Myxoedema (Gulls disease) occurs due to the deficiency of thyroxine in adults, it causes low BMR (by 30-40\%), low body temperature, tendency to retain water in tissues, reduced heart rate, pulse rate, blood pressure and cardiac output, low sugar and iodine level in blood, muscular weakness and oedema (accumulation of interstilial fluid that causes the facial tissues to swell and look fluffy).
Decrease secretion of thyroxine hormone from thyroid gland causes hypothyroidism.
simple goitre is caused by lower intake of iodine through diet.
Cretinism occurs due to hyposecretion of thyroxine during the growth years or birth.