Biotin

Question 1

What is another name for Biotin?

Answer 1

Vitamin B7

Question 2

What populations are at risk for biotin deficiency?

Answer 2

• Low levels in infants, alcoholic, and pregnancy
• Treatment with antibiotics
• Patients on TPN

Question 3

Why should people with biotin deficiency not have raw egg whites?

Answer 3

• Raw egg whites = contain avidin
• Binds biotin
• Heat labile therefore cooking eggs denatures it and destroys biotin-binding property

Question 4

Is biotin deficiency common? What occurs with deficiency?

Answer 4

• Rare
• Activities of carboxylases decrease

Question 5

What are the two types of biotin inborn errors?

Answer 5

• Holocarbocylase synthetase deficiency
• Biotinidase deficiency

Question 6

What is holocarboxylase synthetase deficiency?

Answer 6

• Multiple carboxylase deficiency
• Results in decreased activity of all 4 biotin-containing carboxylases
• S/S = dermatitis, alopecia, severe ketoacidosis, seizures

Question 7

Explain biotinidase deficiency

Answer 7

• Unable to release free biotin from foods and to recover it from enzymes = functional deficiency
• S/S = seizures, ataxia, developmental delay, skin rash and hair loss

Question 8

What are the Biotin requirements?

Answer 8

• No RDA set
• Gut microbial synthesis
• Daily dietary intake estimated at 50-300 micrograms/day
• No UL set
• TPN patients = 60 micrograms/day recommended

Question 9

How can you determine biotin requirements?

Answer 9

• Blood/serum = not sensitive
• Clinical symptoms can occur even when plasma biotin normal
• Urine = biotin and metabolites
• 3-hydroxyisovalerate = measure of MCC activity
• Lymphocyte PCC activity (enzyme that requires biotin)
• Lymphocyte FA composition

Question 10

Renal reabsorption ____________ as intake _______________

Answer 10

Increases; decreases

Question 11

What are non-food sources of biotin?

Answer 11

• Synthesized by microflora in large intestine (can contribute to biotin status)
• Not sure of availability
• Urinary and fecal content of biotin > dietary intake
• BUT impairment of biotin recycling results in symptoms of deficiency

Question 12

What are the food sources of biotin and what form are they in?

Answer 12

• In almost all foods
• Relatively low content
• Not commonly used in fortified foods
• Available as free biotin and biotinyl-proteins/biocytin. Most of it bound to proteins, ratio of free to bound depends on food
• Protein bound = animal products, nuts, cereals
• Free = vegetables, green plants, fruits, milk

Question 13

How is biotin excreted?

Answer 13

• Renal reabsorption essential for biotin homeostasis and conservation
• Uptake is carrier-mediated and Na-dependent
• Most excretion = biotin
• Other metabolites/degradation products