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Turner's syndrome is a chromosomal abnormality characterized by an absence of all or part of one X chromosome. It has been described in many species, including humans, mice and horses.

Individuals with this disorder have a female phenotype or female physical appearance, abnormalities in reproductive function, as well as a number of other clinical manifestations of the disease.

Incidence

Turner's syndrome is the most common sex chromosome abnormality of human females. The incidence of this disorder in newborns is approximately 1 in 2,500. However, roughly 10% of spontaneously aborted fetuses have this disorder, and the incidence has been estimated as 0.8% in zygotes, making it possibly the most common chromosomal disorder affecting humans. Almost half of the females with Turner's syndrome have X chromosome monosomy (45, X). In roughly 2/3 of cases having a 45, X karyotype, the single X chromosome is of maternal origin. At least two X-linked genes known to not undergo inactivation in man do undergo inactivation in mice.

Possible causes 

Humans have 46 paired chromosomes, with two sex chromosomes that decide gender. The other 44 chromosomes dictate other factors. A female has two X chromosomes. However, in females with Turner’s syndrome, one of these chromosomes is absent or abnormal. The missing genes cause the range of anomalies and symptoms associated with this condition.  

Female phenotype

As said before, this characteristic condition is caused by the absence of a Y chromosome.

It has been proven that patients with Turner’s syndrome may have:
  • a short neck with a webbed appearance
  • a low hairline at the back of the neck
  • low-set ears
  • swollen or puffy hands and feet at birth
  • soft nails that turn upward at the ends when they are older
  • multiple pigmented nevi (colored spots on the skin)
  • obstruction of the lymphatic system during fetal development

Short stature

In most cases, weight and height at birth are below the normal values. A reduced growth rate is usually seen just prior to teenage years. Many individuals with Turner's syndrome are treated with recombinant human growth hormone to alleviate short stature, and this method has shown great potential.

Sexual infantilism

This characteristic is caused by rudimentary ovaries. Sexual ducts and external genital structures appear like in normal females, but very immature. When examined at birth, the gonads are long, pale streaks of tissue devoid of primordial follicles. Early in gestation the gonads appear normal and contain primordial germ cells, but after the third month, numbers become severely reduced and, in most patients oocytes are not present after birth. 

A variety of Somatic abnormalities

Frequently observed abnormalities include:
  • Congenital heart disease, including cardiac valve malformations and narrowing of the aorta
  • Hypothyroidism, due to inadequate secretion of thyroid hormones
  • Skeletal abnormalities leading to dislocations of the patella, scoliosis and chronic knee pain

Kidney problems 

Kidney problems are present in approximately 1/3 of individuals with Turner’s. These problems may contribute to high blood pressure.

Three types of kidney problems have been reported:
  1. a single horseshoe-shaped kidney, instead of two distinct, bean-shaped structures
  2. an abnormal urine collecting system
  3. an abnormal artery supply to the kidneys

Osteoporosis

There is a high incidence of osteoporosis in Turner’s patients. This is a condition characterized by thin or weak bones, which can lead to loss of height, curvature of the spine and increased bone fractures. The primary cause of osteoporosis in individuals with Turner’s appears to be inadequate circulating estrogen in the body. 

Intelligence

Normal intelligence is a common characteristic in individuals with Turner's syndrome, but a majority have some type of learning disability, often involving visual-spatial skills.

Clinical Abnormalities and Approximate Incidence

Short Stature

100%

Ovarian Failure

90%

Puffy hands and feet

80%

Broad chest

80%

Low posterior hairline

80%

Unusual shape and rotation of ears

80%

Small lower jaw

70%

Inner canthal folds

70%

Arms turned out slightly at elbows

70%

Soft upturned nails

70%

Kidney anomalies

60%

Shortened 4th digit

50%

Webbed neck

50%

Pigmented nevi (small brown moles)

50%

Cardiac anomalies

50%

Hearing loss

50%

Narrow, high-arched palate

40%

Premature menopause issue  

Since the X chromosomes dictate female physical characteristics, the missing genes interfere with sexual development. The worst possible complication is infertility, caused by the failure of the ovaries to grow properly. A great majority of patients undergoes a premature menopause at that point. There may be some eggs present at birth but these degenerate soon after. Unfortunately, only about 5 to 10 percent of girls with Turner’s syndrome menstruate naturally; all the rest need hormone replacement therapy.

Prenatal diagnosis

Turner's syndrome is commonly diagnosed prenatally. It also happens often in women undergoing amniocentesis or chorionic villus sampling for other reasons. Advanced maternal age does not seem to be a risk factor for this disorder by itself.

Ultrasonography  

Ultrasonography is one very valuable tool for detecting fetuses with Turner's syndrome.

Typical findings include:
  • a thickened neck
  • edema of the hands and feet
  • renal or left-side cardiac abnormalities
Other tests
  • Clinical history
  • Physical examination
  • Psychological and educational assessment
  • Blood tests and chromosome analysis
  • Genetic tests

Treatment options

Turner’s syndrome is a lifelong condition, but there are many treatment options that can for help affected women reach their potential in all aspects of life. The goal of treatment is to correct physical defects and help bring about puberty.

Most common treatments are:
  • Hormone replacement therapy to speed up or to trigger menstruation and the development of secondary sexual characteristics such as breasts
  • Surgery to correct possible present heart defects
  • Growth hormone therapy to increase height
  • Regular monitoring to check hormone levels
  • Regular follow-up and management of underlying medical conditions
  • Treatment for the management of complications such as high blood pressure
  • Assisted reproduction

Medical consequences of Turner syndrome

Cardiovascular problems: Research has shown a significantly greater number of deaths from diseases of the circulatory system than expected. Almost half of them are due to congenital heart disease. Cardiovascular malformations are a serious concern, as it is the most common cause of death in adults with Turner’s syndrome.

Thyroid problems: Approximately 1/3 of individuals with Turner’s syndrome have a thyroid disorder, most commonly hypothyroidism.

Symptoms of this condition include:
  • decreased energy
  • dry skin
  • cold-intolerance
  • poor growth
  • overweight
In most cases, this disorder is caused by an immune system attack on the thyroid gland. This type of thyroiditis is also known as Hashimoto's thyroiditis. Although it is not known why thyroid disorders occur with a high frequency in Turner’s syndrome, the condition is easily treated with thyroid hormone supplements.

Type II diabetes

Type II diabetes, also known as insulin-resistant diabetes, has a high occurrence rate in individuals with Turner’s syndrome. Patients who suffer from this syndrome have twice the risk of the general population for developing this disease. Unfortunately, the reason for the increased risk of diabetes is unknown. Diabetes type II can be controlled through careful monitoring of blood-sugar levels, diet, exercise, and medication.