A 6-month-old boy has coarse facial features, cloudy corneas, organomegaly, and skeletal dysplasia (dysostosis multiplex on X-ray). Urine shows elevated heparan sulfate and dermatan sulfate. Enzyme assay confirms deficiency of iduronate-2-sulfatase. This is:

• A MPS II (Hunter syndrome) — iduronate-2-sulfatase deficiency, X-linked ✓
• B MPS I (Hurler syndrome) — alpha-L-iduronidase deficiency
• C MPS III (Sanfilippo) — heparan-N-sulfatase deficiency
• D MPS IV (Morquio) — galactosamine-6-sulfatase deficiency

Explanation

MPS II (Hunter syndrome) is caused by deficiency of iduronate-2-sulfatase, resulting in accumulation of heparan sulfate and dermatan sulfate. It is the only X-linked MPS (all others are autosomal recessive), thus predominantly affecting males. Key distinguishing features from Hurler (MPS I): Hunter syndrome does NOT cause corneal clouding (Hurler does), is X-linked, and has a milder attenuated form. Both cause coarse facies, dysostosis multiplex, organomegaly, and intellectual disability. Treatment with enzyme replacement therapy (idursulfase) is available. Sanfilippo predominantly affects CNS with behavioral features and mild somatic involvement; Morquio causes significant skeletal dysplasia with normal intellect.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.