A 2-year-old girl has gait difficulties, progressive spasticity, and regression of speech. MRI shows diffuse white matter changes. Nerve conduction studies reveal a demyelinating peripheral neuropathy. Enzyme assay shows deficient arylsulfatase A activity. What is the accumulated substrate?

• A Galactocerebroside
• B Glucocerebroside
• C Sphingomyelin
• D Sulfatide (cerebroside sulfate) ✓

Explanation

Metachromatic leukodystrophy results from arylsulfatase A deficiency, leading to accumulation of sulfatides in myelin sheaths of the central and peripheral nervous system. Sulfatides stain brownish-yellow with cresyl violet, hence 'metachromatic'. Galactocerebroside accumulates in Krabbe disease (galactocerebrosidase deficiency), sphingomyelin in Niemann-Pick disease, and glucocerebroside in Gaucher disease. The combination of central demyelination plus peripheral neuropathy points specifically to MLD.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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