So why might my SAH be so low?
So there are two types of things that could be happening:
1. the conversion that makes the SAH might be slowed down because of SNPs that affect the enzyme(s) that do(es) the conversions or because of a lack of one of the chemicals that are used up in the reaction, or
2. The SAH gets used up more quickly than normal, perhaps because of SNPs that make the enzyme more efficient, or because there is an excess of the chemicals that are used in the reaction, or because the end product gets used up, so there is always a need for that reaction to go.
Of course, there's likely more than one thing going on. Was your homocysteine tested at the same time? If it's also low, then I vote for reason #2. If it's high, I vote for reason #1.