All of the following glycogen storage disorders present with hepatomegaly and hypoglycemia EXCEPT:

Explanation

## Glycogen Storage Disorders: Hepatic vs Muscle Phenotypes ### Classification by Primary Organ Involvement | GSD Type | Enzyme Defect | Primary Organ | Hepatomegaly | Hypoglycemia | Muscle Involvement | |----------|---------------|---------------|--------------|--------------|--------------------| | Type I (Von Gierke) | Glucose-6-phosphatase | Liver | **Yes** | **Yes** (severe) | No | | Type III (Cori) | Debranching enzyme | Liver + Muscle | **Yes** | **Yes** (mild) | Mild | | Type V (McArdle) | Muscle phosphorylase | Muscle | **No** | **No** | **Yes** | | Type VI (Hers) | Liver phosphorylase | Liver | **Yes** | **Yes** (mild) | No | ### Key Point: **Type V (McArdle disease) is a muscle-specific glycogen storage disorder.** It does NOT present with hepatomegaly or fasting hypoglycemia because: 1. The enzyme defect (muscle phosphorylase) is confined to skeletal muscle and does not affect hepatic glucose metabolism. 2. Liver can still mobilize glucose via other pathways (debranching enzyme, liver phosphorylase). 3. Patients present with **exercise intolerance, myalgia, and myoglobinuria** ("second wind phenomenon"), not hypoglycemia. ### Clinical Pearl: **High-Yield:** Types I, III, and VI all cause hepatomegaly and hypoglycemia because they impair hepatic glycogenolysis or glucose release. Type V spares the liver entirely — it is a myopathy, not a hepatic disorder. ### Mnemonic: **"Liver disorders = I, III, VI (hepatomegaly + hypoglycemia); Muscle disorder = V (exercise intolerance, no hypoglycemia)"** ### Warning: Do not confuse Type V with Type IV (branching enzyme deficiency, which causes cirrhosis and hepatomegaly). Type V is purely muscular.