22 January 2007
ByAppeared in BioNews 392
New research published early online in the journal Nature Genetics has linked mutations in the SORL1 gene with an increased risk of developing Alzheimer's disease.
Alzheimer's disease is a progressive, degenerative and irreversible brain disorder that causes intellectual impairment, disorientation and eventually death. It is estimated that 2-5 per cent of people over 65 years of age and up to 20 per cent of those over 85 years of age suffer from the disease. It is caused by a complicated interaction of many genetic, environmental and life-style risk factors.
The new research finally confirms the suspected link between Alzheimer's disease and the way in which amyloid protein is processed in the brain. While amyloid protein is itself harmless, it is thought to cause neurological damage when it is broken down and transformed into toxic fragments of beta-amyloid. The SORL1 gene produces a protein which appears to help get rid of the build up of these toxic beta-amyloid fragments.
The international team of researchers was led by scientists from Columbia University Medical Centre, Boston University School of Medicine and the University of Toronto. The teams examined blood samples from 6861 people from different ethnic and racial groups, 46 per cent of whom had Alzheimer's. Several versions of the gene were discovered, with one particular variant being more prevalent in Alzheimer's patients. It was also shown that Alzheimer's patients had lower levels of the SORL1 protein in their blood, which may lead to an increase in the toxic beta-amyloid fragments thought to cause the damage. This is in agreement with previous studies, which show that people who have Alzheimer's disease have reduced levels of several proteins involved in processing amyloid.
Clive Ballard, director of research at the Alzheimer's Society in the UK, told the BBC, 'This latest study is exciting because it suggests the SORL1 gene plays a significant role in the recycling and disposal of amyloid protein and late-onset Alzheimer's disease. The results put the spotlight on an important new area for the development of drugs and treatment targets to tackle Alzheimer's disease'.