Our finding is consistent with loss-of-function mutations in ARX causing XLAG in hemizygous males and extends the findings of ID and seizures in heterozygous females.
Furthermore, our data demonstrate that some of the neurobehavioral features found in patients with ARX mutations may not be due to on-going seizures, as is often postulated, given that epilepsy was eliminated as a confounding variable in these behavior analyses.
Given the overlapping and heterogeneous clinical features of CDKL5- and ARX-related epilepsies and SMEI/DS, we postulated that CDKL5 mutations in females and ARX mutations gene in males may be associated with early onset seizures forms of SMEI/DS.
ARX is a crucial gene for the development of interneurons in the fetal brain, and a polyalanine expansion mutation of ARX causes mental retardation and seizures, including those of West syndrome, in males.