A 28-year-old man with pancytopenia undergoes bone marrow examination. The marrow is hypocellular with no dysplastic changes and normal cytogenetics. Serum B12 and folate levels are normal. Which single feature best distinguishes acquired aplastic anemia from inherited bone marrow failure syndromes (e.g., Fanconi anemia) in this patient?

Explanation

## Distinguishing Acquired Aplastic Anemia from Inherited Bone Marrow Failure ### The Critical Discriminator: Chromosomal Fragility Testing **Key Point:** Chromosomal fragility testing using diepoxybutane (DEB) or mitomycin C (MMC) is the single best discriminator between acquired aplastic anemia and inherited bone marrow failure syndromes like Fanconi anemia. A positive test (increased chromosomal breaks) indicates an inherited syndrome; a negative test supports acquired aplastic anemia. ### Why This Matters Clinically **High-Yield:** Fanconi anemia and other inherited bone marrow failure syndromes carry: - Higher risk of malignant transformation (AML, solid tumors) - Different treatment implications (stem cell transplantation is contraindicated in some cases without prior conditioning; risk of secondary malignancies is elevated) - Genetic counseling and family screening requirements - Distinct prognosis and natural history Acquired aplastic anemia, by contrast, may respond to immunosuppressive therapy or supportive care alone. ### Comparative Diagnostic Approach | Feature | Acquired Aplastic Anemia | Inherited BM Failure (Fanconi) | |---------|--------------------------|--------------------------------| | **DEB/MMC test** | **Negative** (normal breaks) | **Positive** (↑ chromosomal breaks) | | **Age of onset** | Any age (often 20–40 yrs) | Often childhood to early adulthood | | **Family history** | Absent | May be present (autosomal recessive) | | **Bone marrow cellularity** | Hypocellular | Hypocellular | | **Morphology** | Normal | Normal | | **Cytogenetics** | Normal | Normal (unless secondary changes) | | **Associated features** | Seronegative hepatitis, drug exposure | Skeletal abnormalities, short stature, microcephaly (variable) | | **Response to IST** | Good in ~70% | Poor; higher malignancy risk | ### Mnemonic: DEB/MMC = DETECT Inherited Defects **D**iepoxybutane or **M**itomycin **C** testing **E**xposure to DNA cross-linking agents **T**ests for chromosomal fragility **E**ssential for distinguishing inherited from acquired **C**ritical before stem cell transplant decision **T**ransformation risk is higher in inherited forms ### Clinical Pearl All patients with pancytopenia and hypocellular marrow should undergo DEB/MMC testing before committing to a treatment plan, especially if stem cell transplantation is being considered. A positive test changes management strategy and prognosis counseling dramatically. [cite:Harrison 21e Ch 110; Robbins 10e Ch 14]