Turner Syndrome

Turner syndrome is named for Henry Turner who, in 1938, was one of the first doctors to report on the disorder in the medical literature. Turner syndrome is one of the most common chromosomal disorders and likely the most common genetic disorder of females.

Turner syndrome is a rare chromosomal disorder that affects females. The disorder is characterized by partial or complete loss (monosomy) of one of the second sex chromosomes. Usually, a female has two X chromosomes. However, in females with Turner’s syndrome, one of these chromosomes is missing or abnormal. Turner syndrome is highly variable and can differ dramatically from one person to another. Affected females can potentially develop a wide variety of symptoms, affecting many different organ systems. Common symptoms include short stature and premature ovarian failure, which can result in the failure to attain puberty. Most women with Turner syndrome are infertile. A variety of additional symptoms can occur including abnormalities of the eyes and ears, skeletal malformations, heart anomalies, and kidney abnormalities. Intelligence is usually normal, but affected individuals may experience certain learning disabilities. Turner syndrome may be diagnosed before birth or shortly after birth or during early childhood. However, in some cases, the disorder may not be diagnosed until well into adulthood, often as an incidental finding. Most cases do not run in families and appear to occur randomly for no apparent reason (sporadically).

Symptoms

The most significant features of Turner’s syndrome include:

• short stature – average adult height is 143 cm (4’ 8”)
• infertility – due to underdeveloped ovaries
• congenital heart defects – in about 50 per cent of affected women
• spatial awareness issues – problems with tasks such as maths
• absence of menstruation (amenorrhoea)
• hearing problems.

Less significant features may include:

• sunken, wide chest with broadly spaced nipples
• extra skin (‘webbing’) on the neck
• puffy hands and feet
• inability to straighten the elbow joints
• pigmented moles
• soft upturned nails
• low hairline.

Causes

When a baby is conceived, a normal egg cell and normal sperm cell start with 46 chromosomes. The egg and sperm cells then divide in half. The egg and sperm cells then have 23 chromosomes each. When a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, the baby will then have a complete set of 46 chromosomes, or 23 pairs. Half are from the father and half are from the mother. The 23^rd pair is called the sex chromosomes. In females, the 23^rd pair is two X chromosomes. In males, the 23rd pair is one X and one Y chromosome.

There are 2 types of Turner syndrome: monosomy X TS and mosaic TS. About half of all girls with Turner syndrome have a monosomy disorder. Monosomy means that a person is missing one chromosome in the pair. Instead of 46 chromosomes, the person has only 45 chromosomes. This means a girl with TS has only one X chromosome in her 23^rd pair. Sometimes an error occurs when an egg or sperm cell is forming. This causes it to have a missing sex chromosome. But it is often an error that happened by chance when the father's sperm cell was forming. The missing sex chromosome error can occur in either the mother's egg cell or the father's sperm cell.

Girls with mosaic TS have chromosome changes in only some cells, but not all cells. A small number of cases have the normal number of 46 chromosomes, but with part of the X chromosome missing. When only part of an X chromosome is missing (deletion), a girl with the syndrome will often have milder signs of TS. The features of TS depend on which part of the X chromosome is missing.