Shared Disease Mechanisms in Neurodevelopmental Disorders: A Cellular and Molecular Biology Perspective

Neurodevelopmental disorders (NDDs) are defined as a group of conditions that result from impaired brain development. Disorders that are commonly classified under NDDs include intellectual disability (ID), autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), communication and learning disorders, developmental delay (DD), brain malformations, cerebral palsy, Down syndrome, schizophrenia, and childhood epilepsies. A significant hinderance in the development of targeted treatments for NDDs are gaps in understanding how underlying genetic changes alter cellular physiology and how these changes may converge or diverge across NDDs with similar symptoms. Here, we focus on the genetic overlap between epilepsy, ASD, and other NDDs to identify common cellular and molecular mechanisms that may inform future treatments for each of these disorders individually or together. We describe several genes-including <i>CDKL5, TSC1/2, SCN1a,</i> and <i>TANC2</i>-that have been associated with epilepsy, ASD, or other NDD phenotypes that play a critical role in regulating one or more stages of brain development or function but differ widely in their disease-causing mechanisms. We also describe genotype-phenotype relationships. Finally, how a gene may cause NDDs through distinct functional pathways, or where different types of pathogenic variants within the same gene can have significantly different phenotypic outcomes is detailed.