A 4-year-old boy is brought to the pediatrician by his mother because of a concern that he has been exhibiting self-injurious behavior. She states that for the past several weeks, he has been chewing on his lips and biting his fingers. They have attempted to redirect his behavior without success. He also has been complaining of pain in both knees and both ankles. Past medical history is significant for speech delay.
Deficiency of which of the following enzymes is most likely responsible for the patient's condition?
- A) Alpha-glucosidase
- B) Galactose-1-phosphate uridyltransferase
- C) Hypoxanthine-guanine phosphoribosyltransferase
- D) Muscle glycogen phosphorylase