STXBP2 and metabolic acidosis: Chronic diarrhoea is linked to familial hemophagocytic lymphohistiocytosis type 5 and metabolic acidosis in patients with syntaxin-binding protein 2 (STXBP2/MUNC18-2) mutation and to neurological impairments in patients with syntaxin 3 (STX3) mutation, respectively [20,21,22].