Curr Opin Genet Dev.
In the present review, we will limit our discussion of escape from X inactivation to female somatic cells. This is consistent with our recent observations that mouse escape genes contain fewer AT-rich motifs than genes subject to X inactivation Nguyen et al.
Genes and brain sex differences. The single active X in human cells: evolutionary tinkering personified.
Escape genes appear to be protected from the repressive chromatin modifications associated with X inactivation. This could result in disease phenotypes due list of sex chromosome disorders in Grafton increase expression of genes that are normally repressed or in expression of X-linked mutations in women carriers.
Escape from X inactivation. There is also evidence that AT-rich motifs are depleted at escape genes Fig. There is no actual cure for this syndrome but treatments can be done to alleviate some of its symptoms, e. X inactivation and the complexities of silencing a sex chromosome.
Clinical indications that should raise suspicions of a sex chromosome abnormality are: delay in onset of puberty; primary or secondary amenorrhea; infertility; ambiguous genitalia.
Research suggests, however, that in a few births per thousand some individuals will be born with a single sex chromosome 45X or 45Y sex monosomies and some with three or more sex chromosomes 47XXX, 47XYY or 47XXY, etc. The Xist RNA gene evolved in eutherians by pseudogenization of a protein-coding gene.
X inactivation and escape could not only enhance phenotypic differences between males and females, but could also enhance variability within the female sex due to mosaicism for cells with the Xm or Xp inactivated and to variable escape from X inactivation Fig. Affected individuals are usually taller than average and have slender builds.