Have you ever noticed that some families seem — it's hard to find a nice way to put it — a little odd? Although genetics are just a part of any psychiatric disorder, some families carry genes that in combination with lifestyle increase the frequency of autism, bipolar disorder, schizoaffective disorder, and schizophrenia.
Sometimes the problem is the MTHFR mutation that affects the coding of the DNA sequence that directs the protein sequence of methylenetetrahydrofolate reductase, an enzyme essential for the body to use vitamin B9 (folate) efficiently. Sometimes it's both an MTHFR mutation and cystathionine β synthase (CβS), transcobalamin 2 receptor (TCN2) and methionine synthase reductase (MTRR) mutations, which affect the way the brain can use vitamin B6, vitamin B12, and the amino acid methionine. Add these genetic problems to bad diet (bad diets tend to run in families, too) and environmental stresses, and mental illness results. 
Women who lose their babies over and over again
But maybe mental illness isn't a problem. Have you ever known women who seem to lose their babies over and over again by miscarriage? In an earlier era, these women would have been told it was somehow their fault. The real reason for spontaneous abortion (that is, abortion that isn't performed by either the woman or the doctor, that just happens) often is problems in the embryo's developing brain and nervous system. These defects in development that lead a woman's body to reject her own child can be caused by defects in enzymes for the use of vitamins B9 (folic acid, also known as folate) and B12.  The heartbreak of losing a wanted child tends to be something that is very literally passed down from both parents to their daughters and mothers even to unborn children. This severe problem affects about one in one hundred to one in fifty women .
What about heart disease?
Some people have great cholesterol, get their exercise, and first learn of heart disease through sudden death. An MTHFR mutation is never the only cause, but it's noted in about one in five autopsies .
Or stroke? In men, especially in Asian men, MTHFR mutations are a significant risk factor for stroke .
In African and African-American men, an MTHFR mutation is a major risk factor for vascular complications of diabetes, the kinds of problems that include not just heart attack or stroke but also amputation of limbs .
How to get the right amount of vitamin B9 if you have an MTHFR mutation?
It's a little tricky to get the right amount of the right kind of vitamin B9 if you have an MTHFR mutation. There are four different kinds of MTHFR mutations, but the following information applies no matter which MTHFR mutation you have, or if you have no MTHFR mutation, or you just don't know because you haven't had the MTHFR gene test.
- Folate is a water-soluble vitamin, but more isn't always better. If you have a MTHFR mutation, getting more than 1000 micrograms (mcg) of any kind folate per day is toxic. If you don't have an MTHFR mutation, it's just not helpful, but if you don't know, it's best to treat a high dose of folic acid as something that could be bad for you.  Too much of the wrong kind of folate keeps your cells, particularly your brain cells, from absorbing the kind you need. Not getting the right amount of omega-3 essential fatty acids, either too much or too little (more than 10,000 mg a day or less than 1,000 mg a day) makes the problem worse .
- If you have an MTHFR mutation, your body can use "regular" folic acid, just not efficiently enough for good health. You may not be diagnosed with a deficiency disease, but a combination of genetics and lifestyle choices greatly increase your risk for cardiovascular, endocrine, psychiatric, and neurological conditions.
- Even if your body can't use folic acid in supplements, it can use the form of folic acid known as methylfolate . In North America, it's been branded as Quatrefolic, but you don't need to buy the brand name. Any product that contains "methylfolate" will do.
- There's a new measurement system for folic acid. The old system gave the weight of the food form of the vitami, folate, and the supplement or food additive form of the vitamin, folic acid, in micrograms (mcg). The new system takes into account that synthetic folic acid is about 70 percent easily absorbed by the body than the folate in food. It measures doses in dietary folate equivalents, or DFE's. You need 400 mcg of folic acid or methylfolate, equivalent to 680 mcg DFE's per day. Anything over 589 mcg (by weight) or 1000 mcg DFE's by the new measurement system, should be treated as if it would be toxic. 
- Many brands of folic acid supplements contain potentially toxic levels of the vitamin. As they are formulated at the time of the writing of this article, a quick check of label data shows that Bariatric Advantage Chewable Multi-Formula, Enfamil Expecta, Natural Factor's Men's 50+ Multistart by Dr. Michael Murray, Nature Made Multi for Her, Nature's Way Alive! Whole Foods Energizer, USANA Essentials Mega Antioxidant, Thorne Research AI's Formula, and VitaFusion Prenatal, among other brands, contain more B9 than the FDA now says is safe. These aren't bad brands in general. They just contain too much folic acid, even the good kind, for people who have MTHFR mutations.