Clinical Scenario:
A 16-month-old girl is evaluated for progressive abdominal distension, poor weight gain, and delayed motor milestones. Examination reveals marked hepatosplenomegaly, muscle hypotonia, and features of chronic liver disease. Laboratory investigations show mildly elevated transaminases with normal lactate and serum uric acid levels. Liver biopsy demonstrates accumulation of glycogen with abnormally long, poorly branched chains. Which enzyme deficiency is responsible for this disorder?
A. Acid α-glucosidase
B. Branching enzyme (amylo-1,4→1,6-transglucosidase)
C. Debranching enzyme (amylo-1,6-glucosidase)
D. Glucose-6-phosphatase
E. Liver glycogen phosphorylase
Correct answer & Explanation:
Correct Answer:
B. Branching enzyme (amylo-1,4→1,6-transglucosidase)
Explanation: Glycogen Storage Disease Type IV (Andersen disease)
Glycogen Storage Disease Type IV (Andersen disease) is caused by glycogen branching enzyme (GBE1) deficiency, resulting in the formation of poorly branched, insoluble glycogen (polyglucosan bodies). These abnormal glycogen molecules are toxic and trigger progressive fibrosis and cirrhosis of the liver.
Typical clinical features include:
- Progressive hepatosplenomegaly
- Failure to thrive
- Hypotonia and delayed motor development
- Progressive liver fibrosis leading to cirrhosis and portal hypertension
- Liver failure usually develops in early childhood
Unlike Von Gierke disease (GSD I), lactic acidosis, severe fasting hypoglycemia, hyperuricemia, and hypertriglyceridemia are not characteristic of GSD IV.
Why the other options are incorrect
- A. Acid α-glucosidase → Causes GSD II (Pompe disease), characterized by hypertrophic cardiomyopathy, hypotonia, and lysosomal glycogen accumulation.
- C. Debranching enzyme → Causes GSD III (Cori disease), presenting with hepatomegaly, fasting hypoglycemia, and skeletal muscle involvement, but not progressive cirrhosis due to polyglucosan accumulation.
- D. Glucose-6-phosphatase → Causes GSD I (Von Gierke disease), associated with severe fasting hypoglycemia, lactic acidosis, hyperuricemia, and hyperlipidemia.
- E. Liver glycogen phosphorylase → Causes GSD VI (Hers disease), which usually presents with mild hepatomegaly and mild fasting hypoglycemia.
High-Yield Exam Pearl
The distinguishing feature of GSD IV is the accumulation of abnormal, poorly branched glycogen (polyglucosan bodies), leading to progressive liver cirrhosis rather than severe metabolic abnormalities.
You can also practice another MCQ on Storage disorder.
References
- Magoulas PL, El-Hattab AW. Glycogen Storage Disease Type IV. In: Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026. Updated August 1, 2019.
- Kliegman RM, St Geme JW III, Blum NJ, Shah SS, Tasker RC, Wilson KM, editors. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia: Elsevier; 2024.
- Moses SW, Parvari R. GSD IV: glycogen branching enzyme deficiency and its clinical spectrum. Mol Genet Metab. 2002;75(1):1-7.
