Researchers at the University of Minnesota have discovered a gene mutation in 11 generations of relatives who descended from Lincoln's grandparents.
The gene causes spinocerebellar ataxia type 5, a degenerative neurological disorder that affects coordination, including walking, writing, speaking and swallowing. There's a 25 percent chance that Lincoln also inherited the mutation, said Laura Ranum, a genetics professor who led the research.
"Because the historical literature talks about his clumsy gait ... it raises the possibility that that was caused by a mutation in this gene," Ranum said.
But since Lincoln has no living direct descendants, confirming whether the nation's 16th president had the defective gene would require that his DNA be taken from historical artifacts and tested, an issue that has been debated over the years.
"What historical purpose would it serve? It (wouldn't) change the facts of how he became a great president," said Kim Bauer, Lincoln curator at the Abraham Lincoln Presidential Library and Museum in Springfield, Ill. "I would fall on the side of leaving President Lincoln alone."
The new findings on the ataxia gene were reported this week in the online edition of the journal Nature Genetics. Since 1992, the Minnesota researchers have studied more than 300 members of the Lincoln family. About one-third of them have ataxia.
Terry Smith and Laurie Crary, both ataxia sufferers and descendants of Abraham Lincoln's uncle Josiah Lincoln, said they would like to know if the president had their disease.
"If a president had it, and he was disabled but still running the country, maybe people would lighten up on disabled people a little bit," said Smith, 57, of Manteca, Calif., who said he was once arrested for drunken driving because of the disease's symptoms.
Crary, 50, of Prescott, Ariz., said she has vertigo and had to have reconstructive surgery on her shoulder after losing her coordination and falling. If Lincoln had ataxia, that could offer hope for others suffering from it. About 150,000 Americans have the degenerative disease.
"Look what he achieved, even if he had this defective gene," Crary said.
In the 1990s, a geneticist asked the National Museum of Health and Medicine to test Lincoln's hair and bones to find out if the president had Marfan syndrome, a disorder that affects connective tissue, blood vessels and eyes, and can produce fatal abnormalities of major arteries. Marfan's sufferers often have unusual height and elongated fingers, toes and limbs, all characteristics of Lincoln.
But multiple panels decided "the greater public good is served by not destroying this non-renewable national historic treasure," according to the museum's Web site.
Bauer, the Lincoln museum curator, said that when Lincoln's tomb was renovated about 100 years ago, his last living son made it clear he did not want his father's remains disturbed.
That should be an overriding factor, Bauer said.
"His last living descendant, still alive, saying, 'Don't bother my father anymore.' ... If DNA testing was alive in the early 1900s, I think he would say the same thing," he said.
Ranum said researchers would need a small amount of Lincoln's DNA to test for the gene, which causes spinocerebellar ataxia type 5, or SCA5. The DNA could be found on a bloodstained garment or a hair sample. She said she would pursue a DNA test if the opportunity arose, but for now, her main concern is science.
Dr. Robert Y. Moore, a movement disorder specialist and a professor of neurology at the University of Pittsburgh, said the Minnesota research breaks ground "from the perspective that this is a mutation in a gene that has not been known to be involved in this sort of thing before."
For now, Ranum said the new discovery should lead to better diagnosis and possible future treatments and may help people decide whether to have children. The mutated gene is dominant, so there is a 50 percent chance a parent will pass it on.
Still, she said finding out whether Lincoln had the gene could help destigmatize the disease.
"Every aspect of Lincoln's life has been gone over with a fine-tooth comb," she said. "I think it is of historical interest."