THRA and hypothyroidism: In mouse pups, deletion of THR-α and pharmacological hypothyroidism were both associated with downregulation of key genes in the control of proliferation and differentiation pathways in the small intestines, such as Cyclin D1, β-Catenin, and Cdx1 and Cdx2 homeobox genes (Fraichard et al., 1997; Plateroti et al., 1999, 2001; 2006).