Lincoln's ancestors help trace disease
The discovery, announced Sunday, means that genetic screening can be used to identify people at risk for at least one form of this neurological disease. Perhaps a gene-specific treatment can be designed as well.
Genetics professor Laura Ranum started the hunt for the responsible gene in the early 1990s with one patient who had a family history of ataxia. She then contacted the patient's relatives, hoping that a DNA analysis of the family would expose the origin of a disease that is often passed among generations.
It soon became clear, Ranum said, that this family had a famous ancestor: President Lincoln. It was good fortune. Many relatives had kept detailed family histories because of their famed heritage.
"That was ideal for a genetic mapping study," she said. "What all of the family members seemed to know was how they were related to President Lincoln, not necessarily how they were related to all of the other people."
In one case, a newspaper story in Louisville, Ky., prematurely stated that Ranum's team had traced ataxia back to Lincoln's paternal grandparents, when Ranum had only verified the genetic link to one of Lincoln's uncles. That was fortuitous, though, because descendants of the grandparents then called Ranum and said that ataxia was common on their side of the family.
In the end, Ranum's team interviewed 299 descendants of Lincoln's paternal grandparents, Capt. Abraham Lincoln and Bathsheba Herring. Of that group, 99 had ataxia, according to Ranum's study, which is being published in next month's issue of Nature Genetics. A defect of a single gene was common to all those with the disease.
Children have a 50 percent chance of having the genetic mutation that causes this form of ataxia when one parent has it, Ranum explained. People with the mutation will almost certainly develop ataxia sometime in their lives.
The form of ataxia in the Lincoln descendants is milder but nonetheless can disrupt walking, moving, writing and talking. The disease results when the mutated gene creates abnormal proteins that damage nerve cells in the spinal cord or cerebellum.
The research simply put a name to something that Lincoln descendants already knew: They were more prone to a mysterious ailment. One branch of the family had previously called it the "dreaded Lincoln disease," said Laurie Crary, 50, who is Lincoln's sixth cousin.
Crary, of Prescott, Ariz., isn't as affected as her father, but she and her sister experience vertigo and lose their sense of balance in the dark.
She traveled to the University of Minnesota twice for the research and participated in a battery of dizzying and sometimes nauseating tests. Her great hope is the research will identify treatments in the lifetimes of her daughter and son, who are 21 and 18, respectively. At least, she hopes a definitive screening test will alert her kids to their risk.
She remembered how awareness of ataxia brought her family some comfort.
"It's kind of nice knowing why you stumble in the dark, why you drop things, why you just do really klutzy kind of things," she said.
The university efforts were conducted in coordination with research in Baltimore, Germany and France. Two other families were studied, and while their DNA showed slightly different mutations of the same gene, the end results were the same.
Without genetic testing, researchers don't know whether Lincoln suffered ataxia. He showed symptoms, according to Ranum's study, and also may have suffered from Marfan syndrome, a disorder characterized by long limbs.
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