Correlation between clinical severity in patients with Rett syndrome with a p.R168X or p.T158M <i>MECP2</i> mutation, and the direction and degree of skewing of X-chromosome inactivation

XCI may vary in neurological and haematological tissues. However, these data are the first to show a relationship between the degree and direction of XCI in leucocytes and clinical severity in RTT, although the clinical utility of this in giving a prognosis for individual patients is unclear.