Sex chromosome anomalies are a group of genetic disorders caused by a gain, loss, or abnormality of the X or Y chromosome (sex chromosomes). Normally, a female has two X chromosomes for her sex chromosome pair (XX), while a male has an X chromosome and a Y chromosome for his sex chromosome pair (XY). Female sex chromosome anomalies typically affect the number of X chromosomes a female has, while male sex chromosome anomalies can affect the X chromosome, the Y chromosome, or both.
Common female sex chromosome anomaly disorders include Turner syndrome, where only one copy of the X chromosome is present (X0), and multiple X chromosome syndromes, such as triple X syndrome (XXX), XXXX syndrome or XXXXX syndrome. Common male sex chromosome anomaly disorders include Klinefelter syndrome, where an extra X chromosome is present in a male (XXY), and XYY syndrome. Features of sex chromosome anomaly syndromes vary and depend on the specific syndrome. In general, sex chromosome anomaly syndromes have features that are less severe than other chromosome anomaly syndromes, such as Down syndrome, which is due to three copies of chromosome 21, or trisomy 18, which is due to three copies of chromosome 18.
In most cases, sex chromosome anomalies are random (sporadic) and not inherited from an affected parent. All sex chromosome anomaly syndromes can be diagnosed with a chromosome analysis, called a karyotype. Karyotypes show the number, size, and shape of the chromosomes in the individual’s cells. A karyotype can be created by using a blood sample from a child or can be created before a baby is born (prenatally) by using a procedure to collect a sample of the baby’s cells, such as chorionic villus sampling (CVS) or amniocentesis. You can learn more about each sex chromosome anomaly syndrome in their own separate disease description. Support groups are available for more information and support.