Considering the hypothyroidism phenotype present only in Nkx2‐1−/− or Pax8−/− or double Nkx2‐1+/−Pax8+/− mice, we decided to study directly the knock‐out mice (Kimura et al, 1996; Mansouri et al, 1998; Amendola et al, 2005). Here, PAX8 is linked to hypothyroidism.