The causes and consequences of random and non-random X chromosome inactivation in humans


Corresponding author: Carolyn J Brown, Department of Medical Genetics, University of British Columbia, 6174 University Boulevard, Vancouver, BC V6T 1Z3, Canada. Fax: +604 822 5348; e-mail:


X chromosome (X) inactivation is a remarkable biological process including the choice and cis-limited inactivation of one X, as well as the stable maintenance of this silencing by epigenetic chromatin alterations. The process results in females generally being mosaic for two populations of cells – one with each parental X active. In this review, we discuss recent advances in our understanding of how inactivation works, as well as the causes and clinical implications of deviations from random inactivation.