A 52-year-old woman comes to the office with a 2-month history of skin rash that worsens with sun exposure. Her family says that lately she has become irritable, hostile, and has had episodes of disorientation. The patient does not use tobacco or illicit drugs but has been drinking half a bottle of gin daily. Further questioning reveals poor nutritional intake and intermittent diarrhea. The patient restricts her diet for weight control. Body mass index is 17 kg/m². On examination, she has a well-demarcated, hyperpigmented, scaly rash on the hands, forearms, and upper chest. The cause of most of her symptoms is determined to be a lack of the precursor vitamin for synthesis of NAD⁺ coenzyme. The compensatory pathway to synthesize this coenzyme uses which of the following as a precursor?

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11ec160b_36d6_2e0d_9249_7dd657aca77b_MD0001_00 Pellagra ("rough skin" in Italian vernacular) is due to niacin deficiency and is characterized by the "3 Ds": dermatitis, diarrhea, and dementia: Niacin (nicotinic acid, or vitamin B₃) is an essential component of the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which participate in redox metabolism. Specifically, NAD functions as a coenzyme for dehydrogenases involved in the metabolism of fats, carbohydrates, and amino acids; NADP is crucial in the hexose-monophosphate shunt of glucose metabolism and for biosynthesis of cholesterol and fatty acids. Niacin can be obtained through dietary intake or synthesized endogenously from tryptophan. In developing countries, niacin deficiency is seen in populations that subsist primarily on corn products (niacin in corn occurs in a bound, unabsorbable form). In developed countries, it is primarily seen in patients with impaired nutritional intake (eg, alcohol use disorder, chronic illness). Pellagra can also be seen occasionally in those with carcinoid syndrome, prolonged isoniazid therapy, or Hartnup disease. (Choice A) Arginine is the precursor of nitric oxide, urea, ornithine, and agmatine. It is also necessary for the formation of creatine. (Choice B) Carotene is the precursor to vitamin A. (Choice C) Cholesterol is the precursor to steroid hormones. (Choice D) Orotic acid is a precursor of pyrimidine. (Choice E) Phenylalanine is the precursor to tyrosine, an amino acid necessary for the formation of catecholamines. Educational objective: Niacin (vitamin B₃) can be synthesized endogenously from tryptophan and is an essential component of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). A deficiency of this vitamin results in pellagra, which is characterized by dermatitis, diarrhea, and dementia. __________ References: Pellagra and alcoholism: a biochemical perspective. (http://www.ncbi.nlm.nih.gov/pubmed/24627570)

A 52-Year-Old Woman Comes to the Office with a 2-Month