Turner syndrome is a genetic disorder that occurs exclusively in girls and results from an abnormality of a chromosome. Chromosomes are material in the cells of the body which contain genes that determine each person's characteristics.
Everyone has 22 pairs of chromosomes in addition to a pair of sex chromosomes, called X and Y. A female has two X chromosomes (referred to as a XX karyotype), and a male has one X and one Y chromosome (XY karyotype).
In Turner syndrome, one of the X chromosomes is missing (XO karyotype) or is structurally abnormal (XX(abnormal)). This results in a variety of physical manifestations (findings) with the most common being short stature.
There is no known cause of why this chromosomal abnormality occurs. Neither parent is responsible for this happening nor can they prevent it.
It is not associated with parental age or environmental factors such as maternal drug abuse, alcohol consumption, medication, cigarette smoking, etc. Parents who have one daughter with Turner syndrome do not have an increased risk of having additional daughters with this syndrome.
The incidence of Turner syndrome is approximately 1:2000 live female births. However, the chromosomal abnormality is actually more common than this as 99% of XO fetuses do not survive beyond 28 weeks gestation, and the XO karyotype occurs in 1 out of 15 miscarriages.
Girls with Turner syndrome may have some normal cells in their body (46,XX) with other cells showing the abnormal karyotype 45, XO or 46, XX(abnormal). These girls are described as Turner mosaics and generally have less manifestations of the syndrome.
The X chromosome contains important genes for traits like stature and ovarian function. Consequently, by having a missing or abnormal X chromosome, girls with Turner syndrome will have findings that relate to what those genes code (for example, short stature and ovarian dysfunction).
There are multiple findings in girls with Turner syndrome and they occur with varying frequencies. Consequently, not all features will necessarily be present in each affected girl. In fact, short stature in many girls may be the only manifestation. A list of the common findings are presented in the Table and discussed in the following sections.
|Characteristic facial features|
|Low posterior hairline|
|Edema of hands/feet|
The most common physical abnormality in girls with Turner syndrome is short stature. This is thought to be primarily a result of an abnormality of the growth response of the skeleton. Affected girls usually show an early decline in their growth within the first few months of life followed by a normal or near normal growth velocity until between 3 and 5 years of age. After 3 to 5 years, growth becomes increasingly abnormal (see Figure) so that the height of a Turner girl falls further and further below the normal curve. The average Turner adult height reached is 4 feet 8 inches, compared to an average adult female height of 5 feet 41/2 inches. There are genetic influences so that Turner girls who have tall parents typically will be taller than the average Turner height and likewise girls with short parents will be shorter.
Figure. Growth curve for girls with Turner Syndrome. (Provided as a service of Genentech, Inc. ď¿½ Genentech, Inc., 1987. All rights reserved.)
Some girls with Turner syndrome have a distinctive facial appearance, and this is due in part to abnormal development of the bones in the face. Characteristic features include a small chin, downward droop of the outer corners of the eyes, and an abnormally arched palate (roof of mouth)
Many girls with Turner syndrome have maldevelopment of their lymphatic system. The lymphatic system is a collection of vessels that bring fluid from body tissues back to the heart. As a result of lymphatic obstruction, there is extra fluid in a Turner fetus referred to as lymphedema. There is often a large collection of fluid in the neck, and when this fluid eventually decompresses, the skin remains stretched and can appear "webbed". The stretching of the neck skin also results in a low posterior hair line, low-set and rotated ears, and extended growth of the eyebrows. Lymphedema of the hands and feet in a Turner fetus may cause abnormal development of fingernails and toenails. If this edema is present in a newborn, there is the appearance of "puffy" hands and feet. This typically resolves within the first few weeks/months after birth.
The ovaries in girls with Turner syndrome initially develop normally in the fetus. However, if there are not two normal X chromosomes in the ovarian cells, there is early egg loss and scarring of the ovaries. This process can occur entirely prenatally or within the first few months or years of life. The ovaries also produce the hormone estrogen which is responsible for sexual development in girls. Consequently, the majority of girls with Turner syndrome do not show spontaneous puberty such as breast development and menstrual periods. Most girls are also infertile.
In approximately 10 to 20% of Turner girls, there will be some ovarian function at puberty that allows for a little bit of breast development. A small percent of this group will also have normal periods, and an even smaller percent (less than 1% of all girls with Turner syndrome) will actually be fertile. Pregnancy has been reported in a small number of girls with Turner syndrome; however, there is an increased risk of chromosomal abnormalities in the children of these women. Girls who are Turner mosaic have a greater chance of retaining some or all of their ovarian function.
There is an increased risk of heart abnormalities in Turner girls. Coarctation of the aorta is a condition where there is a narrowing of the aorta (the main blood vessel coming from the heart). This occurs in 15 to 20% of Turner girls and is more common in girls with a webbed neck. If found, this abnormality requires surgical treatment. A more common abnormality that occurs in up to 30% of girls is a bicuspid aortic valve. The normal valve of the aorta has three leaflets whereas a bicuspid valve only has two. Girls with bicuspid valves need cardiology follow-up but do not require surgical repair. High blood pressure may also occur in Turner girls but is not typically evident until adulthood. There is also a risk of dilation of the aorta that if not diagnosed and treated can rupture and cause significant morbidity and/or mortality. It is not clear whether girls who have normal hearts are at risk for dilation of the aorta or if it only occurs in those with abnormal hearts (i.e., coarctation or bicuspid valve). Because of this uncertainty, it is the opinion of this author that girls with normal hearts have a cardiology evaluation every 4-5 years.
