Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 7)

BiotinBiotin is a water-soluble vitamin that plays a role in gene expression, gluconeogenesis, and fatty acid synthesis and serves as a CO 2 carrier on the surface of both cytosolic and mitochondrial carboxylase enzymes. The vitamin also functions in the catabolism of specific amino acids (e.g., leucine). Excellent food sources of biotin include organ meat such as liver or kidney, soy, beans, yeast, and egg yolks; however, egg white contains the protein avidin, which strongly binds the vitamin and reduces its bioavailability.Biotin deficiency due to low dietary intake is rare; rather, deficiency is due to inborn errors of metabolism....
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Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 7) Chapter 071. Vitamin and Trace Mineral Deficiency and Excess (Part 7) Biotin Biotin is a water-soluble vitamin that plays a role in gene expression,gluconeogenesis, and fatty acid synthesis and serves as a CO 2 carrier on thesurface of both cytosolic and mitochondrial carboxylase enzymes. The vitaminalso functions in the catabolism of specific amino acids (e.g., leucine). Excellentfood sources of biotin include organ meat such as liver or kidney, soy, beans,yeast, and egg yolks; however, egg white contains the protein avidin, whichstrongly binds the vitamin and reduces its bioavailability. Biotin deficiency due to low dietary intake is rare; rather, deficiency is dueto inborn errors of metabolism. Biotin deficiency has been induced byexperimental feeding of egg white diets and in patients with short bowels whoreceived biotin-free parenteral nutrition. In the adult, biotin deficiency results inmental changes (depression, hallucinations), paresthesia, anorexia, and nausea. Ascaling, seborrheic, and erythematous rash may occur around the eyes, nose, andmouth as well as on the extremities. In infants, biotin deficiency presents as hypotonia, lethargy, and apathy. Inaddition, the infant may develop alopecia and a characteristic rash that includesthe ears. The laboratory diagnosis of biotin deficiency can be established based on adecreased urinary concentration or an increased urinary excretion of 3-hydroxyisovaleric acid after a leucine challenge. Treatment requirespharmacologic doses of biotin, using up to 10 mg/d. No toxicity is known. Pantothenic Acid (Vitamin B5) Pantothenic acid is a component of coenzyme A and phosphopantetheine,which are involved in fatty acid metabolism and the synthesis of cholesterol,steroid hormones, and all compounds formed from isoprenoid units. In addition, pantothenic acid is involved in the acetylation of proteins. Thevitamin is excreted in the urine, and the laboratory diagnosis of deficiency is madeon the basis of low urinary vitamin levels. The vitamin is ubiquitous in the food supply. Liver, yeast, egg yolks, wholegrains, and vegetables are particularly good sources. Human pantothenic aciddeficiency has been demonstrated only in experimental feeding of diets low inpantothenic acid or by giving a specific pantothenic acid antagonist. The symptoms of pantothenic acid deficiency are nonspecific and includegastrointestinal disturbance, depression, muscle cramps, paresthesia, ataxia, andhypoglycemia. Pantothenic acid deficiency is believed to have caused the burningfeet syndrome seen in prisoners of war during World War II. No toxicity of thisvitamin has been reported. Choline Choline is a precursor for acetylcholine, phospholipids, and betaine.Choline is necessary for the structural integrity of cell membranes, cholinergicneurotransmission, lipid and cholesterol metabolism, methyl-group metabolism,and transmembrane signaling. Recently, a recommended adequate intake was set at 550 mg/d for adultmales and 425 mg/d for adult females, although certain genetic polymorphismscan increase an individuals requirement for choline. Choline is thought to be aconditionally essential nutrient, in that de novo synthesis occurs in the liver andis less than the vitamins utilization only under certain stress conditions (e.g.,alcoholic liver disease). The dietary requirement of choline depends on the status of other methyl-group donors (folate, vitamin B12, and methionine) and thus varies widely. Cholineis widely distributed in food (e.g., egg yolk, wheat germ, organ meat, milk) in theform of lecithin (phosphatidylcholine). Choline deficiency has occurred in patients receiving parenteral nutritiondevoid of choline. Deficiency results in fatty liver, elevated transaminase levels,and skeletal muscle damage with high creatine phosphokinase values. The diagnosis of choline deficiency is currently made on the basis of lowplasma levels, although nonspecific conditions (e.g., heavy exercise) may suppressplasma levels. Toxicity from choline results in hypotension, cholinergic sweating,diarrhea, salivation, and a fishy body odor. The upper limit for choline has beenset at 3.5 g/d. Therapeutically, choline has been suggested for patients with dementia andfor patients at high risk of cardiovascular disease, due to its ability to lowercholesterol and homocysteine levels. However, such benefits have yet to bedocumented. Choline- and betaine-restricted diets are of therapeutic value intrimethylaminuria (fish odor syndrome).