Combined T4/TSH/TBG evaluation in Dutch neonates enables diagnosis of permanent central CH with an incidence of 1:21 000 newborns.33 The incidence in Japan has been found to be much lower (1:160 000); however, although ethnic differences could be contributing, subsequent studies suggest this may reflect a less sensitive Japanese screening approach.34, 35. This evidence concerns the gene CD4 and cyclic hematopoiesis.