Twenty-eight patients with early onset SMEI/DS before 6 months negative for SCN1A mutational screening were selected and screened for mutations in the ARX gene in males (n = 14) or the CDKL5 gene in females (n = 14).
No mutations in either gene were found except one intronic variation of uncertain pathogenicity in the CDKL5 gene. All patients started seizures at mean age of 3.48 months. Thirteen patients had familial history of epilepsy or febrile seizures. Patients evolved toward refractory epilepsy with generalized tonic clonic seizures (18/28) and myoclonia (23/28) and severe neurological impairment with autistic features (13/28), ataxia (14/28) and spasticity (5/28). No patient ever exhibited infantile spasms, dystonia, or Rett-like features.
Our results illustrate that mutation screening of ARX and CDKL5 is not effective in patients selected on the basis of clinical signs associated to early onset SMEI/DS. In addition, they might reflect that other phenotypic features associated with CDKL5 mutations (Rett-like features, infantile spasm) or ARX mutations (dystonia, spasticity) are more distinctive.