Monosomy X, also known as Turner Syndrome (TS), is a genetic disorder that occurs in girls. It is caused by the complete or partial absence of one of the X chromosomes. Instead of 46 chromosomes, a person with monosomy X has only 45 chromosomes, with only one X chromosome in the 23rd pair. This condition occurs randomly during the formation of reproductive cells (eggs and sperm) in the affected persons parent. The features of TS depend on which part of the X chromosome is missing. Girls with TS are shorter than most girls and don’t go through normal puberty. They may also have other physical characteristics such as a wide neck with folds of skin down the sides of the neck, a low hairline at the back of the neck, and puffy hands and feet at birth. If a healthcare provider thinks that a newborn baby girl may have TS, they will often take a small sample of the baby’s blood to see if one X chromosome is missing.