Usually, a female has two copies of the X chromosome (XX) while males typically have an X and Y chromosome (XY). The last pair of chromosomes are known as the “sex chromosome” and typically determines gender. Any variation in the number of sex chromosomes (extra or missing X or Y chromosomes) causes a sex chromosome condition.
X and Y chromosome variations affect about 1 in 500 people. Some sex chromosome conditions never show any signs throughout a lifetime. The life expectancy for people with sex chromosome conditions is usually the same as the rest of the population though there is greater risk of miscarriage for some sex chromosome conditions, such as Turner syndrome (1). Individuals with a sex chromosome condition may have some symptoms that include developmental delays, treatable psychological issues, and some physical or growth differences. For example, a woman with three copies of the X chromosome may be taller than her peers but may not have any other developmental or physical signs of an extra chromosome. Most individuals with sex chromosome conditions do not have intellectual disabilities. (2)
Turner Syndrome (TS) occurs when there is only one copy of the X chromosome and affects about 1 in 2,500 newborn girls and affects each individual differently. Some have features noticed at birth while others are not apparent until adolescence or adulthood. Although females with TS are usually infertile and shorter than average, most have normal sexual function and can grow and develop typically with hormone therapy. Other health conditions may include treatable heart defects (30-50%), minor physical features, skeletal differences, or kidney issues. Women with TS usually have typical intelligence and have an increased chance for learning disabilities that can be treated with support and early education. Most adults with TS function well and live independently. (3) (4)
Klinefelter syndrome or 47, XXY, is found in about 1 one in 600 males. Some individuals with Klinefelter syndrome have different degrees of learning difficulties and developmental delays. Most men with Klinefelter syndrome are taller than average and are infertile. Many men who have Klinefelter syndrome do not know they have it until undergoing an evaluation for infertility. Recent advances in assisted reproduction technology have allowed for the possibility of those with Klinefelter syndrome to father biological children. (2)
For more information about prenatal testing and prenatally diagnosed conditions, click below:
Understanding Chromosome Conditions
Trisomy Conditions (Down syndrome, Trisomy 18, and Trisomy 13)
Sex Chromosome Conditions (Turner syndrome, Klinefelter syndrome)
Neural Tube Defects (Spina Bifida)
Microdeletions (Angelman/Prader-Willi, 22q, Wolf-Hirschhorn, Cri-du-Chat, Jacobsen, and Williams syndrome)
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