Association studies for specific candidate genes, selected because of their known biological function relevant to AD, have been performed for over 350 single nucleotide polymorphisms (SNP) of different genes including interleukin 1A (IL-1A), interleukin 1B (IL-1B), interleukin 1 receptor antagonist (IL-1RN) [17, 18], and methylentetrahydrofolate reductase (MTHFR) [19, 20]. This evidence concerns the gene IL1RN and Alzheimer disease.