A 6-year-old girl from North India presents with progressive intellectual disability, coarse facial features, corneal clouding, and hepatosplenomegaly. Enzyme assay reveals deficiency of α-L-iduronidase. Which finding best distinguishes this mucopolysaccharidosis from Hunter syndrome (MPS II)?

Explanation

## Distinguishing Hurler Syndrome (MPS I) from Hunter Syndrome (MPS II) ### Inheritance and Clinical Feature Comparison | Feature | Hurler Syndrome (MPS I) | Hunter Syndrome (MPS II) | |---------|-----|-----| | **Enzyme defect** | α-L-iduronidase | Iduronate-2-sulfatase | | **Inheritance** | Autosomal recessive | **X-linked recessive** | | **Corneal clouding** | **Present (early, prominent)** | **Absent or minimal** | | **Hepatosplenomegaly** | Marked | Marked | | **Coarse features** | Severe | Severe | | **Cardiac involvement** | Valve disease common | Valve disease common | | **Skeletal dysostosis** | Severe | Moderate to severe | | **Gender predominance** | Equal (both sexes) | Males only | ### Key Point: **Corneal clouding is the single best clinical finding that distinguishes MPS I (Hurler) from MPS II (Hunter).** Corneal clouding is a prominent, early feature of Hurler syndrome but is characteristically **absent** in Hunter syndrome. This is the classic clinical discriminator taught in standard references (Nelson's Pediatrics, Robbins Pathologic Basis of Disease). ### Why Option B (X-linked recessive) is INCORRECT here: The question asks which finding **in this patient** best distinguishes MPS I from MPS II. X-linked recessive inheritance is a feature of **Hunter syndrome (MPS II)**, not of the patient described (who has Hurler syndrome, MPS I — autosomal recessive). The question asks for a feature present in this patient's condition (Hurler) that distinguishes it from Hunter. Corneal clouding is present in Hurler and absent in Hunter, making it the correct discriminating finding observed in this patient. ### High-Yield: - **MPS I (Hurler)** = Autosomal recessive, α-L-iduronidase deficiency, **corneal clouding PRESENT** - **MPS II (Hunter)** = X-linked recessive, iduronate-2-sulfatase deficiency, **corneal clouding ABSENT** - Hepatosplenomegaly and coarse facial features are present in **both** conditions — they do NOT distinguish the two. ### Clinical Pearl: The mnemonic: **"Hurler has Hazy corneas; Hunter has no Haze."** Corneal clouding is the hallmark clinical differentiator between these two mucopolysaccharidoses. (Reference: Nelson's Textbook of Pediatrics, 21st ed.; Robbins & Cotran Pathologic Basis of Disease, 10th ed.) ### Mnemonic: **H**urler = **H**azy corneas (corneal clouding present). **H**unter = **H**ide the corneas (corneal clouding absent).