Project Summary Epilepsy and migraine have long been recognized as being linked in certain families, but the genetic basis of this comorbidity in not well understood. We and others have recently found evidence in human genetic studies that variation in GPR37L1 is a major contributor to epilepsy and migraine risk, especially in cases where epilepsy and migraine are comorbid. GPR37L1 is expressed predominantly in astrocytes, and thus studies on this receptor may lead to more general insights into how astrocyte dysfunction contributes to epilepsy and migraine. The goal of this project is to elucidate the cellular and mechanistic basis by which GPR37L1 regulates seizure and migraine susceptibility. We will assess the trafficking and signaling properties of disease-associated GPR37L1 variants in astrocytes and also address the mystery of why GPR37L1 signaling appears to be dependent on the astrocytic context. Furthermore, we will study the seizure vulnerability of knock-in mice harboring pathogenic human variants and also explore how astrocyte development in human cortical organoids is affected by pathogenic variants of GPR37L1. Additionally, we will assess mice lacking Gpr37L1 or expressing pathogenic Gpr37L1 variants for migraine-relevant phenotypes and evaluate these mutant mice for changes in cortical circuit excitability that might inform both the migraine and seizure phenotypes. These studies will provide novel insights into the fundamental biology of GPR37L1 and also pave the way for the development of novel GPR37L1-targeted therapeutics for the treatment of epilepsy, migraine and other diseases.