Researchers at Johns Hopkins and the University of Minnesota have discovered a gene mutation in the descendants of Abraham Lincoln's grandparents that suggests the Civil War president himself might have also suffered from a disease that destroys nerve cells in the cerebellum-- the part of the brain that controls movement.
A report on this discovery will appear in the February print issue of Nature Genetics.
The joint finding of the SCA5 mutation comes over a decade after initial speculation that Lincoln might have suffered from Marfan disease. People with this inherited disorder are often tall and thin and can commonly have slender, tapering fingers. The identification of the Marfan gene at Hopkins (Nature 352, 279-81 [1991]) sparked debate concerning testing of President Lincoln's DNA to determine whether his tall stature could have been caused by that disease.
The present discovery in Lincoln's descendants of the gene that causes a movement disorder called spinocerebellar ataxia type 5 (SCA5), however, appears to offer much stronger evidence that the past president himself might have had SCA5, according to Jeffrey D. Rothstein, M.D., Ph.D., a professor of neurology and neuroscience and vice chairman for research in the Department of Neurology at The Johns Hopkins University School of Medicine. SCAs are neurodegenerative disorders that cause loss of coordination of limbs and eye movements, slurred speech and swallowing difficulties.
"Determining President Lincoln's status relative to SCA5 would be of historical interest and would increase public awareness of ataxia and neurodegenerative disease," Rothstein said. The finding also has wider implications because similar mutations might also be associated with other neurodegenerative diseases, the Hopkins researcher said.
The researchers discovered that SCA5 is caused by a mutation of the â-III spectrin gene SPTBN2, which disrupts the ability of certain nerves in the cerebellum to respond normally to incoming chemical signals. Eventually, these nerves -- called Purkinje cells -- degenerate, and the person loses fine control of the leg and arm muscles. This would explain historical descriptions of Lincoln's uneven gait -- an early sign of ataxia -- according to the researchers. Ataxia is an inability to coordinate muscle activity in the arms and legs.
"The discovery by the team of the SCA5 mutations in 90 of 299 descendants of Lincoln could enable us to prove whether Lincoln himself carried the mutation by studying genetic material obtained from artifacts containing his DNA," said Rothstein, a co-author of the Nature Genetics paper.
The researchers found the mutation in all 90 affected individuals (ages 7 to 80 at time of exam) and in 35 descendants of Lincoln who had not yet started to show symptoms of SCA5 (ages 13 to 67 at time of exam), he said. The team also found two other types of mutations in â-III spectrin 2 in a French and German family, respectively. The mutations found in the American, French and German families each affected a different part of the SPTBN2 gene, and thus knocked out a different part of the â-III spectrin protein.
The mutation of the SPTBN2 gene disrupts the normal shape of â-III spectrin, a protein that is key to the proper functioning of Purkinje cells, according to Rothstein, who cloned the protein in 2001 and first described its role in the brain. Specifically, â-III spectrin helps to anchor another protein, called "glutamate transporter EAAT4," into the membrane of the Purkinje cell.