For exmaple, Sugisawa et al. conducted the mutation screening study covering five genes (IGSF1, IRS4, TBL1X, TRHR, and TSHB) in Japanese patients with central congenital hypothyroidism and identified the IGSF1 defect as the leading genetic cause in their patient cohort [42]. This evidence concerns the gene TBL1X and central congenital hypothyroidism.