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Dear Dr. Roach: I keep hearing that I should have my children tested for the MTHFR gene before vaccinating them. What is the MTHFR gene? Does something about it lead to more vaccine injuries?

K.S.H.

Dear K.S.H.: The MTHFR gene codes for the enzyme methylenetetrahydrofolate reductase, an important enzyme in making the active form of folic acid.

About 10 to 15 percent of North Americans (higher in people of Hispanic or Italian descent) have a particular mutation in this gene (called the C677T, or “thermolabile” mutation). People with this mutation are at higher risk for low active folic acid, which can cause a high blood level of homocysteine. This, in turn, is associated with an increased risk of blood clots and coronary artery disease.

I should note that it isn’t having the gene that seems to put people at risk, but the presence of high levels of homocysteine. However, in a review of eight trials of people with high homocysteine levels who were treated with folic acid and other vitamins, there was no benefit in terms of decreasing blood clots, heart disease, cancer or death, despite the effectiveness of the supplements in lowering homocysteine levels. There is theoretical evidence that methylfolate may be more effective than regular folic acid at reducing homocysteine levels, but there still is no evidence that treatment reduces clinical risk.

There also is no evidence that people with MTHFR mutations are at higher risk during routine vaccination, and genetic testing for MTHFR mutations is currently not recommended by the American College of Medical Genetics and Genomics. I did find a paper showing that people with MTHFR gene mutations had a roughly doubled risk of fever, rash or enlarged lymph nodes from smallpox vaccine (which has a very high risk of adverse effects relative to routine child or adult immunizations).

I don’t recommend testing. For people who know that they have a MTHFR mutation, it is reasonable to take a vitamin containing active forms of folic acid and vitamin B-12. As far as routine immunization goes, because of the far greater benefit than risk, I recommend the vaccines for all people with or without MTHFR mutations, despite any theoretical increased risk in side effects.

Dear Dr. Roach: My doctor gave me free samples of Cialis. It was very effective, and I had no side effects. I travel to Mexico a lot, so I picked up Cialis there (which doesn’t need a prescription). The tablets were 40 milligrams, the same as the Cialis my doctor gave me. These tablets had basically NO effect, even in larger dosages.

Do all the same medications, no matter where they come from, contain the same amount of medication? In other words, can I be sure the Cialis I had in the U.S. is the same exact Cialis I picked up in Mexico? Seems like there were TOTAL differences in effect.

S.S.

Dear S.S.: Although the exact drug Cialis (and many others) can be purchased in Mexico, sometimes at huge savings, there can be problems both with the storage of the drugs (extreme heat can decrease potency) and with actual counterfeit drugs. U.S. citizens are allowed to bring into the country a three-month supply of medications (but not controlled substances). The Food and Drug Administration carefully monitors prescription drugs sold in the U.S., but it has no jurisdiction in Mexico. Purchasing brand-name drugs from reputable pharmacies is your best chance of avoiding fake drugs, but there is still a chance that you aren’t getting what you pay for.

Email questions to ToYourGoodHealth@med.cornell.edu.

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