Health - Conditions
By: - at July 13, 2013

What is Turner Syndrome and Why Does it Affect Only Females?

Turner syndrome occurs only in females and is caused by structural defects or incomplete X-chromosomes. When one of the two X-chromosomes present in a female embryo is missing, defective, or has deleted portions then Turner syndrome may develop.

ChromosomeChromosomal disorders can occur when there is change in the number or structural composition of chromosomes, resulting in abnormalities. Turner syndrome is a condition that only affects females and does not occur in males. It is estimated that about 60,000 females in the US are affected by Turner syndrome, with close to 800 new cases of the disorder being diagnosed each year. This condition is witnessed in 1 out of every 2000 to 2500 newborn babies. Turner syndrome is mostly detected at birth but at other times, it can remain undiagnosed until the girl reaches puberty.  Typically a failure to grow breasts can be indicative of Turner syndrome and the condition is most accurately diagnosed during puberty when patients do not develop in a typical fashion. 

What is Turner Syndrome?
Turner syndrome is a chromosomal condition caused by incomplete X-chromosomes or the missing of one of the two X chromosomes. A person who suffers from this condition will develop as a female. Chromosomes are body structures, which hold genes, and there are 23 pairs of these chromosomes in a normal person. Due to certain disorders the number may differ from a normal person which can cause some genetic abnormalities.

Chromosomes are found in the nucleus of every cell in the body. These chromosomes are passed from the parents to a child where the mother donates 23 chromosomes, called the maternal chromosomes which are located in the egg. The father also passes another 23 chromosomes, known as the paternal chromosomes, and these are found in the sperm.

Sperm and egg

In these chromosomes, there are genes, which are sets of instructions that tell the body how it should develop and function. These genes also determine medical and physical characteristics like blood type, hair color, susceptibility to diseases, growth of sexual characters, and overall bodily development. Among the 23 pairs of chromosomes the first 22 pairs are called autosomes, and the final pair (23rd) is regarded as the sex chromosomes because they determine sexual assignment.

Usually females have sex chromosomes referred to as XX chromosomes, and a male has one X and one Y chromosome which are referred to as XY chromosomes. When a female suffers from Turner syndrome, meaning that there is one missing or incomplete X- chromosome, that individual develops problems with their sexual development. Such a person has a shorter height and develops abnormalities in sex characters. The X-chromosomes or sex chromosomes give instructions on how a person should develop, that is, male or female. They also help in the overall development and growth of the body.

How Does Turner Syndrome Occur?
When one normal X-chromosome is found in cells of a female and the other X-chromosome is missing or has been structurally altered, this may lead to Turner syndrome. This change in the sex chromosomes happens before an egg fuses with a sperm during the process of fertilization. However, the abnormality in the chromosomes is not passed from the parent to a child. It occurs somewhere just before the formation of an embryo.

Diagram of sperm and egg

Due to the missing genetic material, a female with this condition suffers from growth and development problem before and after birth. This leads to a shorter stature, malfunction of ovaries as well as other features associated with Turner syndrome. The abnormality in sex chromosomes in females, which results to Turner syndrome may be caused by an error in cell division in a process known as nondisjunction. The results of nondisjunction are an abnormal number of X-chromosomes.

A reproductive cell could by chance, lose one copy of the sex or the XX chromosomes resulting in only one X-chromosome for a female. In the case of a nondisjunction situation, two sex chromosomes may not divide or separate during the formation of an egg. That abnormal egg fuses with a normal sperm and forms an embryo, which could have one missing X-chromosome.

Human embryo

When an embryo is formed that way, it grows and its cells begin to divide. Every cell the fetus grows with a missing X-chromosome. In other cases, Turner syndrome can occur due to chromosomal changes in some and not all of the cells which is referred to as mosaicism. It is estimated that about half of the people who suffer from Turner syndrome have each cell in the body with only one copy of the X-chromosome, rather than the usual two X or sex chromosomes. However, in mosaicism, only some and not the entire number of cells in body have a change in sex chromosomes. Some of the cells in body have the usual sex chromosomes, which could be the XX or the XY and the other cells have only one copy of the X-chromosome.

What Causes Turner Syndrome
Loss of genetic material within one of the two sex chromosomes is believed to be the cause of Turner syndrome. This change in sex chromosomes can happen through processes such as monosomy, mosaicism or genetic defects. X-chromosome monosomy occurs during fertilization. This means that an embryo, which receives one X-chromosome, will develop into a female who suffers from Turner syndrome. However, an embryo, which receives one Y chromosome and no X-chromosome, does not survive and therefore a fetus does not continue to grow.

The X-chromosome mosaicism is another theory, which tries to explain how Turner syndrome may occur. In mosaicism, a sex chromosome is lost in the early phases of the development of an embryo. What happens is that only some cells of the growing embryo have one X-chromosome, while the other cells have normal two X-chromosomes. If only a few cells have these abnormalities, then the Turner syndrome symptoms in that particular patient are mild and less severe.

Human chromosome vectorThe other theory, which explains the cause of Turner syndrome, is a X-chromosome defect in which there is a deformity on the chromosome but not a complete loss. One of the two X-chromosomes may have some portion deleted, fragmented, or some other structurally related changes like ring formation. When these defects occur in one of the sex chromosomes, they prevent the normal expression of genes within the X-chromosomes. This is something that results in problems with defining sex characteristics and growth. The severity of the Turner syndrome arising from X-chromosome defect can vary widely depending on how and when the deformations occurred. If large portions of one X-chromosome are deleted or fragmented, this can result in various symptoms such as failure of the ovarian function and problem with height development. Small defects can result in a single symptom like a short stature and no other sexual reproductive problems.

