## Analysis of Glycogen Storage Disorders ### Key Point: **GSD Type III does NOT have normal blood lactate levels.** Although Cori disease (debranching enzyme deficiency) is milder than Type I, it still causes elevated lactate because glucose-6-phosphate is shunted into glycolysis, producing lactate. The distinguishing feature of Type III is that lactate elevation is *less severe* than Type I, not absent. ### Correct Statements Reviewed | GSD Type | Enzyme Defect | Key Features | |----------|---------------|---------------| | **Type I (Von Gierke)** | Glucose-6-phosphatase | Severe fasting hypoglycemia, lactic acidosis, hepatomegaly, "doll-like" face | | **Type II (Pompe)** | Acid α-glucosidase (lysosomal) | Infantile: cardiomegaly, muscle weakness; Adult: slowly progressive myopathy | | **Type III (Cori)** | Debranching enzyme | Hepatomegaly, growth retardation, *elevated lactate* (though less than Type I) | | **Type V (McArdle)** | Muscle phosphorylase | Exercise intolerance, myoglobinuria, "second wind" phenomenon | ### High-Yield: **Second wind phenomenon** in Type V occurs because: 1. Initial exercise → glycogen cannot be mobilized (phosphorylase deficient) 2. Ischemic conditions develop → blood flow increases 3. Increased glucose uptake from blood (via GLUT4) bypasses the phosphorylase block 4. Energy production resumes → symptoms improve ### Clinical Pearl: Type III (Cori disease) patients have *some* ability to mobilize outer branches of glycogen via debranching enzyme, making it clinically milder than Type I. However, the accumulated glucose-6-phosphate still enters glycolysis, producing lactate—just not to the extreme degree seen in Type I. ### Mnemonic: **"LAMP"** for lysosomal storage disorders — Type II (Pompe) is the only GSD that is lysosomal (Lysosomal Acid Maltase Pompe).
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