In diabetes, excess glucose is metabolized via the polyol pathway, aldose reductase (AR) reduces glucose to sorbitol with the help of nicotinamide adenine dinucleotide phosphate (NADPH), and then sorbitol is oxidized to fructose by sorbitol dehydrogenase in a process involving nicotinamide adenine dinucleotide (NAD+). The gene discussed is AKR1B1; the disease is diabetes mellitus.