Folic acid dependent hypersarcosinaemia.
Hypersarcosinaemia is a rare inborn error of metabolism, caused by a deficiency of the sarcosine dehydrogenase complex with tetrahydrofolate as a formaldehyde acceptor needed for the sarcosine-glycine conversion. Prolonged therapy with folic acid on a hypersarcosinaemic patient resulted in a significant effect on the urinary excretion of sarcosine, leading to the conclusion that the patient has a folic acid dependent hypersarcosinaemia.