Overview of sex chromosome anomalies

[Oralee]

Sex chromosome anomalies may involve aneuploidy, partial deletions or duplications of sex chromosomes, or mosaicism.
(See also Overview of Chromosomal Anomalies.)
Sex chromosome anomalies are common and cause syndromes that are associated with a range of congenital and developmental anomalies. The majority are not suspected prenatally but may be incidentally discovered if karyotyping is done for other reasons, such as advanced maternal age. The anomalies are often hard to recognize at birth and may not be diagnosed until puberty.
The effects of X chromosome anomalies are not as severe as those from analogous autosomal anomalies. Females with 3 X chromosomes often appear normal physically and mentally and are fertile. In contrast, all known autosomal trisomies have devastating effects. Similarly, whereas the absence of 1 X chromosome (monosomy leads to a specific syndrome (Turner syndrome), the absence of an autosome is invariably lethal.