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Turner syndrome is a disorder of the sex chromosomes. Humans usually have 23 pairs of chromosomes-thin strands of DNA-in the nucleus of every
cell, which contain genes that determine our hereditary makeup. One pair of chromosomes is the sex chromosomes, designated X and Y. Females
usually have two X chromosomes; however, patients with Turner syndrome have only a single X chromosome or one normal and one defective X or Y
chromosome. This abnormality can cause medical problems such as short stature, premature ovarian failure and heart or kidney defects. Individuals
with Turner syndrome have an increased risk of thyroid disorders, high blood pressure, diabetes mellitus, abnormal liver function, hearing loss and
Clinical Features of Turner Syndrome
Turner syndrome affects approximately 1 out of every 2,500 female live births worldwide. It embraces a broad spectrum
of features, from major heart defects to minor cosmetic issues. Some individuals with Turner syndrome may have only
a few features, while others may have many. Almost all people with Turner syndrome have short stature and loss of
ovarian function, but the severity of these problems varies considerably amongst individuals.
Some individuals with Turner syndrome have a short neck with a webbed appearance, a low hairline at the back of the
neck, and low-set ears. Hands and feet of affected individuals may be swollen or puffy at birth, and often have soft nails
that turn upward at the ends when they are older. All these features appear to be due to obstruction of the lymphatic
system during fetal development. Another characteristic cosmetic feature is the presence of multiple pigmented nevi,
which are colored spots on the skin, or moles.
Almost all individuals with Turner syndrome have short stature. This is partially due to the loss of one copy of the SHOX
gene on the X-chromosome. This particular gene is important for long bone growth. The loss of SHOX may also
explain some of the skeletal features found in Turner syndrome, such as short fingers and toes, and irregular rotations
of the wrist and elbow joints. Linear growth is attenuated in utero, and statural growth lags during childhood and
adolescence, resulting in adult heights of 143-145 cm (approximately 4 feet 8 inches). Final adult height in Turner
syndrome can be increased by a several inches if growth hormone (GH) treatment is given relatively early in childhood.
Unknown genes on the X-chromosome regulate the development and functions of the ovary. Most individuals with
Turner syndrome experience loss of ovarian function early in childhood, and thus do not enter puberty at the normal
Some teenagers may undergo some breast development and begin menstruating, but cease further development and
menses during the later teen years. A few women with Turner syndrome have apparently normal ovarian function with
regular menses until the mid-20s before ovarian failure occurs. A few spontaneous pregnancies have been reported.
It is standard medical practice to treat girls with Turner syndrome with estrogen to induce breast development and
other features of puberty if Spontaneous puberty does not occur. Girls and women with Turner syndrome should
takeestrogen-progesterone treatment to maintain their secondary sexual development and to protect their bones from
osteoporosis until ~ the usual age of menopause (50 years).
Most women with Turner syndrome do not have ovaries with healthy oocytes capable of fertilization and embryo
formation. Current assisted reproductive technology, however, may allow women to become pregnant with donated
oocytes. However, the risk of maternal complications such as diabetes, high blood pressure and aortic dissection, is
high in women with Turner syndrome.
From 5-10% of children with Turner syndrome are found to have a severe constriction of the major blood vessel coming
out from the heart, a condition known as "coarctation of the aorta." This can be surgically corrected as soon as it is
Other major defects in the heart and its major vessels are reported to a much lesser degree. Approoximately 30% of
individuals with Turner syndrome are reported to have "bicuspid aortic valves," meaning that the major blood vessel
from the heart has only two rather than three components to the valve regulating blood flow. This condition has been
discovered mainly by medical imaging studies on women without symptoms, and may not be clinically obvious. It
requires careful medical monitoring, since bicuspid aortic valves can deteriorate or become infected. Comprehensive
screening and evaluation by a cardiologist with expertise in congenital heart conditions is essential for all patients with
Turner syndrome at the time of diagnosis. The evaulation should include cardiac magnetic resonance as well as
echocardiography and ECG.
Many women with Turner syndrome have high blood pressure, which may be apparent even in childhood. In some
cases this high blood pressure may be due to aortic constriction, or to kidney abnormalities (see Kidney section
below). In a majority of women, however, no specific cause for the high blood pressure has been found.
Kidney malformations affect ~ 1/3 of individuals with Turner. T. While the kidneys usually function normally, there may
be a tendency towards urinary infections.
There is a high incidence of osteoporosis--meaning thin or weak bones--in women with Turner syndrome.
Osteoporosis leads to loss of height, curvature of the spine and increased bone fractures.
The primary cause of osteoporosis in individuals with Turners appears to be inadequate circulating estrogen in the
body. Turner women who have low levels of estrogen due to ovarian failure can take estrogen treatments, which will
help prevent osteoporosis. It is possible that other factors contribute to the severity of osteoporosis in Turner
syndrome. For example, there may be defects in bone structure or strength related to the loss of unknown
X-chromosome genes. This is an area of major medical significance, which demands further study to help prevent
osteoporosis and fractures in women with Turner syndrome.
Type II diabetes, also known as adult onset diabetes , has a high occurrence rate in individuals with Turner syndrome.
Individuals with Turner syndrome have twice the risk of the general population for developing this disease. The reason
for the high risk of diabetes amongst individuals with Turner syndrome is unknown but there appears to be insufficient
insulin release in response to glucose.
