Dravet syndrome (DS) is a rare and severe form of epilepsy that causes intellectual disability and motor deficits and can lead to premature death. A loss-of-function mutation in one copy of SCN1A, encoding the voltage-gated sodium channel (NaV)1.1 α subunit, is the most frequent alteration found in DS patients and has been linked with inhibitory neuron dysfunction. Despite the potential of gene therapies, AAV-mediated SCN1A gene replacement for DS has not been possible yet due to AAV genome size constraints.

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease originating from biallelic pathogenic variants in the ARSA gene, mainly affecting young children.