Abstract: The present invention relates to an alanine glyoxylate aminotransferase (AGXT) I340M therapeutic for use as a medicament or in a method of treatment, for example in the treatment of an AGXT-responsive condition. The AGXT I340M therapeutic is an AGXT I340M protein comprising an amino acid sequence, which, when optimally aligned with SEQ ID NO: 2, comprises a methionine at a position corresponding to position 340 in SEQ ID NO: 2, a nucleic acid molecule encoding such an AGXT I340M protein, or a virion of a viral gene therapy vector comprising such a nucleic acid molecule. The AGXT I340M therapeutic has a higher specific activity as compared to other AGXT alleles and may therefore be advantageously used in the treatment of primary hyperoxaluria type I.