Letters to the Editor 323 RE: "MATERNAL VITAMIN USE, GENETIC VARIATION OF INFANT METHYLENETETRAHYDROFOLATE

We welcome the article by Shaw et al. (1), which explored for the first time how maternal periconceptional vitamin use and having a specific gene variant of a folate-related gene may jointly affect an infant's risk for spina bifida. The authors concluded that there is little evidence of an interaction between an infant's genotype and maternal vitamin use. We submit that their data are also consistent with a different scenario, in which vitamin use and genotype interact in determining the infant's risk for spina bifida, and that their study was too small to establish which of the two scenarios is correct. We drew these conclusions after exploring the data from Shaw et al. (1) using a 2 x 4 table in which case and con-trol infants were classified according to MTHFR genotype and maternal vitamin use (table 1). We computed odd