CblC Type Methylmalonic Aciduria with a Novel Homozygous Mutation: A Case Report

Background Combined Methylmalonic Aciduria (MMA), and homocystinuria CblC type is the most common inborn error of cobalamin metabolism with 77 mutations identified till date in the MMACHC gene. The disease has early and late presentations with varied clinical features. Case report A pair of preterm monochorionic twins was born to non-consanguineous parents with history of 2 previous infant deaths with suspected MMA. The twins became symptomatic in second week with severe neutropenia, thrombocytopenia, progressive encephalopathy and eczema without anemia, metabolic acidosis or hyperammonemia. Investigation revealed elevated plasma Complement 3 (C3) acyl carnitine and very high MMA levels in urine. Genetic testing revealed a novel large deletion mutation in chromosome 1 which comprised of the whole MMACHC gene confirming the diagnosis of CblC type of MMA. The mutation was homozygous despite parents being unrelated and was identified in both parents later. Both twins responded transiently to treatment with hydroxycobalamin. Conclusion Large deletion in the MMACHC gene which was identified in a homozygous state in our twins is previously unreported. The phenotypic features are described.