Molecular and functional characterization of new pathogenic mutations in mitochondrial ornithine and aspartate/glutamate transporters

Mutations in the SLC25A13 gene, coding for a liver-specific isoform of the mitochondrial aspartate/glutamate carrier (AGC2), and in the SLC25A15 gene, coding for ornithine carrier isoform 1 (ORC1), cause type 2 citrullinemia (CTLN2) and hyperornithinemia–hyperammonemia–homocitrullinuria (3H syndrome), respectively. The aim of this work was to identify and characterize novel mutations of these two genes in patients presenting symptoms suggestive of AGC2 or ORC1 deficiency. In the AGC2 transcript of a Pakistani man living in Europe suspected of being affected by CTLN2 (a highly prevalent disease in Southeast Asia), a homozygous mutation, c.1763GNA, was found which produces an R588Q change in the protein. In the ORC1 transcript of patients suspected of 3H syndrome andhaving different ethnic origin, six new homozygous mutations (c.110TNG, c.212TNA, c.337GNT, c.815CNT, c.818TNA and c.847CNT) were found that produce M37R, L71Q, G113C, T272I, M273K and L283F substitutions, respectively, in the protein. Each mutation was functionally characterized in liposomes reconstituted with AGC2 or ORC1 carrying the above-mentioned amino acid replacement. They all reduced transport activity by approximately 90% in comparison to the activity of the wild-type proteins suggesting that they are diseasecausing mutations.