Turner syndrome

Turner Syndrome is a monosomic condition in which only one X chromosome is present (XO). This presents itself as 45,X in terms of karyotype.

Karyotype

Instead of having a set of 44 autosomes + 1 pair of sex chromosomes (either XX or XY) - the normal human karyotype, the person has only 44 autosomes + 1 X chromosomes. A person with Turner syndrome will have no barr bodies due to them only have 1 X chromosome.

Cause

Turner syndrome occurs as a result of nondisjunction, which is when chromosomes do not separate successfully during meiosis. It happens in about 1 in 5000 female births.

Phenotype

The affected person is phenotypically female but does not undergo sexual maturation. This leads to poor breast development (with the nipples spread a distance apart)  and the absence of menstruation. Other phenotypes present include being short in stature, having a low hairline,a short and webbed neck and having small finger nails. These characteristics are present due to an obstruction of the lymphatic system during foetal development. Also, the constriction of the aorta is another phenotype of this syndrome. However, mental abilities are typically within the normal range. Furthermore different karyotypes found in patients with Turner Syndrome will manifest themselves as different phenotypes of the disease. However more than 99 percent of (turner syndrome) foetuses undergo spontaneous abortion. this indicates that the condition has profound deleterious effects on development.