Some people really are just bad drivers. That's according to new research suggesting individuals born with a certain variant of a gene don't stay on the road as well as their counterparts.

If the results do in fact hold up, and this gene equals bad driving, 30 percent of Americans would fall into that category, according to the study scientists.

The study involved only 29 individuals, however, 22 without the so-called bad-driving gene and seven with it. The participants drove 15 laps on a simulator that required them to learn the nuances of a track with difficult curves and turns. The researchers measured how well participants stayed on course. The drivers repeated the simulator test four days later.

Participants with this particular gene performed 20 percent worse on the simulation test compared with those without the gene variant. Similar results were found in the follow-up test.

Such a small study would need to be replicated by other research, but here's what the researchers think is going on:

The gene in question limits the availability of a protein called brain-derived neurotrophic factor (BDNF) during activity. This protein strengthens a person's memory by supporting communication among brain cells and keeping them in peak shape. When a person is engaged in a particular task, BDNF is secreted in the brain area connected with that activity to help the body respond.

"These people make more errors from the get-go, and they forget more of what they learned after time away," said lead researcher Steven Cramer, neurology associate professor at the University of California, Irvine.

In fact, past research has suggested that when individuals with this variant complete a task a smaller portion of the brain gets stimulated compared with individuals carrying a "normal" type of this gene.

The gene variant isn't always bad, though. Studies have found that people with it maintain their usual mental sharpness longer than those without it when neurodegenerative diseases such as Parkinson's, Huntington's and multiple sclerosis are present.

"It's as if nature is trying to determine the best approach," Cramer said. "If you want to learn a new skill or have had a stroke and need to regenerate brain cells, there's evidence that having the variant is not good. But if you've got a disease that affects cognitive function, there's evidence it can act in your favor. The variant brings a different balance between flexibility and stability."

While a test to determine whether someone has the gene variant is not commercially available, there's a real-world experiment going on.

"I'd be curious to know the genetics of people who get into car crashes," Cramer said. "I wonder if the accident rate is higher for drivers with the variant."

The research, funded by the National Institutes of Health, is detailed in a recent issue of the journal Cerebral Cortex.