Neural tube defects--why are rates high among populations of Mexican descent?

The literature indicates that prevalence of neural tube defects (NTD) is more common among Mexican than Caucasian populations in North America. Combining data from Mexico and the California Birth Defects Monitoring Program shows that there is a gradient of risk, with prevalences highest in Mexico, lowest among U.S. Caucasians, and intermediate among populations of Mexican descent in the United States. The reason for this risk gradient is unknown. While folic acid in combination with multivitamins has consistently been shown to protect against NTD among Caucasian populations, little information has been published about this relationship among Hispanic populations. We present some limited evidence suggesting that lack of folic acid does not account for the risk gradient in NTD prevalences. There is an urgent need for epidemiologic case-control studies comparing risks for NTD in Mexico and among populations of Mexican and Caucasian descent in the United States. There is ample evidence that 4 mg of folic acid given during the periconceptional period prevents neural tube defects (NTDs), specifically anencephaly and spina bifida (1). There also have been several observational studies demonstrating that folic acid in combination with multivitamins results in approximately a 50% reduction in NTDs (2-5). A recent clinical trial in Hungary showed that 0.8 mg of folic acid, in combination with multivitamins, given periconceptionally protects against the first occurrence of NTDs (6). Together this