Turner syndrome is one of the most known and examined chromosomal abnormalities in females. This syndrome is characterized by extremely short stature, the lack of spontaneous development of the secondary sexual characteristics, followed by infertility, broad chest, webbed neck and a series of skeletal, cardiac and renal abnormalities; it was discovered in 1938 by Henry H. Turner. It it also called monsomy X and gonadal dysgenesis.
In order to understand this syndrome, it is important to look over the normal patterns of the chromosomes. After conception, the normally developing fetus has 46 chromosomes from each of the parents, and an X chromosome from the mother and either an X (or Y) chromosome from the father, resulting in 23 pairs of chromosomes in a fetus. If the fetus receives an X chromosome from both of the parents, the child will be a female. On the contrary, if the fetus receives a Y chromosome from the father, the child will be a male. In the case of Turner Syndrome, there is an absence of one of the X chromosomes that the fetus should have received from one of the parents, usually the paternal chromosome. Females with this kind of Turner Syndrome have only one X chromosome and an approximate rate of 50% of the cases of Turner Syndrome have this genotype.
The second case which is most common is the mosaicism, which occurs in 30-40% of the cases. In mosaicism, the division of the cell that replicated the chromosomes fails to replicate the genetic material completely, and some cells contain a different set of chromosomal material. Another type of abnormalities are the partial deletion of one arm of the X chromosome or the duplication of one arm of this type of chromosome, with the loss of the other arm.
The physical manifestations of the patients identified with Turner Syndrome can vary, depending on the chromosomal abnormality present. The most obvious and common physical characteristics include extremely short stature, cubitus valgus (an unusual carrying angle at the elbows), a short forth or fifth metacarpal or metatarsal and the lack of apparition of the secondary sexual characteristics, such as enlarged breast and pubic hair. This lack is caused by the gonadal dysgenesis. During the fetal stage of development and after birth, there is a massive loss of egg cells and thus resulting in a lack of development of the ovaries and infertility.
The patients with this syndrome have a variety of skeletal and facial abnormalities, such as scoliosis, ptosis (which is the name to drooping eyelids), strabismus, low and rotated ears and inner ear defects. Narrowing of the aorta and horseshoe kidney, high blood pressure, obesity, diabetes mellitus, cataracts and arthritis can occur.