Altered synaptic connectivity in an in vitro human model of STXBP1 encephalopathy

Early infantile epileptic encephalopathies are devastating conditions, generally of genetic origin, but the pathological mechanisms often remain obscure. A major obstacle in this field of research is the difficulty of studying cortical brain development in humans, in utero. To address this, we established an in vitro assay to study the impact of gene variants on the developing human brain, using living organotypic cultures of the human subplate and neighbouring cortical regions, prepared from ethically sourced, 14-17 post conception week brain tissue (www.hdbr.org). We were able to maintain cultures for several months, during which time, the gross anatomical structures of the cortical plate, subplate and marginal zone persisted, while neurons continued to develop morphologically, and form new synaptic networks. This preparation thus permits the study of genetic manipulations, and their downstream effects, upon an intact developing human cortical network. We focused upon STXBP1 haploinsufficiency, which is among the most common genetic causes of infantile epileptic encephalopathy. This was induced using shRNA interference, leading to impaired synaptic function and a drop in the number of glutamatergic synapses. We thereby provide a critical proof-of-principle for how to study the impact of any gene of interest on the development of the human cortex.