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Turner syndrome

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Turner syndrome is a genetic condition that occurs when one of a girl's X chromosomes is either missing or altered. This condition can be diagnosed by looking at a karyotype (chromosomal analysis). It was discovered by Dr. Henry Turner in 1938. About 1 in every 2000 to 2500 girls have Turner syndrome.[1] The main symptoms of Turner syndrome include short stature and a lack of sexual development. It also can cause several health complications such as heart problems, diabetes, osteoporosis, and ear infections.

Cause and Types

Karyotype of a girl with monosomy X

People generally have forty-six chromosomes, two of which are sex chromosomes. For females, these are the two X chromosomes. In Turner syndrome, one of these X chromosomes is either altered or absent.[2] One common form of Turner syndrome, which occurs in about 50% of girls with the disorder, is monosomy. Monosomy happens when an X chromosome is completely missing, often because of nondisjunction, which is when the sex chromosomes don't pull apart in the sperm or egg, preventing it from passing on an X chromosome.[3][1]

Sometimes, a mistake will occur while the cells are dividing. In this case, some cells will be unaffected and have two normal X chromosomes, but others will have only one normal X chromosome.[4] This is known as mosaicism, and it occurs in about 30% of girls with Turner syndrome.For about 20% of girls affected by Turner syndrome, there are two X chromosomes, but one has been altered, and could be ringed-shaped or missing parts.[1] In a few cases, there is even some Y chromosome material present.[4] Scientists aren't exactly sure which genes cause which features of Turner syndrome. However, they know that the reason girls with Turner syndrome are short in stature is that they lack a copy of the SHOX gene, which is involved in the growth of bones.[3]

Symptoms and Characteristics

One of the main symptoms in Turner syndrome is short stature, as shown by this growth chart

There are several different symptoms of Turner syndrome. One major characteristic of this disorder is that people affected by it are usually short in stature compared to other girls. They have a very slow rate of growth during childhood and achieve an average adult height of only 4 feet 8 inches.[5] Turner syndrome causes the ovaries of most affected girls not to work. This means that the ovaries cannot produce the hormone estrogen. Because of this, the girl will not go through normal puberty, and usually cannot have children.[6] Sometimes a girl with Turner syndrome will have menstrual cycles, but they normally end when she is in her 20s.[5]

Some physical characteristics include a high, narrow palate, a receding jawline, low-set ears, a lower than normal hairline, fingernails or toenails that are turned upwards, and dark spots on the face called pigmented nevi.[4][5] At birth, a girl with Turner syndrome will often have a shorter than average birth length and swelled up or puffy hands or feet, called lymphedema.[4][3] Many of them have difficulty with fine motor skills, nonverbal learning, and spacial related problems, such as those found in math.[4][6] However, their intelligence is not usually lower than average. They may also struggle in social situations that require them to comprehend the feelings and behavior of others.[4]

Health Issues

Turner syndrome can cause several health complications. For instance, almost half of people with Turner syndrome have problems with the heart or with a major blood vessel called the aorta.[3][4] This could be aortic dissection, which is a rip inside the aorta, or aorta valve stenosis, when the valve narrows. They also are more likely to have high blood pressure or develop type 2 diabetes than most people.[4][5] Because bones in girls with Turner syndrome often do not develop normally due to a lack of significant amounts of estrogen, a curving of the spine called scoliosis may occur. They also have a higher likelihood of experiencing osteoporosis, a weakening of the bones.

Vision and hearing may also be affected, and there is an increased chance of hearing loss, middle ear infections, and farsightedness, also called hyperopia. There is also a higher risk for a girl with Turner syndrome to suffer from hypothyroidism, which causes the thyroid gland to not produce enough of the hormones that affect metabolism and other processes.[4] This usually occurs when the immune system attacks the thyroid gland in what is called Hashimoto's thyroiditis. Also, in about one third of girls with Turner syndrome, the kidneys are deformed, which can cause urinary infections.[5]

Diagnosis and Treatment

Typically, a girl will be diagnosed with Turner syndrome when she is born or at the time when other girls experience puberty, as these are the times when the symptoms usually become apparent. Normally, the test used for diagnosis is a karyotype. A karyotype is a blood test where in the number and appearance of chromosomes in the nucleus are analyzed. The karyotype allows abnormalities in the chromosomes to be seen.[7] Sometimes Turner syndrome can be diagnosed before birth in what is called prenatal testing. Prenatal screening allows the child's DNA be tested using different methods. A sample of the mother's placenta is taken in chorionic villus sampling. In another process, called amniocentesis, amniotic fluid is used.[4] Other tests used to diagnose Turner syndrome include echocardiograms, MRIs, ultrasounds, and determining how much of the luteinizing and follicle stimulating hormones are present in the blood.[8]

Although the condition itself cannot be cured, some of the symptoms of Turner syndrome can be treated.[9] Regular visits to an endocrinologist, a doctor who specializes in hormones, are important for the treatment of this condition. Injections of growth hormone during childhood can help girls with Turner syndrome to grow taller.[10] Estrogen replacement therapy can help promote sexual development in the girl using the hormones estrogen and progesterone. This also helps prevent osteoporosis. A variety of doctors may be needed to treat other health complications caused by Turner syndrome.[9]

Video

Several women talk about their experience with Turner syndrome

Genetic Disorders

References

  1. 1.0 1.1 1.2 Turner Syndrome Learn.Genetics. Web. Accessed on October 6, 2015.
  2. Turner Syndrome PubMed Health. Web. Accessed on October 6, 2015.
  3. 3.0 3.1 3.2 3.3 Turner syndrome Genetics Home Reference. Web. Published on September 28,2015.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Diseases and Conditions Turner syndrome Mayo Clinic. Web. Accessed on October 6, 2015.
  5. 5.0 5.1 5.2 5.3 5.4 Clinical Features of Turner Syndrome National Institutes of Health. Web. Accessed on October 6, 2015.
  6. 6.0 6.1 Learning About Turner Syndrome National Human Genome Research Institute. Web. Last updated on September 24, 2015.
  7. Turner Syndrome Kids Health. Web. Accessed on October 14, 2015.
  8. Turner Syndrome New York Times. Web. Accessed on October 14, 2015.
  9. 9.0 9.1 What are common treatments for Turner syndrome? National Institute of Child Health and Human Development. Web. Last updated on November 30, 2012.
  10. Turner Syndrome MedicineNet.com. Web. Accessed on October 17, 2015.