Bell studies the genetics of diabetes mellitus and the biology of the insulin-secreting pancreatic beta-cell. He cloned and characterized many of the genes that are key in the regulation of glucose metabolism including insulin, glucagon, glucose transporters and many others.

Working with colleague Nancy Cox, PhD, Professor of Medicine and Human Genetics and Section Chief of Genetic Medicine at the University of Chicago, Bell discovered mutations in the genes for glucokinase and for three transcription factors that cause an early-onset form of diabetes called maturity-onset diabetes of the young. Once thought to be very rare, this form of diabetes represents up to 5 percent of cases. Correct genetic diagnosis can alter treatment and improve clinical outcome.