A 2-year-old male presents with failure to thrive and recurrent sinus infections. He is currently eating multiple and frequent meals a day and has met all of his developmental milestones. He has three sisters who have no past medical history and are meeting their growth developments. His caregiver is extremely concerned. They had to switch from cloth to disposable diapers because the cloth diapers were so difficult to clean. He just started toilet training, and his caregiver noticed a change in his bowel movements. A recessive genetic disease is suspected. Which of the following vitamin deficiencies is related to the most likely disease? A. Niacin B. Vitamin B12 C. Vitamin C D. Vitamin D