The X Chromosome: Sex-specific Effects in Infectious Disease

While the X Chromosome Inactivation process in humans is not yet fully understood, studies of human aneuploidy indicate that in a diploid human cell there is always just one active X chromosome in either sex. In Turner syndrome, individuals have only one sex chromosome (one X chromosome, X0) which is kept active, while in males with Klinefelter syndrome (XXY) one X chromosome is silenced. This suggests that the human XCI mechanisms protect one X chromosome while inactivating all others.