Q. A 5-year-old boy is seen at a pediatric clinic with complaints of decreased appetite and recurrent diarrheal episodes over the past 6 months. On examination, the boy exhibits sparse hair, a dry, scaly rash on his face, hands, and lower extremities, and has a significantly low weight for his age. His mother mentions he has had recurrent skin infections, and his wounds seem to take longer to heal. The mother also mentions that he has difficulty tasting foods and often complains of mouth discomfort. The boy has no known allergies and his vaccinations are up to date. Based on the clinical presentation, which nutrient deficiency is most likely to be the cause of this patient's symptoms?