Towards early diagnosis of AD
Alzheimer’s disease (AD), a progressive and eventually fatal neurodegenerative condition, was first described over a century ago. The prevalence of the disease has greatly increased since then: indeed the World Health Organization estimates that around 36 million people are living with dementia, the majority of whom are suffering from AD. This number is expected to double by 2030 and triple by 2050, mostly due to increased human longevity: the incidence of AD increases exponentially after the age of 65, with nearly 50% of people over 85 affected. Very early diagnosis and timely and effective therapy are urgently needed if health and social services are not to be totally overwhelmed catering for the needs of both patients and their frequently elderly carers.
Changes in the brains of AD patients may commence up to two decades before clinical symptoms become apparent. The two major abnormalities, beta-amyloid plaques (Aβ) and neurofibrillary tangles (NFT), are very visible at autopsy and continued improvements in medical imaging technologies may allow eventual visualization in the brains of living patients. A definitive diagnosis of AD, though, is usually still based on neuropsychological testing and MRI and/or CT scans to rule out other causes of cognitive decline at a stage of the disease when the drugs currently available, which regulate neurotransmitters, are no longer very effective.
Ongoing research to allow earlier diagnosis has found that gradually increasing concentrations of both Aβ and NFT can be detected in the cerebrospinal fluid of AD patients. And two very recently published studies give additional cause for optimism. The first, published in Nature Genetics, was a large international study that scanned the DNA from more than 74,000 AD patients and healthy controls from 15 different countries to find novel genetic risk factors. As well as the genes already implicated in the disease, such as APOE4, which is strongly linked to late-onset AD, eleven new genes were discovered that had previously not been linked to the condition. This work could facilitate very early diagnosis in individuals at risk. And a smaller British Medical Research Council study discovered a compound that actually prevents further neurodegeneration in animal models.
It has been recognized, however, that an international approach would be most effective in reducing the impact of AD and other types of dementia. To this end health ministers from the G8 countries will be meeting in London in December to develop a coordinated plan of action. It is to be hoped that the result of their deliberations will be global cooperation between companies, researchers and clinicians, and ultimately timely diagnosis and therapy for this appalling condition.