It is disease of infants, called cretinism. It is characterized by decreased BMR (50% than normal); stunted growth; retarded mental development so low I.Q., delayed puberty; decreased body temperature, heart rate, pulse rate, blood pressure and cardiac output; reduced urine output; decreased sugar level in blood, pigeon's chest (chest bulging forward in sternal region). Cretinism can be congenital (absence of thyroid due to genetic defect) or endemic (absence of iodine in diet). It can be corrected by thyroxin administration. The retarded mental and physical development associated with the hyposecretion of thyroid hormones.