If a gene called MADD is not functioning properly, insulin is not released into the bloodstream to regulate blood sugar levels.
Researchers from the University of Illinois at Chicago College of Medicine found type 2 diabetes could be directly caused by the loss of a properly functioning MADD gene alone.
Professor of microbiology and immunology Bellur Prabhakar said: "Without the gene, insulin can't leave the beta cells, and blood glucose levels are chronically high."
In a healthy person, beta cells in the pancreas secrete the hormone insulin in response to increases in blood glucose after eating.
People with type 2 diabetes do not produce enough insulin or are resistant to its effects so their blood sugar levels become too high.
More than 200,000 people in Scotland have type 2 diabetes, which is linked to obesity.
The findings were reported online in the journal Diabetes.