Vacuolar H+-ATPases (V-ATPases) transport protons across cellular membranes to acidify various organelles. ATP6V0A1 encodes the a1-subunit of the V0 domain of V-ATPases, which is strongly expressed in neurons. However, its role in brain development is unknown. Here we report four individuals with developmental and epileptic encephalopathy with ATP6V0A1 variants: two individuals with a de novo missense variant (R741Q) and the other two individuals with biallelic variants comprising one almost complete loss-of-function variant and one missense variant (A512P and N534D). Lysosomal acidification is significantly impaired in cell lines expressing three missense ATP6V0A1 mutants. Homozygous mutant mice harboring human R741Q (Atp6v0a1R741Q) and A512P (Atp6v0a1A512P) variants show embryonic lethality and early postnatal mortality, respectively, suggesting that R741Q affects V-ATPase function more severely. Lysosomal dysfunction resulting in cell death, accumulated autophagosomes and lysosomes, reduced mTORC1 signaling and synaptic connectivity, and lowered neurotransmitter contents of synaptic vesicles are observed in the brains of Atp6v0a1A512P/A512P mice. These findings demonstrate the essential roles of ATP6V0A1/Atp6v0a1 in neuronal development in terms of integrity and connectivity of neurons in both humans and mice.

The chromosome alignment maintaining phosphoprotein 1 (CHAMP1) gene has a key role in neurodevelopment. It is involved in kinetochore-microtubule attachment and in the regulation of chromosomes alignment during mitosis. So far, 17 cases of CHAMP1 mutations have been reported with a common clinical picture of developmental delay and intellectual disability, dysmorphic facial features, hypotonia and/or spasticity, and microcephaly. Four patients had epilepsy of whom three had focal seizures and one had generalized epilepsy. We report two new cases, which have in addition to developmental delay, refractory myoclonic epilepsy. These cases suggest that the phenotypic spectrum of CHAMP1 mutations may be broader and includes refractory myoclonic epilepsy as well.

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