CYFIP2 p.Arg87Cys Causes Neurological Defects and Degradation of CYFIP2

Here, we report the generation and comprehensive characterization of a knockin mouse model for the hotspot p.Arg87Cys variant of the cytoplasmic FMR1‐interacting protein 2 ( CYFIP2 ) gene, which was recently identified in individuals diagnosed with West syndrome, a developmental and epileptic encephalopathy. The Cyfip2 +/R87C mice recapitulated many neurological and neurobehavioral phenotypes of the patients, including spasmlike movements, microcephaly, and impaired social communication. Age‐progressive cytoarchitectural disorganization and gliosis were also identified in the hippocampus of Cyfip2 +/R87C mice. Beyond identifying a decrease in CYFIP2 protein levels in the Cyfip2 +/R87C brains, we demonstrated that the p.Arg87Cys variant enhances ubiquitination and proteasomal degradation of CYFIP2. ANN NEUROL 2023;93:155–163