L. Allou and colleagues conduct next-generation sequencing to evaluate for mutations in known or new candidate genes in patients with variant forms of Rett or Rett-like phenotypes of unknown molecular aetiology. They identified a missense (p.Ser240Thr) in CDKL5 in a patient who appeared to be seizure free. They also identified a premature stop codon (p.Arg926*) in IQSEC2 in a patient with a Rett-like phenotype. Their exome sequencing exome sequencing enabled them to characterize a heterozygous de novo missense (p.Val408Ala) in KCNA2 encoding the potassium channel Kv 1.2 in a girl with infantile-onset seizures variant of RTT.