Understanding Alzheimer’s Through Epidemiology

The impact of Alzheimer’s disease on sufferers and those close to them is disastrous. This is a disease for which there is neither curative nor preventative treatment. With the launch of the Alzheimer plan two years ago, Elysée made this disease its hobbyhorse, and the 3C study coordinated by Christophe Tzourio’s neuroepidemiology laboratory (UMRS 708) is one of its flagship projects. This study is based on cohort of over 9000 people, all aged over 65.

At first glance, the association of the terms “epidemiology” and “Alzheimer’s disease” may seem surprising. Alzheimer’s is not really an epidemic, is it ?

Epidemiology is not solely the scientific study of epidemics! The discipline also aims to identify the determinants of diseases, otherwise known as risk factors. From the study of these determinants, hypotheses about the mechanisms of diseases can be made, which are then tested by scientists in other fields of medical research. For example, epidemiology was the first discipline to show that tobacco was responsible for lung cancer. The experimental proof was not provided until several decades later.

Can you explain the concept of a “cohort”?

The principle of a cohort is simple. A group of initially healthy people is constituted. Their clinical and biological characteristics are studied as closely as possible, without bias. They are then monitored for several years in order to detect and diagnose any cases of illness within the group. The comparison between the sick and those who have stayed healthy – fortunately a majority! – allows the precise identification of characteristics that promote the onset of disease.

What are the aims of the 3C study?

The 3C study – or Three Cities study as it is run in Bordeaux, Dijon and Montpellier – is a cohort study which concentrates on brain aging, its causes and its consequences. It was designed and initiated more that 10 years ago by a group of epidemiologists and clinical research scientists who decided to join efforts to carry out this very large study. More specifically, we set ourselves one main objective: to evaluate the significance of vascular risk factors – hypertension and diabetes, for example – in the onset of dementia, with the ultimate goal of being able to implement strategies for the prevention of dementia.

What do you mean by the term dementia?

It’s true that this term can be confusing, but it is a medical term! Here, dementia does not refer to madness – although serious behavioral disorders are common in advanced forms of the disease, which is probably what causes confusion – but to the irreversible damage of cognitive functions, first and foremost memory. Classically, there are considered to be two types of dementia. Neurodegenerative dementia, principally Alzheimer’s disease, results in the impairment by mechanisms still poorly understood of particular zones of the brain, especially those involved in memory. This explains why memory disorders are the first to become obvious, though other disorders follow and eventually all cognitive functions are impaired. Vascular dementia, on the other hand, is due to the occlusion of cerebral vessels causing the destruction of the areas of the brain that they irrigate.

Does the 3C study cover both these types of dementia?

From an epidemiologist’s standpoint, this exclusive distinction between the two types of dementia does not correspond to the way knowledge is developing. There seems to be a continuum between Alzheimer’s disease and vascular dementia, as most patients suffer from both neurodegenerative and vascular lesions. If this hypothesis were verified – and that is one of the aims of the 3C study – it would finally offer opportunities for prevention, as we have an entire armamentarium at our disposal to enable the reduction of vascular risks. Given the enormity of the problem and the current lack of therapeutic tools to fight against this disease, that is a very significant prospect.

Who are the 9 000 elderly people participating in the study?

Thank you for asking this question because I would like to pay them tribute. Even with all the scientists’ efforts, this study would not have existed if normal elderly people living at home had not accepted to give their time and undergo a large number of tests over the last 10 years. Over 3 000 MRI brain scans have been carried out, ultrasound examinations of the carotid artery have been done in over 6 000 people and a bank of biological samples containing DNA has been made for more than 8 000 participants. They underwent these tests graciously, and often volunteered beyond our expectations. It is a real act of generosity: rather than contribute to medical research by giving donations, they gave us their time. Thanks to them, we have been able to constitute one of the biggest databases on brain aging worldwide, which will provide data to work on for generations of scientists and doctors.

What results have you observed so far?

The 3C study has already resulted in over 80 articles in international scientific journals. Among these results, we have been able to specify the role that diet plays in the risk of contracting Alzheimer’s disease, to confirm the predictive role of certain brain anomalies seen on MRI brain scans on the risk of stroke, to identify new genes involved in Alzheimer’s disease, to understand better certain determinants of myocardial depression or infarction, to study the aging of motor functions and of walking in particular, etc. Collectively, these results contribute precious information on the mechanisms of normal aging, as well as on the determinants of the diseases which develop with age. The main goal of 3C is not simply to accumulate knowledge, but to provide data that will enable strategies to be set up to prevent these diseases and to promote better aging. Find out more >> Film (22 mins ): an eyewitness report on the involvement of seniors who participated for 10 years in the 3C study. >> The world’s main cohorts: the Rotterdam Study (The Netherlands), the Framingham heart study (USA).

Find out more 

• Film (22 min) : an eyewitness report on the involvement of seniors who participated for 10 years in the 3C study
• The world’s main cohorts : the Rotterdam Study (The Netherlands), Framingham heart study (USA).