Turner syndrome is a disorder caused by a partially or completely missing X chromosome. This condition affects only females.
Most people have 46 chromosomes in each cell—23 from their mother and 23 from their father. The 23rd pair of chromosomes are called the sex chromosomes—X and Y—because they determine whether a person is male or female. Females have two X chromosomes (XX) in most of their cells, and males have one X chromosome and one Y chromosome (XY) in most of their cells. A female with all of her chromosomes is referred to as 46,XX. A male is 46,XY.
Turner syndrome most often occurs when a female has one normal X chromosome, but the other X chromosome is missing (45,X). Other forms of Turner syndrome result when one of the two chromosomes is partially missing or altered in some way.1