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.
Turner 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.
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 1-2% 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.
Signs and symptoms
Turner syndrome is characterized by delayed 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 non-insulin 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
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.
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 mother's age and risk of Turner syndrome.
Treatment and management
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.
Most women with Turner syndrome can live relatively normal lives. The prognosis for people 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.
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Jones, K.L. "XO Syndrome." In Smith's Recognizable Patterns of Human Malformation. Edited by Kenneth L. Jones and Judy Fletcher. 5th ed. Philadelphia: W.B. Saunders, 1997, pp. 81-87.
Plumridge, D. Good Things Come in Small Packages: The Whys and Hows of Turner Syndrome. Portland, OR: University of Oregon Health Sciences Center, 1987.
Reiser, P.A., and L.E. Underwood. Turner Syndrome: A Guide for Families. Wayzata, MN: Turner Syndrome Society, 1992.
Gravholt, C.H., et al. "Morbidity in Turner Syndrome." Journal of Clinical Epidemiology 51, no. 2 (February 1998): 147-158.
Gravholt, C.H., et al. "Prenatal and Postnatal Prevalence of Turner's Syndrome: A Registry Study." British Medical Journal 312, no. 7022 (January 6, 1996): 16-21.
Zinn, A.R., D.C. Page, and E.M. Fisher. "Turner Syndrome: The Case of the Missing Sex Chromosome." Trends in Genetics 9 (1993): 90-93.
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. email@example.com.
Human Growth Foundation. 997 Glen Cove Ave., Glen Head, NY 11545. (800) 451-6434. Fax: (516) 671-4055. <http://firstname.lastname@example.org>.
MAGIC Foundation for Children's Growth. 1327 N. Harlem Ave., Oak Park, IL 60302. (708) 383-0808 or (800) 362-4423. Fax: (708) 383-0899. email@example.com. <http://www.magicfoundation.org/ghd.html>.
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>.
Turner Syndrome Society of the United States. 14450 T. C. Jester, Suite 260, Houston, TX 77014. (800) 365-9944 or (832) 249-9988. Fax: (832) 249-9987. firstname.lastname@example.org. <http://www.turner-syndrome-us.org>.
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>.
L. Fleming Fallon, Jr., MD, PhD, DrPH