It is not uncommon for abnormal X-chromosomes to be lost during the process of cell division when the eggs and sperms are fusing to form an embryo. This process is known as embryogenesis. If the defect involves a ring structural formation in the X-chromosome, the effects could be much worse. The reason is because, such a ringed X-chromosome leads to absence of essential genes as well as deleterious expression of genes in X-chromosomes, which may remain inactive or silent in the second X-chromosome.

Thus, if the second X-chromosome is also affected, it means that the Turner syndrome symptoms become more severe. In a nutshell, X-chromosome monosomy, mosaicism, and defects are three possible causes of Turner syndrome. They may cause varying symptoms in a female depending on which part of the chromosome and genes are affected.

Why Do Girls and Women Suffer From Turner Syndrome and Not Males?
The reason is that if in the process of embryo formation there is loss of X-chromosome from the XY sex chromosomes, which are present in a male fetus, usually the fetus does not survive. However, if one of the two X-chromosomes found in females is deleted, fragmented, or defective, the fetus may survive but go on to develop Turner syndrome.

When an embryo receives only the Y-chromosome and does not have the X-chromosome, the fetus is not able to survive. A female fetus can survive with one X-chromosome instead of the normal two XX chromosomes. The X-chromosome consists of a longer DNA molecule and has many genes that are required for cellular function. In the event that one X-chromosome misses in a normal female fetus, it means that the other one X-chromosome left can provide many of the genes needed for cell functionality. This is why a female foetus with only one X-chromosome will survive but with some abnormalities associated with Turner syndrome.

Dna molecule

On the other hand, Y-chromosome consists of fewer genes required for cell function. A missing X-chromosome is much worse than a missing Y-chromosome. Therefore, if a male fetus that is supposed to have XY chromosomes does not have the X-chromosome; it cannot survive with the only remaining Y-chromosome since this chromosome cannot support the essential cell functions required to sustain life. It will therefore not develop. This is the reason why abnormalities in X-chromosomes only allow a female fetus to grow and the male fetus are not viable and shortly die off. In short, all patients with Turner syndrome are females.

The Symptoms of Turner Syndrome
Symptoms of Turner syndrome will vary depending on the chromosomal changes, the causes, and the genes that are affected. Turner syndrome causes abnormalities in sex development and the overall growth of the body. One of the common symptoms is short stature where a girl grows shorter than normal and lack of breast development.

The failure in puberty development is caused by malfunctioning ovaries. The ovaries are responsible for production of eggs, and sex hormones like estrogen and progesterone.  Below is a human ovary-

If there are problems with the ovaries, it means that the hormones that are responsible for triggering the onset of puberty are not produced. Women with Turner syndrome are not able to conceive because they are infertile. A female with this condition may have a webbed neck in which the areas on top part of shoulders, all the way extending to the sides of neck, develop extra folds of skin.

Moreover, the back of the neck has a low hairline or the hair extends down the neck. Women who suffer from Turner syndrome could have a stocky appearance. Abnormal bone development may be seen around the arms, which turn out considerably at the elbow in Turner patients. Other signs may include drooping eyelids and a lower jaw that is moving back or receding. The ears may also be shaped differently. In addition, they may be unusually set on lower sides of the head.

Self esteemBecause of changes in body functionality caused by the alterations in genes, other symptoms may occur such as swelling of feet and hands, as well as extra fluid in the feet and hands or edema. High blood pressure, defects in heart and kidney, thyroid problems, diabetes, being overweight, and hearing problems may be experienced in girls who suffer from Turner syndrome. As a result of problems in growth and sex character development, girls may experience emotional problems. The short stature appearance of a girl may cause problems with self-esteem such as self-denial.

How is Turner syndrome treated?
Apparently, there is no specific cure for Turner syndrome since the chromosomal changes cannot be corrected once they have occurred. However, the symptoms, which arise from this condition, can be managed. Depending on the cause and the extent of chromosomal changes, different symptoms may occur. Turner syndrome treatment is aimed at managing the symptoms.

Since the condition affects the development of the ovaries that cause problems in the synthesis of hormones responsible for regulation of menstruation and growth of breasts, it means that girls with this disorder do not go through the puberty stage as desired. Oestrogen replacement may be applied to assist a girl to develop the physical changes witnessed in puberty stage such as menstrual periods and breast development.  There has been a decent amount of success with hormone replacement therapy for Turner syndrome patients in addition to success in treating other conditions like menopause.  

Similarly, if the condition causes short stature, growth hormones may be administered to help a girl reach an average adult height. When growth hormone treatment is started early, it could help a girl attain an average height rather than the short height. Turner syndrome causes infertility or inability to have child but this problem can be corrected with the use of artificial fertilization of an egg.

Invitro fertilizationThrough a technique known as in vitro fertilization, some women suffering from Turner syndrome can get pregnant. Usually an egg obtained from a donor is used in creating an embryo, which is then implanted into the womb of a woman with suffering from Turner syndrome. In such a case, the women is able to carry and deliver a baby in the normal way. It is advisable that if a girl suffers from Turner syndrome, she seeks the help of professional therapists who can assist in restoring her lost self-esteem and balance out any emotional issues.

Conclusion
Turner syndrome is a chromosomal condition that only affects females and does not occur in males. No males are born with the condition because in the first place, a male fetus that misses the X-chromosome linked with the condition does not survive. Turner syndrome is genetic but it usually is not passed from the parent to children meaning that it does not run in families. The abnormality occurs somewhere before the egg fuses with the sperm to form the embryo that develops into a fetus. Nonetheless, there is one very rare exception where X-chromosome deletion can occur and remain sufficiently stable to be passed to the next generations. In such a case, the deletion takes place in such a way that it allows fertility to remain and the woman can bear a child.


 

 

 

 

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