## Distinguishing Features of Type 1 vs Type 2 Diabetes ### Key Pathophysiologic Differences **Key Point:** Type 1 diabetes is an autoimmune disorder with pancreatic beta-cell destruction, while Type 2 is a metabolic disorder characterized by insulin resistance and relative insulin deficiency. ### Feature Comparison Table | Feature | Type 1 DM | Type 2 DM | |---------|-----------|----------| | **Autoimmune markers** | Present (anti-GAD, anti-IA2, anti-ZnT8) | Absent | | **Insulin requirement** | Mandatory from onset | Not required initially; develops over time | | **DKA at presentation** | Common (5–10% present with DKA) | Rare (HHS more common) | | **Obesity association** | Weak; normal BMI typical | Strong; 80–90% obese | | **Age of onset** | Typically < 30 years | Typically > 40 years (but increasing in youth) | | **Metabolic syndrome** | Not a feature | Core feature | | **C-peptide levels** | Low/absent | Normal or elevated (early) | ### Why Option 4 is Correct **High-Yield:** Strong association with obesity and metabolic syndrome is a hallmark of Type 2 diabetes, NOT Type 1. Type 1 patients are typically lean at diagnosis. This feature does NOT differentiate Type 1 from Type 2—rather, it is a defining characteristic of Type 2 alone. ### Clinical Correlation **Clinical Pearl:** A lean adolescent presenting with acute hyperglycemia, polyuria, and polydipsia with positive autoimmune markers has Type 1 DM. An obese 50-year-old with gradual symptom onset and metabolic syndrome features has Type 2 DM. **Mnemonic: AUTOIMMUNE TYPE 1** — **A**ntibodies present, **U**nderweight typical, **T**ypically young, **O**ften acute onset, **I**nsulin mandatory, **M**etabolic syndrome absent, **M**uscle/fat loss, **U**nrelated to obesity, **N**ormal C-peptide absent, **E**ventual complete beta-cell failure.
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