Learning Objective
Differentiate between Hurler syndrome (MPS I) and Hunter syndrome (MPS II) for NEET PG by focusing on inheritance patterns, specific enzyme deficiencies, and key clinical discriminators like corneal clouding and aggressive behavior.
High-Yield Recall Table
| Feature | Hurler Syndrome (MPS I) | Hunter Syndrome (MPS II) |
|---|---|---|
| Inheritance | Autosomal Recessive (AR) | X-Linked Recessive (XLR) |
| Enzyme Deficiency | α-L-iduronidase | Iduronate sulfatase |
| Accumulated Substrate | Dermatan & heparan sulfate | Dermatan & heparan sulfate |
| Corneal Clouding | Present (+) | Absent (−) |
| Behavior | Normal / Delayed | Aggressive behavior (+) |
| Prognosis & Death | Age < 10 years (Cardiac / CAD) | Adolescence / Early adulthood |
Core High-Yield Concepts for NEET PG
- Pathophysiology: Both are lysosomal storage disorders caused by defective metabolism of glycosaminoglycans (GAGs), leading to widespread extracellular matrix deposition.
- Shared Features: Both conditions present with coarse facial features (frontal bossing, broad nose, flat midface) and hepatosplenomegaly.
Crucial NEET PG Distinctions
- The “Hunter Needs Eyes to Hunt” Mnemonic: Hunters need clear vision to hunt, so Hunter syndrome has NO corneal clouding. Hurler syndrome features severe corneal clouding.
- Inheritance Pattern: Hunter syndrome is X-linked recessive (affects males). Hurler syndrome is autosomal recessive.
- Behavioral Changes: Aggressive behavior is a distinct finding unique to Hunter syndrome.
- Cardiac Mortality: Early mortality in Hurler syndrome (often age < 10) is driven by ischemia and myocardial infarction due to GAG deposition within the coronary arteries.