U01.01.064 Vitamin B1

Vitamin B1, also known as thiamine, plays a crucial role as a cofactor in key enzymatic processes in the body. Mastery of its functions and associated conditions is vital for the USMLE Step 1 exam.

Key Functions of Vitamin B1

Vitamin B1 is converted to Thiamine Pyrophosphate (TPP), which acts as a cofactor for several important dehydrogenase enzyme reactions:

Enzyme Reactions Requiring TPP

Enzyme	Pathway	Function
Branched-chain ketoacid dehydrogenase	Branched-chain amino acid metabolism	Breaks down branched-chain amino acids
α-Ketoglutarate dehydrogenase	Tricarboxylic Acid (TCA) Cycle	Converts α-ketoglutarate to succinyl-CoA
Pyruvate dehydrogenase	Glycolysis to TCA Cycle	Links glycolysis to the TCA cycle
Transketolase	Hexose Monophosphate (HMP) Shunt	Facilitates ribose synthesis and NADPH production

Mnemonic to Remember: Be APT

Branched-chain ketoacid dehydrogenase
Alpha-ketoglutarate dehydrogenase
Pyruvate dehydrogenase
Transketolase

Clinical Correlations: Disorders of Vitamin B1 Deficiency

Condition	Presentation	Key Features
Wernicke Encephalopathy	Acute, life-threatening neurologic condition	Classic triad: confusion, ophthalmoplegia, ataxia
Korsakoff Syndrome	Chronic amnestic disorder (often due to chronic alcohol consumption)	Confabulation, personality changes, memory loss (permanent)
Wernicke-Korsakoff Syndrome	Combination of Wernicke encephalopathy and Korsakoff syndrome	Damage to medial dorsal nucleus of thalamus and mammillary bodies
Dry Beriberi	Neurological symptoms	Polyneuropathy, symmetric muscle wasting
Wet Beriberi	Cardiovascular involvement	High-output cardiac failure (dilated cardiomyopathy) and edema

Tips to Remember

Mnemonic for Vitamin B1:
- Spell “beriberi” as Ber1Ber1 to associate it with Vitamin B1.
Common Exam Clues:
- Chronic alcohol consumption with neurologic symptoms = Wernicke-Korsakoff Syndrome.
- Heart failure and edema = Wet Beriberi.
- Neuropathy and muscle wasting = Dry Beriberi.
Transketolase Test:
- Activity increases with the addition of thiamine in Vitamin B1 deficiency.

Points to Remember for USMLE Step 1

Vitamin B1 is essential for carbohydrate metabolism; deficiencies manifest in high-energy-demand systems (nervous and cardiovascular).
Look for clinical contexts such as alcoholism, malnutrition, or bariatric surgery.
Understanding the pathways and related conditions helps with integrated exam questions involving biochemistry, neurology, and pathology.

USMLE Step 1 Review Series

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