A vehicle drives on a road in Tokyo July 12, 2009. REUTERS/Stringer

WASHINGTON (Reuters) - No need to curse that bad driver weaving in and out of the lane in front of you -- he cannot help it, U.S. researchers reported on Wednesday.

They found that people with a particular gene variant performed more than 20 percent worse on a driving test than people with a different DNA sequence.

The study may explain why there are so many bad drivers out there -- about 30 percent of Americans have the variant, the team at the University of California Irvine found.

“These people make more errors from the get-go, and they forget more of what they learned after time away,” Dr. Steven Cramer, who led the study published in the journal Cerebral Cortex, said in a statement.

Cramer and his team tested 29 people -- 22 without the gene variant and seven who had it -- asking them to drive 15 laps on a simulator and then repeat the task a week later.

To their surprise, they found that those with the mutant gene did worse, consistently.

The gene controls a protein called brain-derived neurotrophic factor, which affects memory.

The team was not really looking for insights into driving but chose the driving test because it uses common skills.

“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.”