A 55-year-old man with 15 years of poorly controlled type 2 diabetes develops bilateral cataracts. Lens epithelial cells accumulate excess intracellular sorbitol. Which enzyme is responsible for converting glucose to sorbitol in the lens?

• A Galactitol synthetase
• B Sorbitol dehydrogenase
• C Aldolase B
• D Aldose reductase ✓

Explanation

In hyperglycemia, glucose enters the polyol pathway where aldose reductase reduces it to sorbitol using NADPH. Sorbitol accumulates in lens fibers because sorbitol dehydrogenase activity there is low, and the osmotically active sugar alcohol draws water in, causing cataract. The same mechanism damages Schwann cells in diabetic neuropathy. Sorbitol dehydrogenase performs the next step, not the first.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.