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Turner syndrome

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Turner syndrome

Definition

Turner syndrome refers to a genetic condition whereby a female does not posses the normal pair of two X chromosomes. The syndrome is called after Dr. Henry Turner an endocrinologist in Oklahoma who described the disease in 1938. It is a chromosomal disorder which only affects females. The condition is also called Gonadal dysgenesis. The condition is characterized by the absence of all or part of the second sex chromosome in all or some of the cells. Estimates show that almost one in every between 2500 and 3000 acquire the condition at birth. People who do not have Turner syndrome possess 46 chromosomes with two sex chromosomes.

Normal females have a pair of X chromosomes. People who have Turner Syndrome either have one of the sex chromosome missing or have other abnormalities. Chromosomes are DNA (deoxyribonucleic acid) strands, which are present in all the cells of the human anatomy. Chromosomes contain a set of instructions that determine the human physical and behavioral characteristics. The two types of Turner’s syndrome are Classical Turner Syndrome and Mossaic Turner Syndrome. Classic Turner Syndrome is a condition when an X chromosome is completely absent (Gravholt, 2004). Mosaic Turner syndrome refers to when the abnormalities or disorder occur in the X chromosome of particular cells in the body.

Etiology

Etiology refers to the study of all factors or elements that can be involved in the development or progress of a disease. This includes patient susceptibility, nature of the agent of the disease and the technique in which the body of the patient is invaded by the agent. Etiology is therefore the science and study of the origins and causes of the disease. The origin or cause of the disorder or disease is determined through medical diagnosis. Etiology of Turner Syndrome involves the abnormality or loss of the X chromosome. However, having a child with Turner syndrome does not pose the risk of subsequent children also having the disorder.

The disorder affects females only. Genetic alterations that occur in Turner Syndrome (TS) are monosomy, Y chromosome material and Mosaic Turner syndrome. In monosomy, one X chromosome is completely absent. This can be the result of errors either in the mother’s ovum or the father’s sperm. Each cell in the body of the offspring has one absent X chromosome. In Y chromosome material, few patients with TS have particular cells that possess one X chromosome and the rest of the cells having one X chromosome copy and several Y chromosome material. Turner Mosaicism (Mosaic Turner Syndrome) can be the result of an error that occurred in the early stages of fetal development during cell division. The process can produce cells containing a pair of X chromosome copies and some to have just one. In some instances, some cells may posses both X chromosome copies and some with one copy that is altered.

Epidemiology

The epidemiology of Turner syndrome is widely unknown. However, studies of incidence and prevalence of TS are performed with statistics showing that the condition occurs in 50 per 100, 000 live born females. Post natal prevalence of TS is much lower than pre natal prevalence. Turner syndrome karyotypes following chorion villus sampling are evidence of the prenatal prevalence. Diagnosis of TS during prenatal care is not correct at all times especially the mosaic cases. Prevalence of TS is based on several cytogenetic studies.

Cytogenetic surveys show that TS diagnosis is less frequent in comparison with the original surveys (Gravholt, et. al., 2006). There is also a delay in the diagnosis of the disease as most children are diagnosed during adolescence. Morbidity is increased in TS. The risk of other illnesses such as thyroiditis, hypothyreosis, type 1 and 2 diabetes, vascular brain disease, ischemic heart disease, hypertension, arteriosclerosis, liver cirrhosis, osteoporosis, fractures and congenital malfunctions of the heart are susceptible to occur in most TS patients. Mortality is increased in TS. In a cohort study in Britain, the relative risk of death was 4.2 because of diseases in the digestive, nervous, genitourinary and respiratory systems.

The graph shows the number of females diagnosed with Turner Syndrome in Denmark between 1970 and 2001.

Pathophysiology

Pathophysiology refers to the study of physical and biologic manifestations of ailments as they connect with physiologic disturbances and underlying abnormalities. Pathophysiology therefore sets to explain processes in the body which bring about the signs and symptoms of an illness. Pathophysiology is the physiology of abnormal conditions or disordered functions. Pathophysiology deals with the functional changes which accompany a specific disease or syndrome. A pathophysiologic alteration or disorder is the change in function that is distinguished from a structural defect. Pathophysiology stresses on quantifiable measurements while studying the abnormal syndrome or disease.

Pathophysiology of Turner syndrome involves the homologous regions of sex chromosomes act like autosomes as they go through the process of homologous recombination and pairing. They also possess genes that escape from X-inactivation. The genes are presumably needed in dual dosage in females and males. The pseudo-autosomal region 1 that is situated in the Xp terminus has close to 20 annotated genes and a number of predicted genes. The pseudo-autosomal region 2 located at the Xq terminus contains a slighter set of homologous genes. Haplo-insufficiency for the PAR1 genes is associated with Turner’s syndrome.

