Turner syndrome

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Turner Syndrome

 

Definition

Turner syndrome is a chromosomal disorder affecting females wherein one of the two X-chromosomes is defective or completely absent.

Description

Chromosomes are structures in the nucleus of every cell in the human body. Chromosomes 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.
The prevalence of Turner syndrome is widely reported as being approximately one per 2,000 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% of all female conceptions have a missing X-chromosome. Of these, the majority (99%) spontaneously abort, usually during the first trimester of pregnancy. With ultrasound being used more frequently, researchers have realized that some pregnancies with a missing X-chromosome that progress into the second trimester are associated with nuchal cysts, severe lymphedema, or hydrops fetalis. These pregnancies are associated with a high frequency of fetal death.

Causes and symptoms

Turner's syndrome is a disorder associated with characteristic defects in the X-chromosome. The most common presentation is a female with a single X-chromosome and an absent X-chromosome. A Greek study from 1999 reported that the intact X-chromosome was as likely to come from the mother as from the father. This means that there is no parental pattern of responsibility for the missing or defective X-chromosome.
Another less common genetic pattern for Turner Syndrome (35%) is a mosaic. A Danish study reported that mosaicism has an effect on malformations that are associated with Turner syndrome. Research reported in 1997 noted that the karyotype can have a significant effect on the growth of children with Turner syndrome.
The exact location of the genes on the X-chromosome involved in Turner syndrome has not been determined as of 2001. At present, evidence exists that there is a locus for stature on the distal portion of the short arm; there are loci for normal ovarian function on both the short and long arms; and there are loci contributing to fetal viability on the long arm of X.
Turner syndrome is characterized by retarded growth that leads to a small stature and frequent infertility. Individuals with Turner syndrome report an increased incidence of fractures in childhood and osteoporotic fractures in adulthood. The incidence of diabetes mellitus (both insulin dependent and noninsulin dependent varieties) has been reported to be increased in Turner syndrome. Ischemic heart disease, stroke and hypertension are also more common.
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. Growth patterns of Chinese girls with Turner syndrome parallel those of Caucasians, although their ultimate height is still less than normal.
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. As a result, the nonverbal IQ in Turner syndrome tends to be lower than the verbal IQ.
Cardiovascular malformations are well-recognized congenital anomalies in Turner syndrome. Dilation and dissection of the aorta are reported in approximately half of women with Turner syndrome. Because of the potential consequences of aortic dilation, some experts recommend screening all individuals with Turner syndrome. However, the specific timing for this screening remains controversial in 2001.
Juvenile arthritis, an autoimmune condition, has been recently (1998) 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. Women with Turner syndrome have an elevated prevalence rate of dental caries and such other periodontal conditions as gum disease and plaque.
Normal pubertal development and spontaneous menstrual periods do not occur in the majority of children with Turner' syndrome. It is estimated that 3-8% of girls with a single X-chromosome and 12-21% 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.

Diagnosis

Turner syndrome is diagnosed on the basis of genetic analysis of chromosomes. This can be done prior to birth. However, the predictive value of amniocentesis in diagnosing Turner syndrome varies from 21-67%. There is no significant relation between the mother's age and risk of Turner's syndrome.

Treatment

Because it is so dangerous, experts suggest screening for aortic dissection, although the specific timing for this screening is controversial. Plastic surgery to correct webbing of the neck should be considered at an early age (before entering school) for girls with 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.
All women receiving long-term, exogenous 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.

Prognosis

Most women with Turner syndrome can live relatively normal lives. The prognosis for a person with Turner syndrome is dependent on other conditions that may be present. Care must be taken to regularly monitor them for the health problems that are associated with Turner syndrome. For example, heart or kidney defects, hearing loss, or the development of inflammatory bowel disease may significantly impact the 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.

Key terms

Chromosome — A microscopic thread-like structure found within each cell of the body that consists of a complex of proteins and DNA. Humans have 46 chromosomes arranged into 23 pairs. Changes in either the total number of chromosomes or their shape and size (structure) may lead to physical or mental abnormalities.
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 — The female reproductive organ that produces the reproductive cell (ovum) and female hormones.
Zygote — The cell formed by the uniting of egg and sperm.

Resources

Books

Hall, Judith G. "Chromosomal Clinical Abnormalities." In Nelson Textbook of Pediatrics, edited by Richard E Behrman, et al., 16th ed. Philadelphia: W.B. Saunders, 2000, pp. 325-334.

