Among non-HLA genes, CTLA4 and PTPN22 were most consistently identified as predisposing to both HT and GD (121–124), while the TSHR locus appears to be specific for GD, but not HT, suggesting some genetic differences between these two types of AITD (125, 126); however, similar to PCOS, candidate gene screening for HT susceptibility mainly generated controversial and non-replicable findings (127–132). Here, CTLA4 is linked to hematocrit.