U01.01.068 Vitamin B6

Vitamin B6, also called pyridoxine, is a vital water-soluble vitamin involved in numerous biochemical processes. Understanding its role, functions, and deficiency symptoms is critical for the USMLE Step 1.

Functions

Vitamin B6 is converted into its active form, pyridoxal phosphate (PLP), which serves as a cofactor for various enzymatic reactions:

Transamination Reactions
- Involved in amino acid metabolism (e.g., ALT and AST enzymes).
Decarboxylation Reactions
- Necessary for neurotransmitter synthesis.
Metabolic Pathways
- Glycogen Phosphorylase: Key role in glycogenolysis.
- Synthesis:
  - Glutathione: Antioxidant defense.
  - Cystathionine: Involved in methionine metabolism.
  - Heme: Critical for hemoglobin formation.
  - Niacin: Cofactor for NAD+ synthesis.
  - Histamine: Important for immune responses.
  - Neurotransmitters: Serotonin, epinephrine, norepinephrine, dopamine, and GABA.

Deficiency

Vitamin B6 deficiency can lead to significant clinical symptoms:

Symptoms	Pathophysiology/Notes
Convulsions	Impaired neurotransmitter synthesis (e.g., GABA).
Hyperirritability	Affected nervous system functions.
Peripheral Neuropathy	Can be induced by isoniazid or oral contraceptives.
Sideroblastic Anemia	Due to impaired heme synthesis, leading to iron accumulation.

Key Points to Remember

Active Form: Pyridoxal phosphate (PLP).
Associated Enzymes: ALT, AST, glycogen phosphorylase.
Clinical Relevance: Watch for deficiency in patients on isoniazid or oral contraceptives.
Mnemonic for Deficiency: “CHePS” (Convulsions, Hyperirritability, Peripheral neuropathy, Sideroblastic anemia).

USMLE Step 1 Review Series

Curriculum

U01.01.068 Vitamin B6

Functions

Deficiency

Key Points to Remember

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