Pseudo-autosomal regions of X and Y chromosomes.

Short stature caused by impaired skeletal development and impaired long bone growth is associated with Haplo-insufficiency of a particular sex chromosome gene called SHOX. SHOX is located in the pseudo-autosomal region. The role of the gene is to encode a transcription factor that is expressed in the development of cartilage and bones. Other pseudo-autosomal regions can have Haplo-insufficiency. The insufficiency can lead to congenital cardiovascular defects. The heart is an important organ in the human body. However, the cardiovascular complications produce high levels of mortality in Turner’s syndrome.

People with Turner’s syndrome also suffer from premature ovarian failure. Causes of the condition are unclear. However, genes in the long and short arms of X chromosomes are linked to the condition. The long arm of the chromosome Xq contains the X inactivation Center

(XIC). The deletion of the Xq distal towards the XIC is more related to premature failure of the ovary as compared to features in Turner Syndrome. Normally, ovaries form in 45, X feminine fetuses. On the other hand, most exhibit accelerated oocyte loss and degeneration of ovaries into fibrous streaks. Genes on Xp have Haplo-insufficiency that leads to individual neurocognitive traits. These include superior verbal versus visual-spatial capabilities and difficulties in the detection of facial expressions.

Signs and symptoms

Signs are the conditions that other people such as doctors detect in a patient. Symptoms refer to what the patient reports and feels. Signs and symptoms in Turner syndrome (TS) may vary considerably and manifest before and after birth. Unborn females who have Turner syndrome may have lymphedema. Lymphedema is a condition where fluid is not effectively transported around the body organs causing excessive fluid leaks to the tissues that surround the organs (Sperling, 2008). Consequently, the unborn child’s body swells. Most babies born with TS are born with swollen feet and hands. Other symptoms for the unborn include; relatively lower weight, cystic hygroma which is the swelling of the neck and thickness in the neck tissue.

Girls with Turner Syndrome have slow growth rates and are generally shorter than average (Boman, 2008). Girls also have non functioning ovaries and therefore cannot have menstruation or develop breasts. However this can be altered by hormone treatment. Earlier in their childhood, the girls can have middle ear infections which can lead to hearing loss when recurrent. Other symptoms include; a broad chest with widely spaced nipples, webbed neck and indistinct or low hairline, high blood pressure, minor eye problems, spine deformities (scoliosis), underactive thyroid, high risk of diabetes, osteoporosis and a heart murmur.

Body structure of a girl with Turners syndrome

Interventions (Testing and Treatment)

Diagnosis of Turner syndrome can be done at an earlier stage in the life of the female. Diagnosis is done before birth through chromosomal analysis in pre natal testing or after the birth of the baby. Doctors perform physical examinations while searching for the signs of poor development. Tests such as ultrasound for reproductive and kidney organs, chest MRIs, Karyotyping, echocardiogram and pelvic exams help determine the condition. Blood hormone levels such as follicle stimulating hormone (FSH) and luteinizing hormone are also tested to detect Turner Syndrome.

In childhood and adolescence girls are placed under the care of pediatric endocrinologists. These specialists deal with hormonal and metabolic conditions of children. Children are given growth hormonal injections to help them grow. At puberty, around 12 years the child undergoes estrogen replacement therapy to start breast development. Progesterone and estrogen are given later to start menstruation and prevention of osteoporosis by estrogen. Babies with heart murmurs need surgery to correct the defect. Ear infections are likely in TS patients and they are regularly evaluated by an ENT specialist. Routine blood pressure checks are necessary for regulation. Most women with the condition are infertile but they can have donor embryos for pregnancy (Hamilton, et. al., 2008). There are hospitals that offer treatment specifically for TS patients. Appropriate treatment can help a woman lead a healthy and normal life.

Extra information

Since the description of Turner syndrome in the year 1938, a wealth of information has increased to the contemporary understanding of the syndrome and continuous broadening of information and research. In recent times, care and treatment of the condition has involved numerous specialties like embryology, genetics, obstetrics and gynecology, ophthalmology, cardiology, endocrinology and gastroenterology. Patients with the condition require comprehensive care from a multidisciplinary and holistic team. Knowledge and awareness on TS is relatively limited among the masses. People are either not aware of the condition or have established myths and misconceptions about Turner syndrome.

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