Structural Biochemistry/Genetic Diseases/Turner syndrome

Turner Syndrome

Turner syndrome is a genetic disorder that occurs in about 1 in 5,000 births. It is a genetic abnormality that affects the development in only females. Girls born with Turner syndrome show certain physical attributes in which the levels of severity differ greatly between individuals. Most cases of Turner syndrome are not inherited. It is a genetic abnormality in which the female does have the usual pair of two X chromosomes. It is characterized as a chromosomal abnormality when one normal X chromosome is present in a female's cells and the other sex chromosome is missing or structurally altered.

Causes

There are different types of Turner syndrome depending on how much of the X chromosome is missing. Roughly half of the females with classic Turner syndrome have monosomy X, which means each cell in the body has only one copy of the X chromosome than the typical two. In mosaic Turner syndrome, a complete X chromosome is missing in some cells. In other words, one X chromosome may be whole and the other may be partially missing or abnormal. Currently, the exact cause of this condition is unknown, but many scientists conclude that it is a result of a random event during the formation of the reproductive cells. An error in cell division known as nondisjunction is when members of a pair of sister chromatids fail to separate properly from each other. This results in reproductive cells with an abnormal number of chromosomes.

Diagnosis

A diagnosis of Turner syndrome can be made during prenatal tests, at birth, or at any other time. Procedures during prenatal diagnosis include sampling of a small piece of tissue from the placenta or sampling of the amniotic fluid taken from the uterus to detect for any abnormal amniocentesis. Also, a doctor can suspect Turner syndrome based on certain physical features of an individual such as poor physical development and heart or kidney problems. Other tests include blood hormone levels, echocardiogram, MRI of the chest, pelvic exam, or ultrasound of the reproductive organs. Nonetheless, a doctor usually confirms Turner syndrome with a special blood test called a karyotype. This blood test produces an image of the composition of an individual’s chromosomes. From the image, the doctor can identify whether one of the sex chromosomes is missing or partially deleted. The common karyotype that causes Turner syndrome is called “45X” which means an individual has 44 autosomes and a single X chromosome. A karyotype can also reveal mosaic Turner syndrome, which is when an individual’s body is composed of cells with two X chromosomes and some having one 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.

Symptoms

The most common features in young infants are swollen hands and feet, drooping eyelids, spots of skin, and a wide or web-like neck. Other symptoms during childhood may include stunted growth, a flat chest shaped like a shield, incomplete or absent development at puberty, and an early loss of ovarian function and menstrual cycle. Due to the loss of ovarian function, many girls do not start their periods or develop breasts. It is common for girls with Turner syndrome to be sterile, yet still have functioning vagina and womb. There may also be learning disabilities in areas that involves math, though intelligence is typically normal. Also, more severe conditions may be present, including high blood pressure, scoliosis, kidney and heart dysfunctions, thyroid malfunctions, and frequent middle ear infections that can lead to hearing loss.

Possible Treatments

Scientists have developed several treatments to correct some of the problems associated with Turner syndrome. Treatment becomes easier and effective if the disease is diagnosed at an early stage. During childhood and adolescence, growth hormones may help a child grow taller. According to the National Human Genome Research Institute, “Growth hormone injections are beneficial in some individuals with Turner syndrome. Injections often begin in early childhood and may increase final adult height by a few inches”. The growth hormone works by stimulating the growth and reproduction of cells. Unfortunately, growth hormones cannot stimulate bone growth after puberty. Another treatment is estrogen replacement therapy. It is usually started at the time of normal puberty to induce breast development and other sexual characteristics. Girls and women should continue with estrogen-progesterone treatment to maintain their sexual development and to protect their bones from osteoporosis until the age of menopause. Osteoporosis is a condition characterized by the decrease in bone mass and the increase in susceptibility to bone fracture. Moreover, surgeries can correct other medical conditions such as heart defects and kidney problems. Non-medical treatments such as psychological therapy and sex education can also help to reduce the mental stress and impact of complications associated with Turner syndrome. Overall, regular checkups and appropriate care can give most girls and women the potential live relatively healthy and independent lives.