Although this mosaic cell population in females may have similar effects as the defect in males, an additional disease mechanism might be cellular interference, as is the proposed disease mechanism in PCDH19-related epilepsy.23–26 In females, PCDH19 mutations cause variable degrees of epilepsy, behavioural problems and intellectual deficits, while male carriers are unaffected. Here, PCDH19 is linked to epilepsy.