Increase in urinary purines and pyrimidines in patients with methylmalonic aciduria combined with homocystinuria

Background: Methylmalonic aciduria combined with homocystinuria (MMA–HC) is the biochemical trait of a metabolic disorder resulting from impaired conversion of dietary cobalamin (cbl, or vitamin B12) to its two metabolically active forms. Effects on urinary purine and pyrimidine levels have not been described for this condition. Methods: Urine samples were collected from three patients with methylmalonic aciduria combined with homocystinuria and from 70 healthy subjects. Urinary purine and pyrimidine levels were quantitated by the use of LC/UV–Vis and LC/ESI/MS. Results: Higher urine levels of pyrimidines were detected with both methods in patients compared to controls. Conclusion: Methylmalonic aciduria with homocystinuria is due to deficiency of the enzyme, cobalamin reductase. The enzyme defect leads to altered hepatic metabolism, which appears to modify circulating pyrimidine levels.