DIO1 and hyperthyroidism: This resulted in elevated serum T3 levels, lower serum T4 and completely suppressed hypophyseal thyroid-stimulating hormone β (Tshb) mRNA expression in treated dams (Fig. 1b), indicative of hyperthyroidism, which was confirmed by elevated gene expression of hepatic deiodinase type I (Dio1) and thyroid hormone inducible hepatic protein (Thrsp) as well as increased liver and heart weight (Supplementary Fig. 1a, b).