Thyroid hormones
The thyroid hormones function via a well-studied set of nuclear receptors, termed the thyroid hormone receptors. These receptors, together with corepressor molecules, bind DNA regions called thyroid hormone response elements (TREs) near genes. This receptor-corepressor-DNA complex can block gene transcription. Triiodothyronine (T3), which is the active form of thyroxine(T4), goes on to bind to receptors. The deiodinase catalyzed reaction removes an iodine atom from the 5' position of the outer aromatic ring of Thyroxine's (T4) structure. When triiodothyronine (T3) binds a receptor, it induces a conformational change in the receptor, displacing the corepressor from the complex. This leads to recruitment of coactivator proteins and RNA polymerase, activating transcription of the gene.
Maternal hypothyroidism
Maternal hypothyroidism is hypothyroidism in pregnant mothers. Even with appropriate treatment, it may pose risks not only to the mother, but also to the fetus. Thyroid hormones, T4 and TSH, diffuse across the placenta traveling from the mother to fetus for 10–12 weeks before the fetus’s own thyroid gland can begin synthesizing its own thyroid hormones. The mother continues to supply some T4 to the fetus even after he/she is able to synthesize his/her own. Infants with sporadic congenital hypothyroidism show T4 concentrations in the umbilical cord suggesting the mother is still providing 25-50 percent of T4. If these infants are not screened soon after birth for their hypothyroidism and treated, the infants can become permanently intellectually disabled, since they can’t meet their bodies demand for T4.