What is the role of abnormalities of cellular use in the etiology of pernicious anemia?

Updated: Feb 18, 2019
  • Author: Srikanth Nagalla, MD, MS, FACP; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

The seven abnormalities of cellular use, commonly denoted by letters A through G, can be detected by the presence or absence of methylmalonic aciduria and homocystinuria. The presence of only methylmalonic aciduria indicates a block in conversion of methylmalonic CoA to succinyl CoA and results in either a genetic deficit in the methylmalonyl CoA mutase that catalyzes the reaction or a defect in synthesis of its CoA cobalamin (cobalamin A and cobalamin B deficiency).

The presence of only homocystinuria results either from poor binding of cobalamin to methionine synthase (cobalamin E deficiency) or from producing methylcobalamin from cobalamin and S adenosylmethionine (cobalamin G deficiency). This results in a reduction in methionine synthesis, with pronounced homocystinemia and homocystinuria.

Methylmalonic aciduria and homocystinuria occur when the metabolic defect impairs reduction of cobalamin III to cobalamin II (cobalamin C, cobalamin D, and cobalamin F deficiency). This reaction is essential for formation of both methylmalonic acid and homocystinuria.

Early detection of these rare disorders is important because most patients respond favorably to large doses of cobalamin. However, some of these disorders are less responsive than others, and delayed diagnosis and treatment are less efficacious.


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