What is Turner syndrome (TS)?
Turner syndrome is one of the most common genetic disorders that affects only girls and women. X and Y chromosomes are responsible for determining the sex of an infant. Females are born with two X chromosomes. However, in babies born with TS, one of the X chromosomes is missing or altered.
Turner syndrome is characterized by the common features of short stature, developmental immaturity, webbing of the skin on the neck, and cubitus valgus, where the arms turn out slightly at the elbows.
What are the signs of Turner syndrome?
The main feature of TS is growth failure. Virtually all women with TS grow more slowly than their peers during childhood and adolescence. Delayed puberty and lack of growth spurts results in the average height of adult women with TS being 4 feet 8 inches, unless they are treated with growth hormone. If the person is diagnosed before age 8, growth hormone can be given to help them achieve near-normal height.
Another common feature of those with Turner syndrome is abnormal sexual development. Most affected women will not experience breast development and many will not have menstrual periods. The ovaries of girls with TS are typically small and fibrous and will either function only for a few years or not function at all. Most girls with TS do not go through puberty unless they receive hormone therapy in their late childhood and early teens.
Common physical traits associated with Turner syndrome include:
- Short stature
- Abnormal dental development
- An unusually short, wide neck or webbed neck
- Low hairline at the back of the neck
- Small lower jaw
- Kyphosis (forward rounding of the back)
- Arms that point out at the elbows
Other medical problems are associated with this condition. They include:
- Cardiovascular problems: Up to 50% of those affected will have some sort of cardiac malformation. The most common cardiac problems include bicuspid aortic valve, and elongation of the aortic arch. High blood pressure (hypertension) may also be a problem. All individuals with TS need to undergo a comprehensive cardiac exam at the time of diagnosis.
- Developmental delay and learning disabilities: Overall intellectual function is normal but girls with Turner syndrome tend to have difficulties in visual motor and visual spacial skills.
- Bone disease: Scoliosis develops in about 20% and kyphosis develops in about 50%. An increased risk for fracture and osteoporosis will be present in women who have not been treated with estrogen. And the bone density test typically overestimates the risk for osteoporosis in women who have short stature. Therefore adequate intake of calcium and vitamin D along with active lifestyle is essential.
- Vision problems: Nearsightedness is the most common problem.
- Hearing and ear problems: Malformation of the ears and middle ear infections that can result in conductive hearing loss are more common in girls with Turner syndrome. Sensorineural hearing loss develops in more than 50% of adult TS patients.
- Kidney defects: Congenital malformations of the kidney-urinary system is present in approximately 30-40% of patients. Obstructions of urine flow can result in kidney infections and associated problems.
- Metabolic syndrome: Patients with TS are at high risk for developing obesity, insulin resistance, high blood pressure, high cholesterol, high triglycerides, and type 2 diabetes.
- Autoimmune disorders: The most common disorders seen in TS patients are hypothyroidism, Celiac disease, and inflammatory bowel disease.
What causes Turner syndrome?
Turner syndrome occurs when one of the two X chromosomes that are typically present in the cells of females is missing or incomplete. Although TS is a genetic disorder, generally it is not inherited.
About 45% of girls and women with TS have a form of the disorder in which each cell only has one X chromosome instead of two. This type of TS is called monosomy X. It is caused by an error in the formation of reproductive cells (eggs or sperm) in one of the girl’s parents. During cell division, the egg or sperm may lose an X chromosome. This defect will be passed on when fertilization occurs.
In about 30% of all cases, girls or women have a pair of X chromosomes in some of the cells of the body, while other cells have only one X chromosome. This condition is called mosaic Turner syndrome or 45,X mosaicism.
Sometimes both X chromosomes are present, but one of them is genetically altered or has partial deletions. This occurs in about 20% of all cases.
In rare cases, TS may be inherited. This type of the syndrome is associated with an incomplete X chromosome.
How common is Turner syndrome?
Turner syndrome occurs in about 1 in every 2,500 female babies throughout the world.
How is Turner syndrome diagnosed?
Physical features such as short stature and other characteristics may be the first indication of Turner syndrome. Female infants with TS may show certain features soon after birth, such as swollen hands or feet, or webbing of the skin on the neck. Parents may notice that their girl has stopped growing or is much shorter than her peers. The lack of breast development or menstrual periods at the time when most girls are going through puberty are other signs. A genetic test called a karyotype analysis is needed to definitely diagnose TS. The test will determine whether one of the X chromosomes is missing or partially missing. A small sample of blood is required for the karyotype test.
Some women are not diagnosed with Turner syndrome until they reach adulthood. These women do go through puberty and have menstrual periods, but are likely to have early ovarian failure.
Turner syndrome may be diagnosed when an older pregnant woman undergoes prenatal genetic screening. A karyotype analysis may be performed on a sample of fluid removed during amniocentesis or chorionic villous sampling. However, the chance of having a baby with TS does not increase with the age of the mother.
An ultrasound test may also show that a fetus has some physical features associated with TS, such as heart defects or the presence of lymph fluid around the neck.
How is Turner syndrome treated?
A girl with Turner syndrome should be evaluated and monitored by a pediatric endocrinologist, who can provide suggestions on treating hormone deficiencies. Parents should keep careful growth charts and be aware of other medical problems that may affect girls with TS.
- Human growth hormone: Girls with TS may be treated with synthetic human growth hormone injections to increase their height. The final height of girls who are treated with growth hormone may be increased by several inches if treatment begins in early childhood.
Hormone replacement therapy: In most cases, girls with TS require estrogen (a female hormone) to start developing breasts, normalize uterine size, and begin menstruating during puberty. The goal of estrogen replacement also is for better brain development, cardiovascular function and liver function.
- Androgens:Androgens are male hormones that are produced in boys and girls. The adrenal glands begin to produce androgens when girls are around 8 to 9 years old. The ovaries produce more androgens when girls go through puberty. These hormones cause the growth of hair under the arms and in the genital area and result in a growth spurt. A low dose of androgen along with growth hormone may increase growth in girls with TS without causing undesirable side effects.
Girls and their parents should discuss when to begin estrogen therapy, because high estrogen replacement usually stops bone growth in the late teenage years. After girls who are taking estrogen begin to menstruate, progesterone is added to maintain their regular menstrual cycles.
Women with Turner syndrome are usually infertile. However, sometimes they may be able to become pregnant via special fertilization techniques.
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