Vitamin B7 deficiency

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Background

  • Almost all food contain significant quantities of biotin, but it is most found in plants, liver, egg yolk, soybean products, and yeast.
  • Daily biotin requirement is low (150-300 ug/d).
  • Intestinal flora synthesizes significant quantities of biotin.
  • Biotin is recycled in the body and eventually lost in urine and feces.
  • Biotin (Vitamin B7) is a cofactor in four major carboxylation reactions
  1. Acetyl-CoA Carboxylase (ACC) - Acetyl-CoA to Malonyl-CoA in Fatty Acid Synthesis
  2. Pyruvate Carboxylase (PC) - Pyruvate to Oxaloacetate in Gluconeogenesis
  3. Propinoyl-CoA Carboxylase (PCC) - Propinoyl-CoA to Methylmalonyl-CoA in Odd Chain Fatty Acid Metabolism
  4. Methylcrotonyl CoA Carboxylase (MCC) - 3-Methylcrotonyl CoA to 3-Methylglutaconyl CoA in Leucine Metabolism
  • Biotin deficiency is relatively rare. Populations at risk:
  1. Long-term Parenteral Nutrition
  2. Consumption of raw egg whites (bodybuilders or boxers)
  • Secondary biotin deficiency (Multiple Carboxylase Deficiency) is caused by two inherited defects in metabolism:
  1. Holocarboxylase Synthetase Deficiency - Autosomal Recessive disorder. Holocarboxylase Synthetase is required to attach biotin to other molecules. Deficiency in this enzyme prevents cells from using Biotin.
  2. Biotinidase Deficiency - Biotinidase is required to release Biotin that is bounded to protein.

Clinical Features

  • Classical Presentation:
    • Dermatitis - specifically around eyes, nose, mouth
    • Alopecia
    • Enteritis
    • Neurological - including AMS, lethargy, hallucinations, paresthesias
  • Holocarboxylase Synthetase Deficiency - presents in the first week of life with:
    • lethargy
    • hypotonia
    • vomiting
  • Biotinidase Deficiency - presents later in life with:
    • dermatitis
    • neurological symptoms - ataxia, seizures, myoclonus, nystagmus
    • ketoacidosis

Differential Diagnosis

  • DDx involves genetic disorders with impaired carboxylation.
    • Biotinidase Deficiency (see above)
    • Holocarboxylase Synthetase Deficiency (see above)
    • Carnitine Deficiency
    • Methylmalonic Acidemia
    • Propionic Acidemia
    • Pyruvate Carboxylase Deficiency
  • Starvation
  • Medication Use - Antibiotics or Anti-convulsants
  • Other vitamin deficiencies:

Vitamin deficiencies

Evaluation

  • Diagnosis is primarily clinical. Routine serum chemistry panel should be checked.
  • Other Laboratory Studies
    • Newborn Screening
    • Serum Biotinidase Activity decreased
    • Serum Ammonia Levels increased
    • Plasma Carnitine
    • Quantitative Amino Acid levels
    • Urine B-Hydroxyisoverlate decreased
    • Urine Biotin decreased
    • Urine Ketones increased

Management

  • Supplementation of Biotin. Dosage is debated:
    • 150 ug intramuscular injection suggested
    • 5-20 mg/dl have also been used
  • Stop consumption of raw eggs.
  • Stop anti-convulsant or anti-biotic use.

Disposition

  • Follow-up with primary care provider or referral to genetic specialist.

See Also

External Links

References

Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline, 1998. Mock D. Biotin. In: Modern Nutrition in Health and Disease, 9th, Shils M (Ed), Lippincott Williams and Wilkins, Philadelphia 2000. p.459.