In 2013 Jian Zhang et al. identified and confirmed a higher prevalence of A alleles of IL-21 rs2221903 SNP in Graves’ disease patients and also for the IL-21R gene, compared with controls, the genotype frequencies of rs3093301 and rs2285452 were significantly different in Hashimoto’s thyroiditis (HT) patients. The gene discussed is IL21; the disease is hematocrit.