A. methyl donors B. No. Trans-sulfuration can produce sulfates but is NOT the only way to make sulfates. If you are CBS positive I am not saying it is impossible but it seem unlikely you will be low in sulfates unless you have genetic defects elsewhere that block making sulfates. So I would advise testing. Maybe you are low. But then your CBS gene is somehow not being expressed much and that would be wonderful to have for a homozygote. Edit: You are homozygote A360A! Never mind that is probably why. The other one is far more deleterious (the C667T). Dr Yasko pulls too many satellite SNPs in for my taste. A360A has been largely debunked as a problem at least on its own. Congratulations. Testing for urine sulfates may help you identify if you are low though. The best way for what you suspect is a 24 hour urine sulfate test through LabCorp or the equivalent.