Since the identification of the first causal gene for thyroid dysgenesis PAX8 in 1998 [18], a number of genes underlying congenital primary hypothyroidism (CH) have been reported to play a role in this phenotype (e.g., TSHR, NKX2-1, NKX2-5, FOXE1, GLIS3, JAG1, TBX1, NTN1, CDCA8, HOXD3, HOXB3, CDCH8, TUBB1, and TRPC4AP) [5,19,20]. This evidence concerns the gene JAG1 and cyclic hematopoiesis.