CAD: cervical artery dissection; TIA: transient ischemic attack; IS: ischemic stroke; MTHFR: methylenetetrahydrofolate reductase; SVD: small vessel disease; GWAS: Genome-wide Association Study; Met-B12: methyle-B12; VAD: vetebral artery dissection; HHCY: hyperhomocysteinemia; HCY: homocysteine; FA: folic acid; 5-Me-THF: 5-methyltetrahydrofolate. The gene discussed is MTHFR; the disease is hyperhomocysteinemia.