Turner syndrome is a birth defect caused by the absence of an X chromosome in some or all cells of a female, which inhibits sexual development and usually causes infertility.
Chromosomes are structures in the nucleus of every cell in the human body that contain the genetic information necessary to direct the growth and normal functioning of all cells and systems of the body. A normal individual has a total of 46 chromosomes in each cell, two of which are responsible for determining gender. Normally, females have two X chromosomes, and males have one X and one Y chromosome.
In Turner syndrome, an error occurring very early in development results in an abnormal number and arrangement of chromosomes. Most commonly, an individual with Turner syndrome will be born with 45 chromosomes in each cell rather than 46. The missing chromosome is an X chromosome. The affected person is always female.
Turner syndrome may result in a wide spectrum of symptoms, from major heart defects to minor cosmetic issues. Some individuals with Turner syndrome may only have a few symptoms while others may have many. Almost all girls with Turner syndrome have short stature and loss of ovarian function, but the severity of the symptoms varies among individuals.
Turner syndrome is also referred to as Bonnevie-Ullrich syndrome, gonadal dysgenesis, and monosomy X.
The prevalence of Turner syndrome is widely reported as being approximately one per 2,500 live female births, although researchers have reported prevalence rates that range from one in 3,125 to one in 5,000 live female births. About 1 to 2 percent of all female conceptions have a missing X chromosome. Of these, the majority (99%) spontaneously abort, usually during the first trimester of pregnancy.
Causes and symptoms
Turner syndrome usually occurs sporadically, which means that the mutation occurs during fetal development and is not inherited from either parent. In rare cases, a parent may carry rearranged chromosomes that can result in Turner syndrome in a daughter, which is the only situation in which the Turner syndrome is inherited.
More than half of all girls with Turner syndrome are mosaics, which means that the mutation occurs in some but not all cells of their body. Therefore, Turner syndrome can vary in severity. The fewer the affected cells, the milder the disease.
Symptoms of a girl with Turner syndrome include:
- short stature
- webbed skin of the neck
- abnormal eye features (drooping eyelids)
- abnormal bone development, such as a "shield-shaped," broad flat chest
- absent or retarded development of secondary sexual characteristics that normally appear at puberty , including sparse pubic hair and small breasts
- coarctation (narrowing) of the aorta
- bicuspid aortic valve
- dry eyes
- absence of menstruation
Growth in children with Turner syndrome is characterized by a slight intrauterine growth retardation , relatively normal growth rates for the first several years of life, a progressive deceleration of growth later in childhood, and the lack of a pubertal growth spurt. The average height of Turner women is 147 cm (57.8 inches), varying between 135 (53 inches) and 163 cm (64 inches). This is about 20 cm (7.8 inches) shorter than the height of women with normal chromosomes.
Normal pubertal development and spontaneous menstrual periods do not occur in the majority of children with Turner syndrome. Most girls with Turner syndrome do not have ovaries with healthy oocytes capable of fertilization and embryo formation. However, it is estimated that 3 to 8 percent of girls with a single X chromosome and 12 to 21 percent of females with sex chromosome mosaicism may have normal pubertal development and spontaneous menstrual periods. A few pregnancies have been reported in women with Turner syndrome.
Individuals with Turner syndrome report an increased incidence of fractures in childhood and osteoporotic fractures in adulthood. The primary cause of osteoporosis may be inadequate levels of estrogen circulating in the body; however, defects in bone structure or strength may also be related to the loss of unknown X-chromosome genes.
The incidence of type II diabetes, also known as insulin resistant diabetes (glucose intolerance), has been reported to be increased in Turner syndrome, with individuals having twice the risk of the general population for developing this disease. The muscles of many persons with Turner syndrome fail to use glucose efficiently, which may contribute to the development of high blood sugar.
Many women with Turner syndrome have high blood pressure, which may even occur during childhood. High blood pressure may be due to aortic constriction or to kidney abnormalities; however, in a majority of cases, no specific cause for high blood pressure can be identified.
Kidney problems are present in about one third of girls with Turner syndrome and may contribute to high blood pressure. Three types of kidney problems have been reported: the presence of a single horse-shoe shaped kidney (normally two distinct, bean-shaped structures are present); an abnormal urine-collecting system; or an abnormal artery supply to the kidneys.
From 5 to 10 percent of girls with Turner syndrome have a severe constriction of the major blood vessel coming from the heart ( coarctation of the aorta ). This defect is thought to be a result of an obstructed lymphatic system compressing the aorta during fetal development. Other major defects and its major vessels are reported to a lesser degree. As many as 15 percent of children with Turner syndrome have bicuspid aortic valves, where the major blood vessel from the heart has only two rather than three components to the valve regulating blood flow.
Juvenile rheumatoid arthritis, an autoimmune condition, has been associated with Turner syndrome. The prevalence seems to be at least six times greater than would be expected if the two conditions were only randomly associated. Girls with Turner syndrome have an elevated prevalence rate of dental caries and such other periodontal conditions as gum disease and plaque.
Approximately one-third of girls with Turner syndrome have a thyroid disorder, usually hypothyroidism . Symptoms of this condition include decreased energy, dry skin, cold-intolerance, and poor growth.
