A 34-year-old man comes to the physician because of palpitations, shortness of breath, diarrhea, and abdominal cramps for 2 months. Physical examination shows cutaneous flushing of the face. Auscultation of the chest shows bilateral wheezing. A 24-hour urine collection shows increased 5-hydroxyindoleacetic acid (5-HIAA) concentration. A contrast-enhanced CT scan of the abdomen shows an intestinal tumor with extensive metastasis to the liver. A diagnosis of an inoperable disease is made and the patient is started on treatment with octreotide. Six weeks later, the patient's symptoms have improved except for his abdominal pain and frequent loose stools. The physician suggests enrolling the patient in a trial to test additional treatment with a new drug that has been shown to improve symptoms in other patients with the same condition. The expected beneficial effect of this new drug is most likely caused by inhibition of which of the following?
AHistidine decarboxylase
BPlasma kallikrein
CVasoactive intestinal peptide
DTryptophan hydroxylase
EDopamine β-hydroxylase
You are examining a 3-day-old newborn who was delivered vaginally without any complications. The newborn presents with vomiting, hyperventilation, lethargy, and seizures. Blood work demonstrates hyperammonemia, elevated glutamine levels, and decreased blood urea nitrogen. A CT scan demonstrates cerebral edema. Defects in which of the following enzymes would result in a clinical presentation similar to this infant?
ACarbamoyl phosphate synthetase I
BHomogentisate oxidase
CCystathionine synthase
DBranched-chain ketoacid dehydrogenase
EPhenylalanine hydroxylase
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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