Diabetes type II can be controlled through careful monitoring of blood-sugar levels, diet, exercise, regular doctor visits
and sometimes medication.
Approximately 1/3 of individuals with Turner syndrome have a thyroid disorder, usually hypothyroidism. Symptoms of
this condition include decreased energy, dry skin, cold-intolerance and poor growth.
In most cases, it is caused by an immune system attack on the thyroid gland (also known as Hashimoto's thyroiditis).
Although it is not known why thyroid disorders occur with a high frequency in Turner syndrome, the condition is easily
treated with thyroid hormone supplements.
Cognitive Function/Educational Issues
In general, individuals with Turner syndrome have normal intelligence. However, some girls and women with Turner
syndrome may have difficulty with specific visual-spatial coordination tasks (e.g. mentally rotating objects in space) and
learning math (geometry, arithmetic). This very specific learning problem has been termed the "Turner neurocognitive
phenotype" and appears due to loss of X-chromosome genes important for selected aspects of nervous system
development. The verbal skills of individuals with Turner syndrome are usually normal or superior.
Genetic Features of Turner Syndrome
Turner syndrome is a disorder caused by the loss of genetic material from one of the sex chromosomes.
Humans normally have a total of 46 chromosomes (which are tiny, DNA-containing elements) that are present in every
cell of the body. DNA encodes genes, which specify all the proteins that make up the body and control its functions.
In humans, there are 23 matched pairs of chromosomes in every cell. Each cell contains 22 pairs of chromosomes
called autosomes that are the same in males and females. The remaining pair of chromosomes, the X- and
Y-chromosomes, are not shaped similarly, and thus are not matched in the same way as the autosomes.
The X- and Y-chromosomes are called sex chromosomes. They are responsible for the difference in development
between males and females. A Y-chromosome contains genes responsible for testis development; and the presence
of a X-chromosome paired with a Y-chromosome will determine male development. On the other hand, two
X-chromosomes are required for normal ovarian development in females.
During the process in which oocytes (eggs) or sperm are formed, one of the sex chromosomes is sometimes "lost".
An embryo receiving only a Y-chromosome can not survive, but an embryo receiving only a X-chromosome may survive
and develop as a female with Turner syndrome.
In order to examine the matching pairs of chromosomes for a person, doctors can perform a blood test and look at the
chromosomes found in the lymphocytes, a particular type of blood cell. This will determine the karyotype of that
The karyotypeof X-monosomy is termed, "45X" meaning that an individual has 44 autosomes and a single
X-chromosome. The usual female karyotype is 46, XX.
A sex chromosome may also be lost during early stages of embryonic development, such that some cells of the
growing body receive a single X chromosome. This condition is called mosaicism, and the clinical features of Turner
syndrome correlate with the relative percentage of 45X cells within the body.
If only a small percentage of cells have been affected, the phenotypes of Turner syndrome may be relatively mild. In
other words, mosaicism may lessen the severity of certain clinical features. An example of the lessened effects due to
mosaicism is if a woman with Turner syndrome experiences regular menstrual cycles until her late 20's rather than not
having any menstrual cycle at all (see Puberty/Reproduction section, Clinical Features).
The genetic diagnosis in such cases may require the examination of many, many blood cells, and/or the examination
of other cell types such as skin cells. The genotype is usually specified as 45X (10)/46XX (90) to indicate for example,
that 10% of cells examined were found to have X-monosomy.
A third cause of Turner syndrome involves X-chromosome defects rather than complete loss. For example, one
X-chromosome may be fragmented, have portions deleted or other structural problems such as ring formation
preventing the normal expression of X-chromosome genes.
The clinical consequences of having one normal and one structurally defective X-chromosome vary widely. A small
deletion may result in a single feature such as ovarian failure or short stature and no other effects. Larger deletions or
deletions affecting critical areas regulating the whole chromosome may result in a full spectrum of Turner syndrome
problems. Abnormal X chromosomes are frequently lost during cell division during embryogenesis, resulting in an
individual that is mosaic for 46,X,abnX and 45,X cell lines.
Moreover, the presence of small ring X-chromosome causes severe consequences, because in addition to absence of
some important genes, there may be deleterious expression of X-chromosome genes that are normally silenced, or
inactivated in the second X-chromosome. The diagnosis of abnormal X-chromosomes may require specialized,
molecular cytogenetic studies to identify small deletions or inversions of X-chromosome material.
Is Turner Syndrome 'Hereditary'?
While Turner syndrome is genetic in that it involves the loss or abnormal expression of X-chromosome genes, it is not
usually hereditary in the conventional sense. That is, it does not typically "run in families." The one exception to this
observation are families with a X-chromosome deletion which is stable enough to be passed down through the
generations and which also allows fertility.
Turner syndrome affects all races, nationalities and regions of the world equally, and parents who have produced many
unaffected children may still have a child with Turner syndrome. There are no known toxins or environmental hazards
that increase the chances of Turner syndrome.
A woman with Turner syndrome has a low probability of being fertile, since the ovaries are negatively impacted in this
disorder. However, if she does become pregnant and passes on her normal X-chromosome to her offspring, no
continuation of the syndrome is expected.
SOURCE National Institues of Health Eunice Kennedy Shriver National Institute of Child Health and Human
Development, Online Publication October 2009