Insufficient production of thyroxine may lead to three conditions: goitre, cretinism and myxoedema. Simple goitre is the enlargement of the thyroid. Cretinism affects growing children. Major symptoms are dwarfism and mental retardation. Myxoedema is a condition during which the person becomes sluggish with swelling in face and hands.
Excess secretion of thyroxine cause exophthalmic goitre. Symptoms of this condition includes increased metabolism, rapid heartbeat and protruding eyes.