We present a case of intracellular vitamin B12 deficiency presenting with confusion, subacute combined degeneration of the cord, megaloblastic anaemia and intrinsic factor antibodies in the serum.
Several syndromes present with megaloblastic anemia such as congenital megaloblastic anemia due to intrinsic factor defect and juvenile megaloblastic anemia with proteinuria due to defects in the cubilin or the amnionless protein.
Congenital intrinsic factor (IF) deficiency is a disorder characterized by megaloblastic anemia due to the absence of gastric IF (GIF, GenBank NM_005142) and GIF antibodies, with probable autosomal recessive inheritance.
Methylenetetrahydrofolate dehydrogenase (MTHFD1) deficiency has recently been reported to cause a folate-responsive syndrome displaying a phenotype that includes megaloblastic anemia and severe combined immunodeficiency.
Methionine synthase reductase (MTRR) is the locus of the cblE class of inborn errors of cobalamin metabolism that is characterized by megaloblastic anemia and homocystinuria.
Methionine synthase reductase (MSR) deficiency is an autosomal recessive disorder of folate/cobalamin metabolism leading to hyperhomocysteinemia, hypo- methioninemia and megaloblastic anemia.
Interaction between methionine synthase isoforms and MMACHC: characterization in cblG-variant, cblG and cblC inherited causes of megaloblastic anaemia.
Patients of the cblE complementation group of disorders of folate/cobalamin metabolism who are defective in reductive activation of methionine synthase exhibit megaloblastic anemia, developmental delay, hyperhomocysteinemia, and hypomethioninemia.