A 3-year-old child shows progressive gait ataxia and declining school performance over one year. Peripheral nerve conduction studies reveal a demyelinating polyneuropathy. Urinary sulfatide excretion is markedly elevated, and nerve biopsy shows granular metachromatic material staining brown with cresyl violet. The deficient enzyme is:

• A Galactocerebroside beta-galactosidase
• B Beta-glucocerebrosidase
• C Acid sphingomyelinase
• D Arylsulfatase A ✓

Explanation

Metachromatic leukodystrophy is caused by arylsulfatase A deficiency, leading to lysosomal accumulation of cerebroside sulfate (sulfatide) in myelin-forming cells. It presents in childhood with central demyelination plus a peripheral neuropathy, and stored sulfatide gives the characteristic brown metachromasia with cresyl violet. Galactocerebrosidase deficiency defines Krabbe disease, beta-glucocerebrosidase deficiency Gaucher disease, and acid sphingomyelinase deficiency Niemann-Pick disease type A.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.