A 52-year-old man is being evaluated in the emergency department for abdominal pain associated with watery diarrhea. His symptoms have been progressive over the last month. He says that he is depressed and often has difficulty remembering things. The patient has a 20-year history of alcohol use disorder. On examination, he appears disheveled. A pigmented scaly skin rash is present in the malar distribution of his face, neck, and back of his hands. The rash has been present for several months and worsens on exposure to sunlight. It is determined that the patient's symptoms are secondary to lack of a specific nutrient. Activity of which of the following enzymes is most likely decreased in the patient as a result of this deficiency?

Question

A 52-year-old man is being evaluated in the emergency department for abdominal pain associated with watery diarrhea.  His symptoms have been progressive over the last month.  He says that he is depressed and often has difficulty remembering things.  The patient has a 20-year history of alcohol use disorder.  On examination, he appears disheveled.  A pigmented scaly skin rash is present in the malar distribution of his face, neck, and back of his hands.  The rash has been present for several months and worsens on exposure to sunlight.  It is determined that the patient's symptoms are secondary to lack of a specific nutrient.  Activity of which of the following enzymes is most likely decreased in the patient as a result of this deficiency?

Quizplus · Accepted Answer

11ec160b_36b4_9c0a_9249_932ac60d3d69_MD0001_00 This patient likely has pellagra, a disease characterized by photosensitive dermatitis, diarrhea, and dementia occurring secondary to vitamin B₃ (niacin) deficiency. In the United States, pellagra is seen predominantly in malnourished populations (eg, patients with alcohol use disorder or GI malabsorption). Niacin is a precursor for nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), two important cofactors for many dehydrogenase and reductase enzymes. NAD is required for catabolic reactions (eg, glycolysis, beta-oxidation) as well as cell signaling and DNA repair, whereas NADP is necessary for many anabolic reactions such as fatty acid and cholesterol synthesis. NAD is a key constituent of the citric acid cycle; it serves as a cofactor for isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase. (Choice A) Citrate synthase is an enzyme of the citric acid cycle; it does not require NAD or NADP as a cofactor. (Choices B and D) Hexokinase and phosphoglycerate kinase are enzymes used in glycolysis; they do not require NAD or NADP as cofactors. (Choice E) Succinate dehydrogenase is an enzyme of the citric acid cycle; it catalyzes the conversion of succinate to fumarate using flavin adenine dinucleotide (FAD) as a cofactor. Educational objective: Niacin is a precursor for nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), two important cofactors for many dehydrogenase and reductase enzymes. Niacin deficiency results in pellagra (ie, diarrhea, dementia, and dermatitis). __________ References: Pellagra: a non-eradicated old disease. (http://www.ncbi.nlm.nih.gov/pubmed/24847436)

A 52-Year-Old Man Is Being Evaluated in the Emergency Department