A 28-year-old Indian male presents to the emergency department with severe hemolytic anemia following consumption of fava beans. Laboratory investigations reveal hemoglobin 7.2 g/dL, reticulocyte count 8%, elevated indirect bilirubin, and elevated LDH. Peripheral blood smear shows Heinz bodies. Urine dipstick is positive for blood but microscopy shows no RBCs. Which of the following enzyme deficiencies best explains this clinical presentation?

Explanation

## Clinical Diagnosis: G6PD Deficiency with Acute Hemolytic Crisis ### Pathophysiology of the Presentation This patient presents with the classic triad of **G6PD deficiency (glucose-6-phosphate dehydrogenase deficiency)**: 1. **Oxidative stress trigger**: Fava beans contain oxidative compounds (divicine, isouramil) that precipitate hemolysis in G6PD-deficient RBCs. 2. **Hemolytic anemia**: Hemoglobin 7.2 g/dL with elevated reticulocyte count (8%) indicates acute RBC destruction and compensatory bone marrow response. 3. **Heinz bodies**: Denatured hemoglobin precipitates visible on supravital staining—pathognomonic for G6PD deficiency. ### Role of the Pentose Phosphate Pathway **Key Point:** G6PD catalyzes the first committed step of the **oxidative phase** of the pentose phosphate pathway (PPP), converting glucose-6-phosphate to 6-phosphogluconolactone. $$\text{Glucose-6-phosphate} \xrightarrow{\text{G6PD}} \text{6-Phosphogluconolactone}$$ This reaction generates **NADPH**, the critical reducing cofactor for: - **Glutathione reductase**: Converts oxidized glutathione (GSSG) → reduced glutathione (GSH) - **Glutathione peroxidase**: Uses GSH to neutralize H₂O₂ and lipid peroxides **Without G6PD → No NADPH → No GSH regeneration → Oxidative stress → Hemolysis** ### Why Hemoglobinuria Without RBCuria? **Clinical Pearl:** Free hemoglobin (from intravascular hemolysis) is filtered by the glomerulus and detected on dipstick. However, intact RBCs are too large to pass the glomerular filter, hence the discordance between positive dipstick and absent RBCs on microscopy. ### High-Yield Biochemical Summary | Feature | G6PD Deficiency | |---------|------------------| | **PPP enzyme affected** | Glucose-6-phosphate dehydrogenase (oxidative phase) | | **Cofactor lost** | NADPH | | **Antioxidant defense compromised** | GSH regeneration | | **RBC vulnerability** | Susceptible to oxidative stress | | **Trigger agents** | Fava beans, sulfonamides, aspirin, antimalarials | | **Hemolysis pattern** | Acute intravascular (hemoglobinuria, elevated LDH, low haptoglobin) | | **Heinz bodies** | Present (denatured Hb precipitates) | ### Mechanism Diagram ```mermaid flowchart TD A[Glucose-6-phosphate]:::outcome --> B{G6PD present?}:::decision B -->|Yes| C[6-Phosphogluconolactone]:::action C --> D[NADPH generated]:::outcome D --> E[Glutathione reductase active]:::action E --> F[GSH regenerated]:::action F --> G[H₂O₂ neutralized]:::action G --> H[RBC protected from oxidative stress]:::outcome B -->|No - G6PD deficiency| I[No NADPH]:::urgent I --> J[No GSH regeneration]:::urgent J --> K[H₂O₂ accumulates]:::urgent K --> L[Hemoglobin denaturation]:::urgent L --> M[Heinz bodies form]:::outcome M --> N[Intravascular hemolysis]:::urgent N --> O[Hemoglobinuria + Anemia]:::outcome ``` ### Why This Is High-Yield for NEET PG **Mnemonic: FAVA (Fava beans trigger hemolysis in G6PD)** - **F**ava beans (classic trigger) - **A**cute hemolytic anemia (presentation) - **V**ulnerability to oxidative stress (mechanism) - **A**ntioxidant defense failure (biochemistry) G6PD deficiency is the **most common enzyme deficiency worldwide** (>400 million affected), with high prevalence in India, Africa, Mediterranean, and Southeast Asia. It is a **high-yield topic** in NEET PG because it bridges biochemistry (PPP), hematology (hemolysis), and clinical pharmacology (drug-induced hemolysis).