Organizations

American Academy of Pediatrics. 141 Northwest Point Blvd., Elk Grove Village, IL 60007-1098. (847) 434-4000. Fax: (847) 434-8000. http://www.aap.org/visit/contact.htm.
Endocrine Society. 4350 East West Highway, Suite 500, Bethesda, MD 20814-4410. (301) 941-0200. Fax: (301) 941-0259. endostaff@endo-society.org.
Human Growth Foundation. 997 Glen Cove Ave., Glen Head, NY 11545. (800) 451-6434. Fax: (516) 671-4055. http://www.hgfound.org.
Turner Syndrome Society of Canada. 7777 Keele St, Floor 2, Concord, ONT L4K 1Y7. Canada (800) 465-6744 or (416) 660-7766. Fax: (416) 660-7450.
Turner Syndrome Society of England. 2 Mayfield Ave., London, W41PW. UK 44 (0)181-994 7625. Fax: 44 (0)181-995 9075. http://www.exnet.com/staff/sys4/ts.html or http://www.tss.org.uk.

Other

American Academy of Pediatrics. http://www.aap.org/visit/contact.htm.
On-ramp Access. http://www.onr.com/ts-texas/turner.html.
Turner Syndrome Support Society(UK). http://www.tss.org.uk/.
University of Kansas Medical Center. http://www.kumc.edu/gec/support/turner.html.

Tur·ner syn·drome

(tŭr'nĕr),
a syndrome with chromosome count 45 and only one X chromosome; buccal and other cells are usually sex chromatin-negative; anomalies include dwarfism, webbed neck, valgus of elbows, pigeon chest, infantile sexual development, and amenorrhea; the ovary has no primordial follicles and may be represented only by a fibrous streak; some affected people are chromosomal mosaic, with two or more cell lines of different chromosome constitution; seen in many animal species, in the meadow vole it is the normal female state.
Synonym(s): XO syndrome

Tur·ner syn·drome

(tŭr'nĕr),
a syndrome with chromosome count 45 and only one X chromosome; buccal and other cells are usually sex chromatin-negative; anomalies include dwarfism, webbed neck, valgus of elbows, pigeon chest, infantile sexual development, and amenorrhea; the ovary has no primordial follicles and may be represented only by a fibrous streak; some affected people are chromosomal mosaic, with two or more cell lines of different chromosome constitution; seen in many animal species, in the meadow vole it is the normal female state.
Synonym(s): XO syndrome

Turner syndrome

(tûr′nər) also

Turner's syndrome

(-nərz)
n.
A congenital condition of girls and women caused by complete or partial absence or deficiency of one X chromosome, characterized by short stature, a webbed neck, low-set ears, skeletal abnormalities, and infertility owing to ovarian failure.

Turner syndrome

Gonadal dysgenesis, monosomy X, XO female Genetics A condition characterized by an XO chromosome pattern in a phenotypic ♀ with pathognomonic Sx Clinical Absent ovaries–gonadal agenesis or dysgenesis, short stature, webbed neck, rarely, mental retardation Variants A second X may be present, but partially deleted; in mosaics, some cells are 45,X and others 46,XX Treatment Female sex hormone at puberty to induce adult appearance and menses; most XOs are sterile

Turn·er syn·drome

(tŭr'nĕr sin'drōm)
A syndrome with chromosome count 45 and only one X chromosome; buccal and other cells usually test negative for sex chromatin; anomalies include dwarfism, webbed neck, valgus of elbows, pigeon chest, infantile sexual development, and amenorrhea; the ovary has no primordial follicles and may be represented only by a fibrous streak; some patients are chromosomally mosaic, with two or more cell lines of different chromosome constitution; seen in many animal species; in the meadow vole, it is the normal female state.
Synonym(s): XO syndrome.

Turner,

Henry H., U.S. endocrinologist, 1892-1970.
Turner syndrome - a syndrome with chromosome count 45 and only one X chromosome. Synonym(s): XO syndrome

Turn·er syn·drome

(tŭr'nĕr sin'drōm)
A syndrome with chromosome count 45 and only one X chromosome; buccal and other cells usually test negative for sex chromatin; anomalies include dwarfism, webbed neck, valgus of elbows, pigeon chest, infantile sexual development, and amenorrhea.
Synonym(s): XO syndrome.
References in periodicals archive ?
G-banding with trypsin treatment and Giemsa stain (GTG-banded) chromosome analysis showed a mosaic karyotype with two cell lines: five cells with a 45,X karyotype and 15 cells with a 46,XY karyotype.