I have a genetic SNP - single nucleotide polymorphism - 2 actually - that prevent me from metabolizing folic acid properly so that my body can break down homocysteine.  As a result, I am at increased risk for stroke, heart attack, Alzheimer's, and macular degeneration.  However, with l-methylfolate (the folic acid metabolic product the body needs), and the most active forms of B6 and B12, I have been able to reduce my homocysteine level from 15 to below 5 (normal).  Approximately 30% of the population is incapable of metabolizing folate properly.  10% of the population has a severe problem making the bioactive folic acid ingredient, l-methylfolate, the body needs to break down homocysteine.  My prediction is that in the next decade homocysteine levels will be monitored with the same religious fervor that we now invoke monitoring cholesterol levels.