Review Question - QID 214528

An 18-month-old boy is brought into the office by his parents for abnormal behavior. For the past month, he has been banging his head on the wall, scratching himself, and biting his tongue. He has also had difficulty achieving motor developmental milestones. He could not sit unsupported until 8 months of age and only recently began walking. When he does walk, he often falls and bumps into objects. The patient was adopted and the parents are unsure of his prenatal or family history. The patient’s temperature is 98.6°F (37°C), blood pressure is 90/56 mmHg, pulse is 80/min, and respirations are 15/min. On physical examination, the patient is nonverbal. There is spasticity and hyperreflexia throughout the upper and lower extremities bilaterally. Several abrasions are noted on his arms and tongue. Which of the following is the most likely cause of this patient’s condition?