Hyposecretion of TH: in adults can lead to myxedema. Symptoms include low metabolic rate, thick and/or dry skin, puffy eyes, feeling chilled, constipation, edema, mental sluggishness, lethargy. Lack of iodine decreases TH levels, which triggers increased TSH secretion, triggering thyroid to synthesize more and more unusable thyroglobulin. Thyroid enlarges, TH is critical for normal growth and brain development in early childhood. May be asymptomatic or present with weak cry, poor feeding, constipation or prolonged jaundice. TH replacement is crucial and is usually lifelong.