A 6-month-old infant presents with developmental regression, cherry red spot on fundoscopy, startling hypersensitivity to sound, and progressive hypotonia. The enzymatic deficiency responsible for this condition is:

• A Galactocerebrosidase deficiency
• B Hexosaminidase A (alpha subunit) deficiency ✓
• C Arylsulfatase A deficiency
• D Sphingomyelinase deficiency

Explanation

The clinical triad of progressive neurological deterioration beginning after a normal early period, cherry red spot (due to ganglioside accumulation in perimacular neurons with unmasked retinal pigment), and auditory startle response (hyperacusis) in an infant is classic for Tay-Sachs disease (GM2 gangliosidosis type 1). This is caused by deficiency of hexosaminidase A (HEXA gene), preventing degradation of GM2 ganglioside in lysosomes. Krabbe disease (galactocerebrosidase deficiency) presents with irritability and hypertonicity. Metachromatic leukodystrophy is caused by arylsulfatase A deficiency. Niemann-Pick disease type A is caused by sphingomyelinase deficiency.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.