Over the same postnatal time-frame, the numbers of proliferating cells in the intestinal epithelium were reduced in mouse models of congenital hypothyroidism (Pax8−/−, Flamant et al., 2002), deletion of the thyroid hormone receptor-α (THR-α−/−, Plateroti et al., 2006) and pharmacological thyroid hormone deficiency (propylthiouracil and low iodine, Plateroti et al., 2001). The gene discussed is PAX8; the disease is congenital hypothyroidism.