Alzheimer's disease is characterised by a progressive degeneration of the brain's cells, bringing about a decline in intellectual faculties and in memory. Understanding its origin and its first symptoms makes it possible to better support the person affected — and their family.
The disease is characterised by the progressive death of neurons, leading to the loss of certain functions such as memory, reasoning, language, judgement and mood. It affects each person differently: the symptoms, the order in which they appear and the length of each stage vary from one individual to another. In most cases, the disease progresses slowly. It remains incurable, but research has moved forward: two treatments targeting amyloid plaque directly, lecanemab (2023) and then donanemab (2024), have since obtained authorisation in the United States for the early stages of the disease, with a measured slowing of cognitive decline — a change from older treatments, which acted only on the symptoms. Biomarker blood tests, available since 2024, also allow for a diagnosis that is faster and less costly than full brain imaging.
What is the origin of Alzheimer's disease?
A combination of factors specific to each individual could be at the origin of the disease. Among the factors that increase risk are age, genetic factors, head injuries, cardiovascular disease, obesity, metabolic syndrome, uncontrolled high blood pressure and diabetes. Scientific research is looking mainly in two directions: family history and the workings of the human body itself. The 2024 Lancet Commission on dementia prevention estimates that up to 45% of cases could be delayed or avoided by acting on 14 modifiable factors across the whole of life — among them high blood pressure, untreated hearing loss, smoking, obesity, physical inactivity, diabetes, social isolation and, added in 2024, high LDL cholesterol in middle age and untreated vision loss in later life.
Family history
The disease can develop in any individual, including in the absence of any history at all. But if a family member is affected, that doubles, or even triples, the risk of developing the disease for the rest of the family.
The human body
Researchers are seeking to determine whether the disease is caused by a chemical imbalance, a build-up in the brain of substances toxic to neurons (amyloid, free radicals), or an immune deficiency.
What are the first symptoms to watch for?
| Symptom | How it shows itself |
|---|---|
| Memory loss | Frequent lapses, above all about recent events — more marked than the usual small forgettings. |
| Difficulty carrying out familiar tasks | Difficulty preparing a meal or using household appliances that have nonetheless always been familiar. |
| Language problems | Words forgotten or replaced by a word of similar sound ("lion" in place of "violin"). |
| Loss of orientation | Getting lost in one's own street, wandering without knowing how to get home, difficulty naming the day's date. |
| Diminished judgement | Failing to recognise a health problem that needs treating, wearing warm clothes in the middle of a heatwave. |
| Difficulty with abstract tasks | Struggling to understand the figures on a bank statement, difficulty planning a journey with connections. |
| Mislaid objects | Putting an iron away in the freezer, a watch in the sugar bowl. |
| Changes of mood | Going from calm to tears or anger for no apparent reason. |
| Changes of personality | Becoming confused, withdrawn, mistrustful, apathetic or fearful. |
| Loss of interest | Becoming very passive, needing a great deal of encouragement to take part in activities. |
Caring for your brain day by day remains one of the known levers for preserving your cognitive capacities over time — our article Rest and the brain: why switching off costs so much explores precisely the importance of mental rest, and Take up physical activity sets out the benefits of exercise, cognitive ones included.
