A 3-year-old boy from rural Maharashtra presents with progressive hepatosplenomegaly, developmental delay, and recurrent respiratory infections over the past 18 months. On examination, he has coarse facial features, corneal clouding, and a palpable liver edge 4 cm below the costal margin. His urine shows elevated heparan sulfate and dermatan sulfate. Bone marrow aspiration reveals foamy macrophages. What is the most likely diagnosis?

Explanation

## Diagnosis: Mucopolysaccharidosis Type I (Hurler Syndrome) ### Clinical Presentation The constellation of features in this 3-year-old boy is pathognomonic for MPS I (Hurler syndrome): - **Coarse facial features** (broad nose, full lips, short stature) - **Corneal clouding** (distinctive finding) - **Hepatosplenomegaly** (from lysosomal accumulation) - **Developmental delay** (CNS involvement) - **Recurrent infections** (immune dysfunction) - **Elevated urinary glycosaminoglycans** (heparan and dermatan sulfate) ### Pathophysiology **Key Point:** MPS I results from deficiency of **α-L-iduronidase**, leading to accumulation of heparan sulfate and dermatan sulfate in lysosomes throughout the body. 1. Enzyme deficiency → lysosomal accumulation of GAGs 2. Cellular dysfunction → hepatosplenomegaly, coarse features, CNS involvement 3. Urinary excretion → elevated heparan and dermatan sulfate ### Diagnostic Criteria | Feature | MPS I (Hurler) | Gaucher | Niemann-Pick C | | --- | --- | --- | --- | | **Enzyme defect** | α-L-iduronidase | Glucocerebrosidase | NPC1/NPC2 protein | | **Stored substrate** | Heparan, dermatan sulfate | Glucocerebroside | Cholesterol, glycosphingolipids | | **Corneal clouding** | Yes (classic) | No | No | | **Urinary GAGs** | Elevated | Normal | Normal | | **Bone marrow** | Foamy macrophages | Gaucher cells (wrinkled tissue paper) | Foam cells | | **Age of onset** | 6–24 months | Variable (infantile to adult) | Infantile to juvenile | ### High-Yield Features of MPS I **High-Yield:** The **triad of corneal clouding + coarse features + elevated urinary GAGs** is virtually diagnostic of MPS I. **Mnemonic — MPS I complications: "CHOPS"** - **C**orneal clouding - **H**epatosplenomegaly - **O**steodystrophy (skeletal dysplasia) - **P**rogressive CNS involvement - **S**hort stature ### Management **Clinical Pearl:** Enzyme replacement therapy (imiglucerase) and hematopoietic stem cell transplantation (HSCT) are the only disease-modifying treatments; early intervention improves outcomes. ## Why This Is the Best Answer The **combination of corneal clouding + elevated urinary heparan/dermatan sulfate + foamy macrophages + coarse features in a 3-year-old** is the gold standard presentation for MPS I. No other lysosomal storage disorder presents with this exact triad.