A 3-year-old boy from Tamil Nadu 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 spleen 8 cm below the costal margin. Bone marrow aspirate shows foamy macrophages. Serum acid phosphatase is markedly elevated. What is the most likely diagnosis?

## Clinical Diagnosis: Hurler Syndrome (MPS Type I) **Key Point:** Hurler syndrome (Mucopolysaccharidosis Type I) is caused by deficiency of **α-L-iduronidase**, leading to accumulation of dermatan sulfate and heparan sulfate in lysosomes of multiple tissues, producing the classic triad of coarse facial features, corneal clouding, and hepatosplenomegaly. ### Why Hurler Syndrome Fits This Case | Feature | Hurler Syndrome | Gaucher Disease | Niemann-Pick | Fabry Disease | |---------|-----------------|-----------------|--------------|---------------| | **Age of onset** | 6–24 months | Variable | Infancy | Childhood–adulthood | | **Hepatosplenomegaly** | Marked | Marked | Marked | Absent | | **Coarse facial features** | **Present (hallmark)** | Absent | Absent | Absent | | **Corneal clouding** | **Present (hallmark)** | Absent | Absent | Absent | | **Developmental delay** | Progressive | Type 2/3 only | Present | Absent | | **Bone marrow cells** | Foamy macrophages | Gaucher cells (wrinkled tissue paper) | Sea-blue histiocytes | Not typical | | **Enzyme deficiency** | **α-L-iduronidase** | Glucocerebrosidase | Sphingomyelinase | α-galactosidase A | ### Clinical Features Pointing to Hurler Syndrome 1. **Coarse facial features** — a hallmark of mucopolysaccharidoses; caused by GAG deposition in soft tissues of the face. 2. **Corneal clouding** — pathognomonic for Hurler syndrome among lysosomal storage disorders; results from GAG accumulation in the corneal stroma. 3. **Hepatosplenomegaly** — due to GAG-laden macrophage infiltration of liver and spleen. 4. **Developmental delay** — progressive neurological involvement is characteristic of Hurler syndrome (MPS IH). 5. **Foamy macrophages on bone marrow aspirate** — GAG-laden macrophages appear foamy on histology. 6. **Recurrent respiratory infections** — due to airway GAG deposition causing narrowing and secretion retention. **High-Yield:** Corneal clouding is NOT seen in Gaucher disease or Niemann-Pick disease. Its presence in this vignette, combined with coarse facial features, strongly points to a mucopolysaccharidosis (Hurler syndrome) rather than a sphingolipidosis. ### Why Gaucher Disease Is Incorrect - Gaucher cells have a characteristic **"wrinkled tissue paper"** appearance, NOT foamy macrophages. - **Corneal clouding is absent** in Gaucher disease — this is a key distinguishing feature. - **Coarse facial features** are not a feature of Gaucher disease. - Elevated acid phosphatase can be seen in multiple lysosomal storage disorders and is not specific enough to override the clinical picture. ### Diagnostic Confirmation - **Enzyme assay:** Markedly reduced α-L-iduronidase activity in leukocytes or fibroblasts. - **Urine GAG analysis:** Elevated dermatan sulfate and heparan sulfate. - **Genetic testing:** IDUA gene mutations. - **Skeletal survey:** Dysostosis multiplex (J-shaped sella, oar-shaped ribs, bullet-shaped vertebrae). **Clinical Pearl:** Among lysosomal storage disorders, **corneal clouding + coarse facial features + hepatosplenomegaly + developmental delay** = Hurler syndrome until proven otherwise. (Robbins Basic Pathology, 10e, Ch. 5; Nelson Textbook of Pediatrics, 21e) **Mnemonic:** **HURLER** = **H**epatomegaly, **U**gly (coarse) facies, **R**espiratory issues, **L**ysosomal enzyme defect (α-L-iduronidase), **E**yes (corneal clouding), **R**etardation (developmental delay). [cite:Robbins 10e Ch 5; Nelson Textbook of Pediatrics 21e]