The breakdown of methylmalonic acid yields fatty acids necessary for the formation of myelin. Has anyone measured the level of methylmalonic acid in demyelinating diseases, such as multiple sclerosis (MS)? Since vitamin B12 plays an instrumental role in breaking down homocysteine and methylmalonic acid, might this be the basis for the link between B12 deficiency and MS?
—Joseph H. Villalon, MD, Walsenburg, Colo.
Methylmalonic acid and serum cobalamin have been measured in patients with MS, but the results have been disappointing. Although studies from the early 1990s observed that patients with MS may have lower serum cobalamin levels than controls, suggesting a possible pathologic association, there is no clear evidence that this has any clinical relevance. One study demonstrated that although 32 of 156 patients with either clinically definite or clinically probable MS had low measured serum cobalamin, only seven of these 32 patients had elevated homocysteine—and only one of those also had elevation of methylmalonic acid (Arch Neurol. 1994;51:1110-1114). In clinically significant vitamin B12 deficiency, both markers should rise. Another study concluded that there was no apparent association between B12 deficiency and MS at all (Mult Scler. 2003;9:239-245).
—Daniel G. Tobin, MD (116-24)