Define Excretion of Methyl malonic acid in urine (Methyl malonil aciduria)?

Methyl malonic acid is found only in traces in normal urine (1-2 mg/day). In vitamin  B₁₂ deficiency (pernicious anaemia), the excretion of methyl malonic acid in  urine increases to about 100 to 200 mg/day due to the absence of vitamin B₁₂  co-enzyme (methyl malonyl CoA isomerase) involved in the conversion methyl  malonyl CoA to succinyl CoA. This is a sensitive method for assessing vitamin B _l2 deficiency.

Before we end our discussion on vitamin B₁₂ we would like to highlight that  vitamin B₁₂interaction with folate or folic acid is very important from the human  nutrition point of view. We have already emphasized earlier under the folate action that the vitamin B₁₂- dependent enzymes, methionine synthase, functions in one of the two folate cycles, namely, the methylation cycle. Interruption of the cycle reduces the level of S-adenosylmethionine. This occurs in pernicious anaemia and other causes of vitamin B₁₂ deficiency, producing as a result demyelination of the peripheral nerves and the spinal column, giving rise to the clinical condition called   sub acute combined degeneration. This neuropathy is one of the main presenting conditions in peinicious anaemia. The other principal presenting condition in PA is a megaloblastic anaemia mor- hologically identical to that seen in folate deficiency.  Disruption of the methylation cycle also causes a lack of DNA biosynthesis and anaemia.

With this, we end our study of vitamin B₁₂ and also our study of the B- complex vitamins. Finally let us review the other water soluble vitamin i.e. ascorbic acid.