Kidney abnormalities occur in 30-40% of girls with Turner syndrome. These abnormalities typically involve the structure, position, or blood vessels of the kidneys. Usually there are no health consequences of these abnormalities. Rarely patients require surgery or have any kidney impairment.
One of the most common medical problems in girls with Turner syndrome is recurrent ear infections. Abnormal development of the bones of the face leads to an abnormal relationship between the middle ear and eustation tube, which creates a predisposition to fluid collection in the middle ear and infection. Hearing loss may be a consequence of recurrent ear infections and fluid in the middle ear. This is referred to as conductive hearing loss.
Hearing loss that is not associated with ear infections (referred to as sensorineural hearing loss) also occurs in a high percentage (about 64%) of Turner girls. This hearing loss can become worse with age; consequently, girls with Turner syndrome should have regular assessments of their hearing.
Other disorders that are seen with increased frequency in girls with Turner syndrome include hypothyroidism and gastrointestinal disorders. Diabetes mellitus may also occur but generally not until adolescence or adulthood.
The intelligence of girls with Turner syndrome is normal; however, there is often impairment in motor skills, visual-motor coordinating, and visualizing objects in relation to each other. This type of impairment is termed nonverbal learning disability (NVLD), often manifested by a discrepancy between verbal and performance IQ scores with verbal scores being higher.
Girls with Turner syndrome and NVLD have difficulty with mathematics, tasks requiring manual dexterity, and poor directional sense (i.e., difficulty with left and right). These girls may also show social immaturity as they have difficulty understanding social and nonverbal cues.
These neuro-psychological findings are seen in a high percentage of, but not all Turner girls. Consequently, it may be beneficial for girls to have neuro-psychological testing early on so parents and teachers can help girls compensate for this problem.
A girl who has the clinical findings suggestive of Turner syndrome should have a chromosomal analysis done by a simple blood draw. The blood is sent to a laboratory where specialists separate the chromosomes in the white blood cells and count and examine them carefully.
Since poor growth may be the only finding in many girls with Turner syndrome, this test should be strongly considered in any girl who has unexplained short stature.
Once the diagnosis of Turner syndrome has been established by chromosome analysis, additional studies and tests are indicated. Because of the risk of hypothyroidism, thyroid tests should be done on a yearly basis.
In girls who are older than 10 years, blood studies can also be done to assess for ovarian function. An ultrasound of the kidney allows for detection of any abnormality. If this study is normal, it does not need to be repeated.
A cardiology consultation should be obtained in all girls, and part of this evaluation generally includes an echocardiogram (ultrasound of the heart). Girls with Turner syndrome should also be referred to a pediatric endocrinologist as soon as the diagnosis is made.
Growth hormone therapy has been shown in several studies to increase final height in girls with Turner syndrome by up to 3-4 inches. Turner syndrome is one of the three FDA approved indications for growth hormone treatment in children.
At this time, growth hormone therapy should be considered as soon as a Turner girl has dropped below the fifth percentile of the normal female growth curve.
Growth hormone is safe and has only a few rare adverse side effects. A pediatric endocrinologist monitors girls on growth hormone therapy every 3-4 months for response and possible side effects. Currently, patients receive growth hormone as a daily subcutaneous injection (just under the skin).
In girls who have ovarian failure, estrogen is started sometime between ages 12 and 14 years to allow for pubertal development. Progesterone (another important hormone that the ovary makes) is typically added 1 to 2 years after estrogen is started. Both of these hormones can be taken orally as tablets; estrogen is also available as a patch preparation.
Although the majority of Turner girls are infertile, they can be the recipient of an embryo (donated egg which is fertilized in vitro) and can carry a pregnancy successfully to term.
Other treatments are indicated according to the clinical findings, i.e., hypothyroidism, heart abnormalities, etc.
There is currently a national multi-center study giving growth hormone to toddler girls (ages 9 months to 4 years) to see if it can prevent the early fall off in growth that girls with Turner's syndrome have. Frequency of ear infections, and hearing and development assessments are also monitored in this study. The Turner's Syndrome Society web site has information on this study and others.
Lippe BM: Turner Syndrome. In Sperling MA (ed): Pediatric Endocrinology. Philadelphia, WB Saunders, 1996, pp. 387-421.
Rosenfeld RG, Attie KM, Frane J, et al: Growth hormone therapy of Turner's syndrome: Beneficial effect on adult height. J Pediatr 132:319, 1998.
Rosenfeld RG, Tesch LG, Rodriguez-Rigau LJ, et al: Recommendations for diagnosis, treatment, and management of individuals with Turner syndrome. The Endocrinologist 4:351. 1994.
About the Author
Dr. Travers is an Assistant Professor of Pediatrics at the University of Colorado Health Sciences Center. She is board certified in both Pediatrics and Pediatric Endocrinology.
She is a clinician at The Children's Hospital of Denver and sees children with a variety of endocrine disorders. Her clinical and research interests include Turner Syndrome and obesity in childhood.
Copyright 2012 Sharon H. Travers, M.D., All Rights Reserved