A study of Mexican Americans has pin-pointed a genetic fault which can lead to heart disease and diabetes.
People with the condition do not process insulin effectively
They have the highest incidence of insulin resistance, which increases the risk of developing the conditions.
Scientists writing in the American journal Diabetes say the discovery could help design treatments to prevent insulin resistance.
Diabetes experts said people might also be able to make lifestyle changes to reduce other risk factors.
'Bar code' variations
Researchers at the Cedar-Sinai Medical Center and the University of California in Los Angeles studied 291 adults whose parents had been diagnosed with heart disease.
Their DNA was tested for six markers for lipoprotein lipase (LPL), a gene that controls the delivery of fatty acids to muscle and tissues in the body.
This "bar code" shows what variations or differences an individual has in their LPL gene, and can give a broader picture than simply looking at one potential variation.
It has been suggested that LPL is linked to high blood pressure, obesity, and atherosclerosis (fatty deposits in the arteries) - all of which are associated with insulin resistance, which also affects the majority of those with Type 2 diabetes.
Researchers also gave patients a test to see how effectively they processed insulin.
If blood sugar levels were too high, it showed cells were not using insulin as they should, and the patient was insulin resistant.
The researchers found eight different "bar code" variations, or haplotypes, among the study group.
They then looked at the level of insulin resistance for each haplotype.
Haplotype 4, carried by 40 patients, was seen to be linked with a high level of insulin resistance, while haplotype, carried by 239, was linked with low levels of insulin resistance.
Haplotype 4 incidence may explain the higher risk of insulin resistance among the Mexican Americans, but more research will have to be carried out before this is confirmed.
Studies will also look at whether the same haplotypes are found in other populations.
Dr Jerome Rotter, director of the Division of Medical Genetics at Cedars-Sinai Medical Center who led the research, said: "This is the first study to definitively show that LPL is a gene for common insulin resistance."
He added: "Our study showed that two separate haplotypes of LPL were linked to low or high levels of insulin resistance, confirming that the LPL gene plays a role in determining insulin resistance in this population of Mexican Americans."
Dr Eleanor Kennedy, Diabetes UK Research Director, said "This is research that has been undertaken in a genetically defined population, and may provide useful information into the possible causes of insulin resistance and Type 2 diabetes.
"However, we will be interested to see further research into the role of the LPL gene in the wider diabetic population.
"If people are aware that they are more likely to develop certain medical conditions, such as diabetes, from studies like this one, they may be able to make lifestyle changes to reduce the other risk factors."