A 4-year-old girl presents with progressive gait ataxia, loss of deep tendon reflexes followed by extensor plantar responses, and declining speech. MRI shows diffuse white matter changes. Peripheral nerve biopsy demonstrates metachromatic granules that stain brown with cresyl violet. The accumulated substrate and deficient enzyme are:

• A Glucocerebroside; glucocerebrosidase
• B Sulfatides; arylsulfatase A (cerebroside sulfatase) ✓
• C Sphingomyelin; acid sphingomyelinase
• D Galactocerebroside; galactocerebrosidase

Explanation

Metachromatic leukodystrophy results from arylsulfatase B deficiency, causing sulfatide (galactosylceramide 3-sulfate) accumulation in myelin sheaths of the CNS and peripheral nerves, producing demyelination with brown-staining metachromatic granules. Galactocerebroside with galactocerebrosidase deficiency describes Krabbe disease, which lacks the metachromatic staining property. The other options correspond to Gaucher and Niemann-Pick disease, both storage disorders with hepatosplenomegaly rather than primary leukodystrophy.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.