Abstract
Lethal neonatal encephalopathies are heterogeneous congenital disorders that can be caused by mitochondrial dysfunction. Biallelic large deletions in the contiguous ATAD3B and ATAD3A genes, encoding mitochondrial inner membrane ATPases of unknown function, as well as compound heterozygous nonsense and missense mutations in the ATAD3A gene have been recently associated with fatal neonatal cerebellar hypoplasia. In this work, whole exome sequencing (WES) identified the novel homozygous variant c.1217 T > G in ATAD3A, predicting a p.(Leu406Arg) substitution, in four siblings from a consanguineous family presenting with fatal neonatal cerebellar hypoplasia, seizures, axial hypotonia, hypertrophic cardiomyopathy, hepatomegaly, congenital cataract, and dysmorphic facies. Biochemical phenotypes of the patients included hyperlactatemia and hypocholesterolemia. Healthy siblings and parents were heterozygous for this variant, which is predicted to introduce a polar chain within the catalytic domain of ATAD3A that shortens its beta-sheet structure, presumably affecting protein stability. Accordingly, patient's fibroblasts with the homozygous variant displayed a specific reduction in ATAD3A protein levels associated with profound ultrastructural alterations of mitochondrial cristae and morphology. Our findings exclude the causative role of ATAD3B on this severe phenotype, expand the phenotypical spectrum of ATAD3A pathogenic variants and emphasize the vital role of ATAD3A in mitochondrial biogenesis.