USMLE Step 1 Quiz: Vitamins Cofactors And Nutrition

A 28-year-old woman presents with a 2-month history of persistent headaches, nausea, and blurred vision. She has been taking high-dose over-the-counter supplements, including one for her acne. On examination, she is afebrile with normal vital signs. Funduscopic examination reveals papilledema. Her skin is dry and scaly, and she has mild hepatomegaly.

The patient's signs and symptoms are most likely due to toxicity from which of the following vitamins?

A 2-year-old child, exclusively breastfed and with limited sun exposure due to living in a northern city, is brought to the clinic for well-child checkup. The physician notes bowing of the legs (genu varum) and widening of the wrists. An X-ray confirms rachitic changes in the long bones.

Which of the following sets of laboratory findings is most likely to be found in this patient?

A 3-day-old infant, born at home via an unattended delivery, is brought to the emergency department for evaluation of persistent oozing from the umbilical stump and scattered bruises on his trunk and extremities. He did not receive any prophylactic medications after birth. Laboratory studies show a markedly prolonged prothrombin time (PT).

This infant's condition is due to a deficiency of a vitamin that serves as an essential cofactor for the post-translational modification of which of the following?

A 16-year-old boy with cystic fibrosis presents with progressive difficulty walking, poor balance, and decreased sensation in his legs. Neurologic examination reveals ataxia, diminished deep tendon reflexes, and loss of proprioception. A peripheral blood smear shows normocytic anemia with acanthocytes (spur cells).

A deficiency of which of the following vitamins is the most likely cause of this patient's neurologic and hematologic findings?

A 58-year-old man who is homeless and consumes large quantities of alcohol presents with a 4-month history of a rough, hyperpigmented rash in a symmetric distribution on sun-exposed areas of his arms and neck. He also reports chronic diarrhea and seems confused during the interview. His diet consists primarily of corn-based products.

This patient's constellation of symptoms is caused by a deficiency of a vitamin that is a precursor for which of the following coenzymes?

A 50-year-old man is being treated for active pulmonary tuberculosis with a standard multi-drug regimen that includes isoniazid. After several weeks of therapy, he develops tingling and burning sensations in his hands and feet. Laboratory studies show a microcytic anemia, and a bone marrow biopsy reveals ringed sideroblasts.

The medication is interfering with the function of a vitamin that is a required cofactor for the first step in the synthesis of which of the following molecules?

A 24-year-old woman is in her 8th week of gestation. Her medical history is significant for a seizure disorder, for which she takes phenytoin. She is concerned about the health of her fetus. Her obstetrician stresses the importance of prenatal vitamin supplementation to decrease the risk of a specific class of birth defects.

Supplementation with folate is critical in this patient to prevent neural tube defects by providing methyl groups for the synthesis of which of the following?

A 35-year-old man who is a competitive bodybuilder presents with a 3-month history of a scaly rash around his eyes, nose, and mouth, as well as significant hair loss and muscle aches. He reports consuming a dozen raw egg whites daily as part of his high-protein diet. Laboratory tests are otherwise unremarkable.

The patient's symptoms are most likely caused by a deficiency of a vitamin that acts as a prosthetic group for which class of enzymes?

An 11-year-old boy with a history of Crohn disease presents with poor growth, delayed onset of puberty, and a vesiculobullous rash around his mouth and on his buttocks. He also complains of altered taste sensation and has had several minor infections with poor wound healing over the past year.

A deficiency of which of the following trace elements best explains this patient's constellation of findings?

A 29-year-old woman presents to her primary care physician with complaints of fatigue, weakness, and feeling cold all the time. She also notes occasional cravings for ice chips. She has a history of heavy menstrual periods. Physical examination reveals pale conjunctivae and spoon-shaped nails (koilonychia). A CBC shows microcytic, hypochromic anemia.

This patient's condition is due to a deficiency of a mineral that is essential for the function of which of the following proteins?

