A 6-month-old infant of consanguineous parents presents with progressive developmental regression, hyperekplexia, and a cherry-red spot on fundoscopy. He had normal development until 4 months. Enzyme assay shows deficiency of hexosaminidase A. What is the mode of inheritance?

• A Autosomal recessive ✓
• B Autosomal dominant
• C X-linked recessive
• D Mitochondrial inheritance

Explanation

This is Tay-Sachs disease (GM2 gangliosidosis type 1), caused by deficiency of hexosaminidase A, leading to accumulation of GM2 ganglioside in neurons. It presents with psychomotor regression after a period of normal development, exaggerated startle (hyperekplexia), and the pathognomonic cherry-red spot at the macula (where gangliosides accumulate in surrounding retinal ganglion cells but not in the fovea). It is inherited in an autosomal recessive pattern; consanguinity increases risk. There is no effective treatment; prognosis is fatal by 2-5 years.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.