Alzheimer's disease (AD) is a neurodegenerative disorder that causes cognitive impairment and behavioral disorders. It is characterized, in its typical form, by a loss of memory and other mental abilities that worsen as different areas of the brain atrophy. It is the most common form of dementia, affecting more than 32 million people worldwide.
The exact causes of Alzheimer's disease are unknown, although research has shown the presence of neuronal damage, with loss of connections and cell death.
The development of AD appears to be triggered by a combination of genetic and environmental factors that affect the brain over time. There are also cases of familial Alzheimer's disease, caused by point mutations, but they account for less than 1% of the total. Among the most important risk factors, the following stand out:
- Age: this is the most important risk factor, with a significant increase in cases after the age of 65.
- Family history: the risk of developing Alzheimer's disease increases if there is a first-degree relative affected. The APOE4 gene is the most studied.
- Down syndrome. Many people affected by Down syndrome develop Alzheimer's disease in adulthood, probably due to the presence of three copies of chromosome 21.
- The incidence is slightly higher in women than in men.
- Presence of mild cognitive impairment.
- Head trauma.
- Cardiovascular disease.
Alzheimer's disease is the most common cause of neurodegenerative disorders in the elderly. It is estimated that approximately 60% of Alzheimer's disease sufferers have cases in their families. With the exception of those in whom the disease is caused by mutations in a single gene, the vast majority of AD cases appear to be of complex origin, involving susceptibility genes and environmental factors. In a meta-analysis involving more than 53,000 Alzheimer's disease diagnoses and some 350,000 controls, 38 susceptibility loci were identified. Among them, the APOE haplotype stands out as the main genetic risk factor, involved in lipid transport in the organism, being the main apolipoprotein found in the central nervous system. In addition, the NECTIN2 gene, which codes for a cell adhesion protein involved in the homeostasis of astrocytes and neurons and in the formation of synapses, also stands out.
The damage begins years before the onset of symptoms. However, early diagnosis is important for a good therapeutic approach. The most common signs and symptoms of dementia of Alzheimer's type are:
- Memory impairment, especially short-term.
- Difficulty concentrating, planning or solving problems.
- Inability to draw or copy figures.
- Problems completing routine tasks.
- Visual or spatial difficulties that may lead those affected to put things in the wrong places or even get lost.
- Language problems.
- Changes in mood, behavior and personality.
- In more advanced stages, motor function and regulation of our internal organs may be affected.
Mechanisms that allow total prevention of Alzheimer's disease are not known at this time. However, there is strong evidence that several factors related to a healthy lifestyle can reduce the risk of Alzheimer's disease and other types of dementia.
Studies conducted so far suggest that regular exercise, healthy eating and maintenance of brain activity through lifelong learning have a protective effect against Alzheimer's disease.
In addition, controlling blood pressure and blood glucose levels and avoiding alcohol and tobacco consumption also seem to have the effect of reducing the risk of dementia.
13.5 million variants
Schwartzentruber J, Cooper S, Liu JZ, et al. Genome-wide meta-analysis, fine-mapping and integrative prioritization implicate new Alzheimer's disease risk genes. Nature Genetics. 2021 Mar;53(3):392-402.
National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Health Sciences Policy; Committee on Preventing Dementia and Cognitive Impairment.Downey A et al. National Academies Press (US); 2017.