A 52-year-old woman who underwent Roux-en-Y gastric bypass surgery four years ago presents with numbness and tingling in her extremities and a spastic gait. Laboratory studies reveal a microcytic anemia that has been unresponsive to oral iron supplementation. Further testing shows low serum levels of ceruloplasmin.

A deficiency of which of the following trace elements is the most likely cause of her neurologic and hematologic findings?

A 38-year-old woman who recently immigrated from a remote, inland mountainous region of Southeast Asia presents with a visibly enlarged thyroid gland. She also complains of chronic fatigue, a 10-lb weight gain over the past year despite a poor appetite, and persistent constipation. On examination, a diffuse, non-tender goiter is palpated.

This patient's condition is most likely caused by a deficiency of a mineral required for the organification process, which involves its covalent binding to which of the following?

A 45-year-old man has been receiving total parenteral nutrition (TPN) for the past 6 months following extensive small bowel resection. He develops progressive shortness of breath and lower extremity edema. An echocardiogram reveals a dilated cardiomyopathy with a significantly reduced ejection fraction. The TPN formulation is found to be deficient in certain trace elements.

A deficiency of which of the following trace minerals is the most likely cause of this patient's cardiomyopathy?

A 72-year-old man with chronic kidney disease presents with bone pain and muscle weakness. Laboratory results show hypocalcemia, hyperphosphatemia, and a markedly elevated parathyroid hormone level. He is diagnosed with renal osteodystrophy.

The pathogenesis of this condition is primarily related to the failure of the kidney to synthesize the active form of Vitamin D, which involves which specific enzymatic step?

A 39-year-old woman with a history of severe alcoholism and malnutrition presents with deep cracks and fissures at the corners of her mouth and a painful, smooth, magenta-colored tongue. She also complains of greasy, scaling dermatitis in the nasolabial folds. An eye examination reveals corneal vascularization.

This patient's symptoms are characteristic of a deficiency of a vitamin that serves as a precursor for cofactors required by which of the following enzymes?

A 62-year-old man with a long history of alcohol abuse is brought to the emergency department due to confusion, unsteady gait, and abnormal eye movements. Upon arrival, he is given an intravenous infusion of 5% dextrose in normal saline. Shortly after, his confusion worsens, and he becomes lethargic.

The patient's decompensation after glucose administration is due to an increased requirement for a vitamin cofactor essential for the function of which of the following enzymes?

A 70-year-old man is started on warfarin for atrial fibrillation. He is counseled to avoid large variations in his intake of foods such as kale, spinach, and broccoli. The anticoagulant effect of warfarin can be overcome by high intake of the vitamin found in these foods.

Warfarin exerts its therapeutic effect by inhibiting an enzyme that is required for the regeneration of the active form of this vitamin. The vitamin itself is a cofactor for which of the following enzymes?

A 4-year-old boy, recently immigrated from a refugee camp, is brought to the pediatrician due to difficulty seeing in the evening and frequent stumbling in dimly lit rooms. His mother also notes that his eyes appear unusually dry. On physical examination, conjunctival xerosis and small, gray, foamy plaques on the bulbar conjunctiva are noted. The child's diet in the camp consisted mainly of rice.

This patient's condition is caused by a deficiency of a vitamin that is essential for which of the following processes?

An 80-year-old man who lives alone is brought to his physician by his daughter due to concerns about his health. He appears malnourished. Physical examination reveals swollen, bleeding gums, numerous small hemorrhages around hair follicles on his legs, and several large bruises. A small cut on his arm from a week ago has not healed properly. His diet consists mainly of tea and toast.

This patient's clinical findings are due to the impaired function of an enzyme responsible for which of the following biochemical processes?

A 70-year-old woman with a history of pernicious anemia presents with progressive fatigue, paresthesias in her lower extremities, and difficulty with balance. Her complete blood count reveals a hemoglobin of 9.2 g/dL and a mean corpuscular volume of 115 fL. Neurologic examination confirms loss of vibratory and position sense in the legs.

The neurologic dysfunction in this patient is primarily attributed to the impaired function of an enzyme that requires this vitamin to convert methylmalonyl-CoA into which of the following substances?