly treated. Short stature in Turner syndrome and its counterpoint, tall stature in sex chromosome polysomy conditions such as Klinefelter syndrome, XYY syndrome, and trisomy X, is caused by the short-stature homeobox gene on the X and Y chromosomes. The absence of a copy of the ''SHOX'' gene in Turner's inhibits skeletal growth, resulting both in overall short stature and in a distinctive pattern of skeletal malformations including micrognathia (small chin), cubitus valgus (abnormal forearm angles), and short fingers.

When Turner syndrome is diagnosed in early life, growth hormone therapy can decrease the degree of short stature. The use of growth hormone therapy in Turner's originated from a series of studies in the 1980s finding it to substantially increase the height of treated girls, compared to prior adult height predictions and Turner's growth charts; treatment with human growth hormone appears to increase expected adult height by approximately from an otherwise expected norm of –. In some cases oxandrolone, a steroid with a relatively mild masculinizing effect, may be used alongside growth hormone. The addition of oxandrolone to a Turner's treatment regimen adds around to the final height. Oxandrolone is used particularly often in girls diagnosed later in their growth period, due to the reduced impact of growth hormone alone in this population. However, oxandrolone use runs the risk of delayed breast development, voice deepening, increased body hair, or clitoromegaly. The effects of growth hormone therapy are at their strongest during the first year of treatment and taper off over time.

Physical features

In addition to short stature, Turner syndrome is associated with a number of characteristic physical features. These include a webbed neck, a low hairline, a small chin and jaw, a high-arched palate, and a broad chest with wide-spaced nipples. Lymphedema (swelling) of the hands and feet is common at birth and sometimes persistent throughout the lifespan. Some Turner's stigmata, such as cubitus valgus and shortened fingers, are related to ''SHOX'' gene dosage effects.

A number of the external manifestations of Turner syndrome are focused on the limbs, hands, and feet. Lymphedema at birth is one of the classic features of the syndrome; though it often resolves during toddlerhood, recurrence in later life is frequent, often without apparent cause. Cases where the retained X chromosome was inherited from the mother more often experience lymphedema than those where it was from the father. As a consequence of lymphedema's effects on nail anatomy, females with Turner syndrome frequently have small hypoplastic

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