Cretinism, deficiency disease caused by congenital absence of thyroxine, a hormone secreted by the thyroid gland, and characterized by defective mental and physical development. Cretins have dwarfed bodies, with curvature of the spine and pendulous abdomen. Their limbs are distorted, their features are coarse, and their hair is harsh and scanty. Mental development is retarded throughout life. An adult cretin may reach the intelligence of only a four-year-old child. Research has revealed that when an animal or human infant is born with a deficiency of thyroxine, the neurons (nerve cells) in the brain do not develop the multiple branches that normally form the brain's complex network. Treatment of adult cretins with thyroxine or thyroid extract results in some improvement; early treatment in infancy results in cure of the disease and normal development of the individual, provided the treatment is continued throughout life. Treatment is sometimes begun prenatally, for instance, when a mother suffers from severe goiter, a disease of the thyroid.
Endemic cretinism is found associated with goiter throughout the world, especially in certain valleys of the Alps and Pyrenees Mountains, and in Syria, India, and China. Families moving into such areas tend to develop goiter in the first generation and cretinism in the second and succeeding generations. Public health measures, including the addition of iodine to public water supplies, have proved beneficial in reducing the incidence of goiter and cretinism in certain areas. Iodine is an essential building block of thyroxine. See also Hormone; Myxedema.