Mutations in the PCDH19 gene, located on chromosome X and encoding the protocadherin 19, were originally identified in Epilepsy and mental retardation limited to females (or Epilepsy, Female-restricted, with Mental Retardation, EFMR; MIM# 300088) (Dibbens, et al., 2008). Here, PCDH19 is linked to epilepsy.