ARX and early-infantile DEE: Mutations in the ARX gene lead to various disorders such as X‐linked infantile spasm (ISSX), X‐linked myoclonic seizures, hydranencephaly with abnormal genitalia, X‐linked lissencephaly with abnormal genitalia (XLAG), spasticity and intellectual disability, Partington syndrome, nonsyndromic X‐linked intellectual disability, Ohtahara syndrome, idiopathic infantile epileptic dyskinetic encephalopathy, and Proud syndrome (Bienvenu et al., 2002; de Souza et al., 2006; Grønskov et al., 2004; Kato et al., 2004, 2007; Kitamura et al., 2002).