Clinical and biochemical observations in a patient with combined Pompe disease and cblC mutation

Metabolic studies are described in a patient who presented at 3 weeks of age with severe anaemia, hyperbilirubinaemia and hypotonicity. Clinically, glycogen storage disease type II (Pompe disease) was suspected because of a massively enlarged heart and hepatosplenomegaly. This was confirmed biochemically by the demonstration of glycogen accumulation in skeletal muscle and undetectable acid α-1,4-glucosidase activity in fibroblasts. Further biochemical studies in this patient surprisingly revealed homocystinuria and methylmalonic aciduria, suggesting a defect in the uptake, transport or intracellular metabolism of vitamin B12. Studies in cultured fibroblasts from the patient revealed a low uptake of [57Co]cyanocobalamin and an impaired intracellular conversion to both 5′-deoxyadenosylcobalamin and methylcobalamin. Moreover, the incorporation of labelled propionate into proteins as well as the formation of labelled methionine from labelled 5-methyltetrahydrofolate was deficient in fibroblasts from the patient. Complementation studies revealed the presence of the cblC mutation in this patient. No treatment was initiated and the patient died at the age of 31 days. We conclude that the patient was affected by both glycogen storage disease type II and cblC disease. The remarkable combination of these two rare inborn errors can be the result of the consanguinity of the parents.