MTHFR and hyperhomocysteinemia: Among them, hyperhomocysteinemia was the most important factor associated with an increased risk of SCD (OR = 5.905, 95% CI 1.654 to 21.085, P = 0.006), followed by the MTHFR C677T genotype (TT vs. CT and CC, OR = 3.201, 95% CI 1.353 to 7.572, P = 0.008) and vitamin B12 deficiency (OR = 3.009, 95% CI 1.277 to 7.092, P = 0.012).