A 6-year-old boy is brought to your pediatric clinic by his parents who are concerned with his growth and development. They immigrated to the United States a few months ago from Tunisia. He has not been growing as he should compared to other children of his age. At school, he has learning disabilities. His reading skills are poor. His motor skills are inadequate. Other children make fun of him for having a ‘musty body odor’. His behavior becomes erratic when he eats certain foods like beef, pork, lamb, venison, salmon, trout and drinks diet sodas. There are some children in their extended family with similar disorders. On physical examination, the boy has blue eyes and blonde hair; microcephaly, hypertonia and hyperreflexia in all four limbs. When you heard that there are some children in their extended family with similar disorders, you wondered whether this is an inherited autosomal recessive disorder. Which of the following is an autosomal recessive disorder?