Contrary to earlier reports, most individuals with Turner syndrome are not mentally retarded. They may have some learning disabilities, particularly with regard to spatial perception, visual-motor coordination, and mathematics. This specific learning problem is referred to as Turner neurocognitive phenotype and appears to be due to loss of X chromosome genes important for selected aspects of nervous system development. The verbal skills of girls with Turner syndrome are usually normal. Some girls with Turner syndrome may also have difficulties with memory and motor coordination, which may be related to estrogen deficiency.
When to call the doctor
Parents should call their healthcare provider if their infant has symptoms of this disorder or if an adolescent girl's sexual development appears to be delayed.
Turner syndrome is either diagnosed at birth because of associated anomalies or at puberty when there is absent or delayed menses and delayed development of normal secondary sexual characteristics. During a physical examination, the doctor looks for underdeveloped breasts and genitalia, webbed neck, short stature, low hairline in back, simian crease (a single crease in the palm), and abnormal development of the chest. An ultrasound may reveal small or undeveloped female reproductive organs while a gynecologic examination may reveal a dry vaginal lining. A kidney ultrasound can be used to evaluate abnormalities of the kidneys. After diagnosis, echocardiogram (heart ultrasound) and an MRI of the chest are performed to evaluate possible cardiac defects.
Hands and feet of infants with Turner syndrome may be swollen or puffy at birth; there may be swelling at the nape of the neck. These babies often have soft nails that turn upwards on the ends when they are older. These features appear to be due to obstruction of the lymphatic system during fetal development. Another characteristic cosmetic feature is the presence of multiple pigmented nevi (colored spots on the skin).
Turner syndrome is confirmed on the basis of genetic analysis of chromosomes, which can be done prior to birth. However, the predictive value of amniocentesis in diagnosing Turner syndrome varies from 21 to 67 percent. There is no significant relation between the mother's age and risk of Turner syndrome.
Most individuals with Turner syndrome require female hormone therapy to promote development of secondary sexual characteristics and menstruation. The time of beginning therapy varies with individuals. Experts recommend that therapy begin when a woman expresses concern about her onset of puberty or by the age of 15. Girls and women with Turner syndrome should be treated with estrogen/progesterone to maintain their secondary sexual development and to protect their bones from osteoporosis until at the least the usual age of menopause (50 years). The use of estrogen therapy may also improve memory and motor coordination problems associated with estrogen deficiency. Assisted reproductive technology may allow for women with Turner syndrome to become pregnant with donated ooctyes.
All women receiving long-term, female hormone therapy require periodic gynecological examinations, because those with Turner syndrome have an increased risk of developing neoplasms, such as gonadoblastoma and dysgerminoma, which arise from their rudimentary streak gonads (a condition in which germ cells are absent and the ovary is replaced by a fibrous streak).
Because it is so dangerous, experts suggest early screening and surgery for aortic coarctation of the artery in girls with Turner syndrome. Bicuspid aortic valves can deteriorate or become infected, so it is advised that
Plastic surgery to correct webbing of the neck should be considered at an early age (before entering school) for girls with Turner syndrome.
Final adult height in individuals with Turner syndrome can be increased if growth hormone (GH) treatment is given relatively early in childhood. However, not all individuals get a good growth response to GH.
Most children with Turner syndrome can live relatively normal lives. The prognosis for a person with Turner syndrome is dependent on the other associated conditions that may be present. Care must be taken to regularly monitor patients for the health problems that are associated with Turner syndrome. For example, heart or kidney defects may significantly impact their quality of life. Without these types of conditions, however, their life expectancy is normal. Support will be necessary to help an adolescent girl cope with body image issues and to help some women accept the fact that they will never be able to have children.
Families may wish to seek counseling regarding the effects of the syndrome on relationships within the family . Many people respond with guilt, fear , or blame when a genetic disorder is diagnosed in the family, or they may overprotect the affected member. Support groups are often good sources of information about Turner syndrome; they can offer helpful suggestions about living with it as well as emotional support.
Bicuspid aortic valve —A condition in which the major blood vessel from the heart has only two rather than three components to the valve regulating blood flow.
Coarctation of the aorta —A congenital defect in which severe narrowing or constriction of the aorta obstructs the flow of blood.
Mosaic —A term referring to a genetic situation in which an individual's cells do not have the exact same composition of chromosomes. In Down syndrome, this may mean that some of the individual's cells have a normal 46 chromosomes, while other cells have an abnormal 47 chromosomes.
Ovary —One of the two almond-shaped glands in the female reproductive system responsible for producing eggs and the sex hormones estrogen and progesterone.
All about Me: Growing Up with Turner Syndrome and Nonverbal Learning Disabilities. Wallington, VT: Maple Leaf Center, 2004.
Roche, Alex F., and Shumei S. Sun. Human Growth: Assessment and Interpretation. Cambridge, UK: Cambridge University Press, 2003.
Turner Syndrome: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, CA: Icon Health Publications, 2004.
Human Growth Foundation. 997 Glen Cove Avenue, Glen Head, NY 11545. Web site: http://www.hgfound.org.
Turner Syndrome Society of the United States. 14450 TC Jester, Houston, TX 77014. Web site: http://www.turner-syndrome-us.org.
Turner Syndrome Support Society (UK). Hardgate, Clydebank, UK. Web site: http://tss.org.uk .
"Turner Syndrome." National Institute of Child Health and Human Development, National Institutes of Health. Available online at http://turners.nichd.nih.gov/ (accessed November 15, 2004).
Judith Sims, MS L. Fleming Fallon, MD, PhD, DrPH