Cause: Deficiency of Vitamin B₁ (Thiamine) . Biochemical Role: Thiamine is a coenzyme for pyruvate dehydrogenase, α‑ketoglutarate dehydrogenase, and transketolase – essential in carbohydrate metabolism. Types & Symptoms: Dry Beri-Beri: Peripheral neuropathy, muscle weakness. Wet Beri-Beri: Cardiomegaly, tachycardia, edema, high-output cardiac failure. Real Data: In severe deficiency, erythrocyte transketolase activity decreases; normal activity is 42–86 μmol/min/L, but can drop below 25 μmol/min/L in Beri-Beri.