Base-edited cynomolgus monkeys mimic core symptoms of STXBP1 encephalopathy.

Presynaptic syntaxin binding protein 1 (STXBP1) is essential for neurotransmitter release. Heterozygous mutations in this protein cause STXBP1 encephalopathy (STXBP1-E), which is characterized by intellectual disabilities and epilepsies. Since nonhuman primates closely resemble humans, monkey models may advance studies on the pathogenesis and therapeutic treatments of STXBP1-E. We generated cynomolgus monkeys carrying STXBP1 (R292H) mutation through base editing of in vitro fertilized embryos to mimic a clinical condition. The newborn STXBP1-edited monkeys exhibited focal epilepsy, and the animal that survived beyond the first week postpartum presented typical EEG phenotypes. Biochemical analysis of brain biopsy samples showed reduced levels of STXBP1 (MUNC18-1) and SNARE complex proteins. Single-cell sequencing identified one specific cell cluster that may contribute to encephalopathy. Thus, our case report shows that base-edited STXBP1 mutant monkeys are a good animal model for STXBP1-E, and that a base-editing approach is useful for generating primate models of human genetic disorders.