A method and kit for determining the responsiveness of a human to vitamin treatment of migraine is provided, wherein an A66G methionine synthase reductase (MTRR) genotype indicates the responsiveness of a human to B complex vitamin treatment of migraine. AG heterozygotes and AA homozygotes have a relatively increased responsiveness to vitamin treatment of migraine. A GG genotype is indicative of a relatively reduced or lower responsiveness to vitamin treatment compared to an A allele carrier. The method and kit may detect an isolated nucleic acid or an encoded protein, due to a methionine/isoleucine polymorphism encoded by the A66G polymorphism. A method of treatment of migraine using vitamins is also provided, wherein the responsiveness of the patient to vitamin treatment has been assessed by determining the patients A66G genotype. The vitamins are typically vitamin B6, vitamin B12 and folic acid.
