STXBP1 and developmental and epileptic encephalopathy: 27 In comparison to STXBP1, which is closely related to STX1B (since the respective proteins interact with each other in the synaptic transmitter release machinery) and exhibits in most cases an early onset of epilepsy presenting as Ohtahara syndrome or West syndrome,28STX1B-related DEE shows a later onset of epilepsy after the first birthday.