Preprint · Jun 15, 2026
Prevalence of epilepsy and young-onset dementia in adults with intellectual disability: Contrasting Down syndrome and autism diagnoses
By Lee N, Tao S, Voltaire S et al.
Objective: Epilepsy and young-onset Alzheimer’s disease and related dementias [ADRD] greatly impact health and service needs. Despite their elevated prevalence in intellectual disability (ID), large scale studies of both conditions, which are known to co-occur, among subgroups of ID (i.e., Down syndrome [DS] and/or autism spectrum disorder [ASD]) are lacking. The objective of this research was to characterize the prevalence of epilepsy, young-onset ADRD, and their comorbidity in ID relative to the general population and to examine how co-occurring DS and/or ASD impacts prevalence.Methods: In this cross-sectional study of data from the Centers for Medicare and Medicaid Services (CMS; 2008-2019) from all 50 US States/District of Columbia, prevalence and odds ratios of epilepsy and young-onset ADRD were examined for all enrollees with ID between the ages of 30 and 64 years (n=847,430) and a random sample of age-matched adults from the general population without diagnoses of ID, ASD, or DS (n=1,065,530) representing both sexes and all racial/ethnic groups. Among those with ID, prevalence of these conditions was contrasted when individuals held diagnoses of DS and/or ASD.Results: Higher prevalence was observed in the ID group relative to the general population for epilepsy, young-onset ADRD, and their comorbidity. Among participants with ID, ASD was associated with the greatest epilepsy risk whereas DS was associated with the greatest risk for ADRD and epilepsy+ADRD. When DS and ASD diagnoses were considered together, interactions were observed, indicating subtle differences in the risk for these conditions among participants with both DS and ASD.Significance: These results support the importance of screening adults with ID for epilepsy and young-onset dementia. They also draw attention to subgroups of people with ID who may be at greater risk for these conditions, and the importance of evaluating the co-occurrence of these conditions among adults with ID.