The landscape of early infantile epileptic encephalopathy in a consanguineous population

Purpose: Epileptic encephalopathies (EE), are a group of age-related disorders characterized by intractable seizures and electroencephalogram (EEG) abnormalities that may result in cognitive and motor delay. Early infantile epileptic encephalopathies (EIEE) manifest in the first year of life. EIEE are highly heterogeneous genetically but a genetic etiology is only identified in half of the cases, typically in the form of de novo dominant mutations. Method: This is a descriptive retrospective study of a consecutive series of patients diagnosed with EIEE from the participating hospitals. A chart review was performed for all patients. The diagnosis of epileptic encephalopathy was confirmed by molecular investigations in commercial labs. In silico study was done for all novel mutations. A systematic search was done for all the types of EIEE and their correlated genes in the literature using the Online Mendelian Inheritance In Man and PubMed databases. Results: In this case series, we report 72 molecularly characterized EIEE from a highly consanguineous population, and review their clinical course. We identified 50 variants, 26 of which are novel, causing 26 different types of EIEE. Unlike outbred populations, autosomal recessive EIEE accounted for half the cases. The phenotypes ranged from self-limiting and drug-responsive to severe refractory seizures or even death. Conclusions: We reported the largest EIEE case series in the region with confirmed molecular testing and detailed clinical phenotyping. The number autosomal recessive predominance could be explained by the society's high consanguinity. We reviewed all the EIEE registered causative genes in the literature and proposed a functional classification.