A male infant develops hemolytic anemia, cataracts, and progressive intellectual disability. Urine reducing substance (Clinitest) is positive but glucose oxidase dipstick is negative. Erythrocyte enzyme assay shows absent galactose-1-phosphate uridylyltransferase (GALT). Which metabolite accumulates in the lens and causes cataracts in this condition?

• A Galactose-1-phosphate
• B UDP-galactose
• C Glucose-6-phosphate
• D Galactitol ✓

Explanation

In classic galactosemia (GALT deficiency), galactose accumulates and is reduced to galactitol by aldose reductase in the lens. Galactitol, being a polyol, cannot exit cells and accumulates osmotically causing water influx, lens swelling, and cataracts. Galactose-1-phosphate is the toxic metabolite responsible for liver and CNS damage, but cataracts are specifically due to galactitol accumulation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.