Methylmalonic aciduria due to a new defect in adenosylcobalamin accumulation by cells.

A child with methylmalonic aciduria due to failure to accumulate adocbl in mitochondria has a phenotype similar to cblA disease. Deficient utilization of labeled propionate by his fibroblasts is corrected by their fusion with those from cblA patients, indicating that he belongs to a different complementation class and probably is deficient in a different gene product. The defect appears not to be due to reduced affinity of enzymes for adocbl, or for ATP, and the minimal thiol required for adocbl synthesis is not different from that of extracts of normal cells.