THE first gene known to cause Alzheimer 's disease in people aged over 65 has been
discovered by American scientists.
Further studies of protein produced by the gene, called STM2, may eventually lead to
a treatment for sufferers, according to a report in Science.
"This is the first time a gene has been shown to cause the late onset of Alzheimer 's disease," said the leader of the research team that made the discovery, Dr Gerry Schellenberg of the Veterans Affairs Medical Centre, Seattle.
The gene was pinpointed during a study of families with a history of Alzheimer 's whose ancestors emigrated to the United States from Russia and Germany during the 19th century.
Two-thirds of those who developed the disease between ages 40 and 82 carried a mutant form of STM2.
Alzheimer 's disease causes shrinkage of the brain, leading to dementia. It rarely occurs
before age 60 but 30 per cent of over-85s are affected by the illness.
Two genes responsible for early onset of the disease, which is known to be inheritable, have already been found. Late onset of the disease has been linked to the ApoE4 gene, which appears to increase the risks but does not cause the disease itself. Environmental factors are also likely to play a role.
In the new study, the STM2 gene was found to be responsible for both early and late onset forms of Alzheimer 's.
All the families tested were thought to be descended from a single common ancestor from a village in the Volga region who carried the mutant gene.
"These families are dispersed across the United States," said Dr Schellenberg. "So there is nothing we can identify as an environmental cause."
Other families displaying a history of Alzheimer 's will now be tested for the mutant gene by Dr Schellenberg and his co-workers.
Cloning of the gene will give an insight into how it leads to the disease. "The gene makes a protein which has some normal function and when it is mutated it has some aberrant function," said Dr Schellenberg. "But we don't know fully what these functions are."
