Epidemiology of Developmental and Epileptic Encephalopathy and of Intellectual Disability and Epilepsy in Children

We aimed to determine the population-based cumulative incidence and prevalence of developmental and epileptic encephalopathies (DEEs) and intellectual disability and epilepsy (ID+E) in children. We analyzed the cumulative incidence of specific epilepsy syndromes.Children under 16 years with a DEE or ID+E were ascertained using EEG records from 2000-2016 in the Wellington region of New Zealand. Epilepsy syndromes were diagnosed on medical record and EEG review. Point prevalence and cumulative incidence were calculated, and cumulative incidence for each epilepsy syndrome.The cohort comprised 235 children (58% male) with developmental impairment and epilepsy, including 152 (65%) with DEE and 83 (35%) with ID+E. Median age of seizure onset was 15.4 months (range day 1 - 15 years). Median follow-up from seizure onset was 7.9 years (range 0-18.2 years). Point prevalence for the broad group of children with epilepsy and developmental impairment was 175/100,000 children (95% CI 149-203; DEE 112 and ID+E 63/100,000 children). Cumulative incidence for DEE was 169/100,000 children (CI 144-199) and for ID+E was 125/100,000 (CI 95.4-165). Cumulative incidence per 100,000 children was: infantile epileptic spasms syndrome 58.2 (CI 45.0-75.3), epilepsy with myoclonic-atonic seizures 16.4 (CI 9.69-27.7), Lennox-Gastaut syndrome 13.2 (CI 4.1-41.9), and Dravet syndrome 5.1 (CI 2.1-12.2). 50/152 (33%) of children with DEE and 70/83 (84%) with ID+E could not be diagnosed with a known epilepsy syndrome.Epilepsy and developmental impairment prior to age 16 years occurs in 1 in 340 children, with 1 in 590 having a DEE and 1 in 800 ID+E. These individuals require significant health and community resources, therefore these data will inform complex health service and education planning. Epidemiological studies have focused on early childhood onset DEEs. These do not fully reflect the burden of these disorders as 27% of DEEs and 70% of ID+E begin later, with seizure onset after 3 years. Understanding the cumulative incidence of specific syndromes together with the broad group of DEEs is essential for planning of therapeutic trials. Given trials focus on specific syndromes there is a risk that effective therapies will not be developed for 1/3 of children with DEE.