STXBP1 and Ataxia: Of particular interest is Syntaxin-binding protein 1 (STXBP1), an essential pre-synaptic protein also called MUNC18-1 (Mammalian uncoordinated-18),5 that is highly expressed in the prenatal developing brain.6 Loss of function variants in STXBP1, collectively termed ‘STXBP1 encephalopathies’, result in significant intellectual disability without regression, early-life onset epilepsy in most, and a range of movement disorders including ataxia, tremor and spasticity,7–9 but the underlying pathological mechanisms are poorly understood.