Pyridoxine Responsiveness in a Type 1 Primary Hyperoxaluria Patient With a Rare (Atypical) AGXT Gene Mutation
Prince Singh, Fouad T. Chebib, Andrea G. Cogal, Dimitar K. Gavrilov, Peter C. Harris, John C. Lieske
Abstract
Primary hyperoxaluria (PH) refers to a group of genetic disorders that result from increased endogenous production of oxalic acid. Type 1 PH (PH1) is the most common and most severe form, and is caused by deficiency or loss of the liver-specific, vitamin-B6−dependent peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT) encoded by the AGXT gene.1 This results in overproduction and excessive urinary excretion of oxalate that can then cause recurrent kidney stones and nephrocalcinosis.S1 Vitamin B6 (pyridoxine) responsiveness, as assessed by a decrease in urinary oxalate excretion by 30% or more while on pyridoxine in pharmacologic doses of 5-10 mg/kg/day, has been most clearly associated with 2 mutations in the AGXT gene: c.508G>A (p.Gly170Arg) which accounts for approximately 30% of cases in North America, and more rarely c.454T>A (p.Phe152Ile), but not for c.121G>A (p.Gly41Arg).