STXBP1 and Encephalopathy: Individuals with protein truncating variants seem to have similar clinical presentations when compared in a large cohort with STXBP1 encephalopathies, suggesting a shared pathological aetiology.10 It seems likely that the effects of STXBP1 haploinsufficiency arise prenatally, supported by the observation that STXBP1 is highly expressed in the developing subplate.6 The study of functional prenatal interactions, however, presents a major practical challenge for early human development.