SZT2 and Epileptic encephalopathy: Interestingly, biallelic variants in SZT2 also cause a distinct NDD, characterized by severe early-onset epileptic encephalopathy, global developmental delay, structural brain abnormalities and frequent macrocephaly.16,17 In mice, Szt2 loss-of-function (LoF) mutants display seizure susceptibility and increased mTORC1 signalling in the brain.15,33