An 8-day-old boy is brought to the physician by his mother because of vomiting and poor feeding. The pregnancy was uncomplicated, and he was born at full term. He appears pale and lethargic. Physical examination shows diffusely increased muscle tone. His urine is noted to have a sweet odor. This patient's symptoms are most likely caused by the accumulation of which of the following?
APhenylalanine
BHomogentisic acid
CIsoleucine
DHomocysteine
EPhytanic acid
A 36-year-old woman comes to the physician because of prolonged stiffness in the morning and progressive pain and swelling of her wrists and hands over the past 4 months. Examination shows bilateral swelling and mild tenderness of the wrists and the second, third, and fourth metacarpophalangeal joints. Her range of motion is limited by pain. Serum studies show elevated anti-cyclic citrullinated peptide antibodies. Treatment with methotrexate is begun. At a follow-up examination, her serum aspartate aminotransferase (AST) concentration is 75 U/L and her serum alanine aminotransferase (ALT) concentration is 81 U/L. Which of the following substances is essential for the function of these enzymes?
AThiamine
BPyridoxine
CFolic acid
DRiboflavin
ENiacin
A 30-year-old African American G1P0 mother gives birth to a male infant at 33 weeks' gestation. The mother had no prenatal care and took no prenatal vitamins. The child’s postnatal period was complicated by neonatal sepsis due to group B Streptococcus. He required a two week stay in the neonatal intensive care unit to receive antibiotics, cardiopulmonary support, and intravenous nutrition. He eventually recovered and was discharged. At a normal follow-up visit to the pediatrician’s office one month later, the mother asks about the child’s skin color and hair color. On examination, the child has white hair and diffusely pale skin. The child’s irises appear translucent. Further questioning of the mother reveals that there is a distant family history of blindness. This child most likely has a defect in an enzyme involved in the metabolism of which of the following molecules?
ALeucine
BHomocysteine
CPhenylalanine
DHomogentisic acid
EDOPA
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