In the largest study of its kind, an international research consortium including the University of Toronto’s Tanz Centre for Research in Neurodegenerative Diseases, has identified four new genes linked to Alzheimer’s disease.
The research, undertaken by the Alzheimer’s Disease Genetics Consortium and reported in the current edition of the journal Nature Genetics, details the genetic analysis of more than 11,000 people with Alzheimer’s disease and a nearly equal number of elderly people who have no symptoms of dementia, as well as confirming data which brings the total number of people analyzed to 54,000 from the U.S., Canada, the United Kingdom and Europe.
“Each identified gene adds to the risk of dementia later in life. This information provides great insight into the cause of Alzheimer’s disease,” said Professor Peter St George-Hyslop, Director of the Tanz Centre.
The study is the result of a large collaborative effort with investigators from 44 universities and research institutions in the United States and Canada, led by Professor Gerard Schellenberg at the University of Pennsylvania, with primary analysis sites at Miami, led by Professor Margaret Pericak-Vance and Boston, led by Professor Lindsey Farrer with the Canadian cohort collection led by St George-Hyslop in Toronto.
Until recently, only four genes associated with late-onset Alzheimer’s have been confirmed, including SORL1, which was discovered at the Tanz Centre in 2007 (the current study in Nature Genetics also detected a genetic association between AD and SORL1). The largest effect on risk of late-onset Alzheimer’s Disease is observed for the e4-allele of the apolipoprotein E gene (APOE), which was co-discovered by Drs. Allen Roses, Anne Saunders, Warren Strittmatter and Peter St George Hyslop in 1992. The Nature Genetics study now adds another four — MS4A, CD2AP, CD33, and EPHA1 – and contribute to identifying and confirming two other genes, BIN1 and ABCA7, thereby doubling the number of genes known to contribute late-onset Alzheimer’s disease.
“This is the culmination of years of work on Alzheimer’s disease by a large number of scientists, yet it is just the beginning in defining how genes influence memory and intellectual function as we age. We are all tremendously excited by our progress so far, but much remains to be done, both in understanding the genetics and in defining how these genes influence the disease process,” Schellenberg said.
In 1992, St George-Hyslop and Professor Don Crapper McLachlan reported that a previously unidentified gene in chromosome 14 causes early-onset of Alzheimer’s disease. In 1995, Prof. St George-Hyslop led the team which identified this gene on chromosome 14 (presenilin 1). A few months later he also discovered a second similar gene (Presenilin 2 – located on chromosome 1), which was responsible for a less severe form of familial early-onset Alzheimer’s disease.
The researchers’ ultimate aims are two fold. First, identification of new Alzheimer’s disease genes will provide major clues as to its underlying cause. Genetic studies can provide new insights into the molecules at the center of the disease. Gaining this type of understanding is critical for drug discovery since the currently available treatments are only marginally effective.
Second, gene discovery of the type highlighted in the Nature Genetics article will contribute to predicting who will develop Alzheimer’s disease, which will be important when preventive measures become available. Knowing these risk genes will also help identify the first disease-initiating steps that begin in the brain long before any symptoms of memory loss or intellectual decline are apparent. This knowledge will help researchers understand the events that lead to the destruction of large parts of the brain and eventually the complete loss of cognitive abilities.