Turner syndrome: The most common sex chromosome disorder in females, characterized by short stature, webbed neck, broad shield-like chest, wide-spaced nipples, increased carrying angle at the elbow (cubitus valgus), short fourth finger, and malformations of the heart and aorta. The intelligence of those with Turner syndrome is usually within the normal range. Girls with Turner syndrome at the time of puberty do not experience the development of secondary sex characteristics such as breast enlargement. As women, they are infertile due to ovarian failure. The ovaries typically contain no follicles and look like streaks of fibrous tissue. The diagnosis of Turner syndrome is confirmed with chromosome analysis (karyotype). Turner syndrome is due to the presence of only one normal X chromosome and no other normal sex chromosome. A second sex chromosome may be present, but it is not structurally and functionally normal. However, the most frequent karyotype in Turner syndrome is 45, X, which is sometimes referred to as XO. The overwhelming majority of pregnancies with Turner syndrome conceptions result in miscarriages.