Protein Y is a type of protein that is distributed in the liver and promotes the absorption of thyroid hormones by the liver; the decrease of protein Y makes the liver speed up the circulation of thyroid hormones and reduce the free thyroid hormones in the blood (Reyes et al., 1971), leading to hypothalamus–pituitary–thyroid disorders, increase in TSH, and appearance of symptoms of hypothyroidism. The gene discussed is TG; the disease is hypothyroidism.