Snapshot A six-week-old male presents with lethargy and hypotonia. On physical exam, he is jaundiced and has a large protruding tongue. Introduction Insufficient iodine intake or defect in T4/thyroid formation leading to fetal hypothyroidism T4 is crucial during first two years of life for normal brain development Cretinism refers to untreated congenital hypothyroidism leads to congenital defects and physical abnormalities Presentation Symptoms severe mental retardation increased weight and short stature coarse facial features large protuding tounge umbilical hernia Evaluation Labs decreased T4 elevated TSH Treatment Treat with levothyroxine replacement Prognosis, Prevention, and Complications Prevention by newborn screening by law