Recently, PCDH19 mutations were shown to cause epilepsy and mental retardation limited to females (EFMR), a familial disorder associating childhood-onset epilepsy and a variable degree of cognitive impairment with an unusual mode of inheritance: this X-linked disorder is found in females with heterozygous mutations but not in males with hemizygous mutations [6]. The gene discussed is PCDH19; the disease is epilepsy.