Disorders of Cobalamin and Folate Transport and Metabolism

The serum cobalamin (Cbl) level is usually low in patients with disorders affecting absorption and transport of Cbl, with the exception of transcobalamin (TC) deficiency. Patients with disorders of intracellular Cbl metabolism typically have normal serum Cbl levels, although levels may be reduced in the cblF disorder. Homocystinuria and hyperhomocysteinaemia, as well as megaloblastic anaemia and neurological disorders, are major clinical findings in patients with disorders of cobalamin absorption and transport, as well as those with defects of cellular metabolism that affect synthesis of methylcobalamin (MeCbl). Methylmalonic aciduria and acidaemia, resulting in metabolic acidosis, are seen in disorders that result in decreased synthesis of adenosylcobalamin (AdoCbl).