Iodine deficiency

A 20-day-old male newborn is brought to the pediatrician due to poor feeding for the past several weeks. The mother had minimal prenatal care and delivered the baby at home. She had no complications during the pregnancy and took daily prenatal vitamins. The patient is at the 95th percentile for head circumference, 45th percentile for length and 50th percentile for weight. Vital signs are within normal limits. Physical examination reveals a mildly enlarged mass on the neck that is nontender to palpation. There is mild scleral icterus and yellowing of the skin. Fundoscopic examination of the eyes reveals no abnormalities. The tongue is enlarged and protruding from the mouth. The abdomen is mildly distended, with a reducible, soft protruding mass at the umbilicus. Which of the following is the most likely cause of this patient’s condition?