Previously, genetic linkage analysis and candidate gene association studies in osteosarcoma have implicated several loci and candidate genes, for example, several study showed that the X-ray repair cross-complementing group-1 (XRCC1),[10] excision repair cross-complementation (ERCC),[10,11] 5,10-methylenetrahydrofolate reductase (MTHFR),[12] insulin-like growth factor 1 (IGF-1),[13] the apurinic/apyrimidinic endonuclease (APE1),[14] and tumor suppressor gene TP53[15] were associated with susceptibility to osteosarcoma. The gene discussed is MTHFR; the disease is osteosarcoma.