When Monogenic Isn’t Monogenic—Unravelling the Oligogenic Architecture of the Developmental and Epileptic Encephalopathies

Abstract

Comprehensive Analysis of Coding Variants Highlights Genetic Complexity in Developmental and Epileptic Encephalopathy Takata A, Nakashima M, Saitsu H, et al. Nat Commun. 2019;10(1):2506. doi:10.1038/s41467-019-10482-9. www.nature.com/naturecommunications. Although there are many known Mendelian genes linked to epileptic or developmental and epileptic encephalopathy (EE/DEE), its genetic architecture is not fully explained. Here, we address this incompleteness by analyzing exomes of 743 EE/DEE cases and 2366 controls. We observe that damaging ultra-rare variants (dURVs) unique to an individual are significantly overrepresented in EE/DEE, both in known EE/DEE genes and the other non-EE/DEE genes. Importantly, enrichment of dURVs in non-EE/DEE genes is significant, even in the subset of cases with diagnostic dURVs (P = 0.000215), suggesting oligogenic contribution of non-EE/DEE gene dURVs. Gene-based analysis identifies exome-wide significant (P = 2.04 Å∼ 10−6) enrichment of damaging de novo mutations in NF1, a gene primarily linked to neurofibromatosis, in infantile spasm. Together with accumulating evidence for roles of oligogenic or modifier variants in severe neurodevelopmental disorders, our results highlight genetic complexity in EE/DEE and indicate that EE/DEE is not an aggregate of simple Mendelian disorders.