You are answering a USMLE-style medical question. Question: A 10-year-old boy is brought to the emergency room by his grandparents. He is in a wheelchair with soft restraints because he has been violent and had been trying to hurt himself that day. The child’s parents died in a car accident 1 month ago. His grandparents also brought the medications he stopped taking after his parents’ death, including multivitamins, allopurinol, and diazepam. They say that their grandson has been using these medications for many years; however, they are unable to provide any medical history and claim that their grandson has been behaving strangely, exhibiting facial grimacing, irregular involuntary contractions, and writhing movements for the past few days. They also note that he has had no teeth since the time they first met him at the age of 2. An intramuscular medication is administered to calm the boy down prior to drawing blood from him for laboratory tests. Which of the following biochemical pathway abnormalities is the most likely cause of this patient’s condition? Options: A) Hypoxanthine-guanine phosphoribosyl transferase of the pyrimidine metabolism pathway B) Aminolevulinic acid synthetase of the heme metabolism pathway C) Hypoxanthine-guanine phosphoribosyl transferase of the purine metabolism pathway D) Thymidylate synthetase of the pyrimidine metabolism pathway Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.