Mutations in the exocyst component EXOC2 (Sec5) cause severe defects in human brain development

The exocyst is an octameric protein complex and an essential component of the membrane transport machinery required for tethering vesicles at the plasma membrane prior to fusion. Here we report on pathogenic variants in one of the exocyst subunits, EXOC2 (Sec5), in unrelated families. Analysis of patient’s fibroblasts revealed reduced protein levels in Family 1, impaired secretory vesicle fusion with the plasma membrane and defective bulk exocytosis. Based on genetic and functional genomics findings, we suggest that the EXOC2 variants we have identified are the cause of the neurological disorder in these patients.