When you apply for a mortgage in 10 years, you may be asked for your bank statements, your pay stubs and a cheek swab. At least that s one possible implication of a new study, which reports a groundbreaking finding: that whether you carry a specific gene variant can predict your propensity to rack up credit-card debt.

Specifically, Jan-Emmanuel De Neve, of the London School of Economics, and James Fowler, of the University of California, San Diego, have found that if you carry one or both low efficiency alleles of the MAOA gene we ll get to what exactly the MAOA gene is and does in a minute the likelihood that you have credit card debt increases by 8% and 16%, respectively.

It s a first-of-its-kind result, but what exactly does it mean? Does it mean that humans carry a debt gene ? And if you were to carry such a gene, does that mean you re doomed to a life of financial turbulence and tribulation?

To begin to answer these questions, one must understand the complex relationship between genes and behavior. Unlike with physical characteristics (such as eye color), behavioral traits (such as violence or impulsivity) are tricky to identify and arise from a tremendously complex interplay of brain systems and environment.

The heritability of human behavior has been studied systematically since the 19th century. Traditionally, it s been studied using twins and adoptees, to tell us how much of a trait is explainable purely by genetics, as opposed to environmental or other influences. And that approach has been extremely fruitful. Recent twin studies, for instance, have shown us that some surprising things have major genetic components: risk-taking, the tendency to cooperate, happiness levels, political preferences even whether or not a person is likely to turn out to vote, donate to a political candidate, or run for office him or herself.

The rising availability of DNA analyses, however, is now making it possible for scientists to try to link specific genes to specific behaviors.

So, is there a debt gene ?

There will never, ever be such a thing as a debt gene , says De Neve. But what humans likely have is a set of genes whose expression, in combination with environmental factors, influences financial decision-making.

The MAOA gene appears to be one of these genes.

The reason there can t be a debt gene, as such, is simple. Debt isn t a discreet human trait. It arises from other traits, such as being impulsive or overvaluing immediate gains compared to future costs. And even these underlying traits don t arise from a single gene, but from a host of genetic and environmental factors.

All that said, there s a reason De Neve and Fowler chose the MAOA gene for study. The gene encodes an enzyme that degrades neurotransmitters such as serotonin, dopamine, and adrenaline in parts of the brain that regulate impulsiveness and cognitive ability. Some versions of this gene are less efficient at producing this enzyme than others. The two low-efficiency types have been linked in previous studies to traits such as lack of conscientiousness, impulsivity, and addictive behavior.

Given this background, De Neve and Fowler looked at a genetic database of more than 2,500 U.S. 18- to 26-year-olds who have been tracked since high school in the National Longitudinal Study of Adolescent Health, which looks at the health-related behavior of young people and follows them into adulthood.

De Neve and Fowler predicted that those in the database with the low-efficiency MAOA genes would report higher incidence of carrying credit card debt and that s exactly what they found.

De Neve s and Fowler s finding has yet to be replicated. And, as the authors admit, it would be better to look at older adults and to have verifiable information about their actual amount of credit card debt. But the implications are nonetheless far-reaching.

First of all, roughly half the people in the sample had the low-efficiency MAOA gene. And, since the sample was representative of the U.S. population, that likely means that about half of all Americans are walking around with this debt-correlated gene.

Second of all, individuals have no guarantee under the law that this genetic information is private. In 2008, President Bush signed into law the Genetic Information Nondiscrimination Act, but that law only deals with health insurers and employers it says nothing about lenders or other financial institutions.

Of course, lenders ought not make the mistake of buying into genetic determinism any more than economists can continue to buy into the blank slate theory of human nature, where individuals are identical automatons, influenced only by the outside world.

The fact is that humans are not blank slates but neither is their destiny written in their genes. Genes set the table, but everything that happens in a person s life and every choice he or she makes along the way determines the outcome.

And that s something you can t test with a cheek swab.

Ryan Sager writes the blog Neuroworld at TrueSlant.com.