While total serum T3 and T4 were surprisingly normal in the pregnant TRβ-/- dams as compared to TRβ+/- females, pituitary Tshb and Dio2 mRNA showed the expected upregulation due to the lack of TRβ mediated negative feedback loop (Fig. 4b), a hallmark of thyroid hormone resistance (RTH)31. This evidence concerns the gene TSHB and generalized resistance to thyroid hormone.