What is Alzheimer’s disease?

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Alzheimer’s disease is caused by the progressive loss of neurons (neurodegenerative disease) which prevents the nervous system from functioning correctly. It should not be considered a normal part of ageing.

The most frequent symptom and characteristic feature of Alzheimer’s disease is forgetfulness. It occurs frequently (several times a day), continuously (day after day for months on end), significantly (patients forget important things, not just trivial matters) and progressively (they forget increasingly more things and of increasing importance).

However, forgetfulness is not the only symptom. Neurodegeneration disrupts the normal function of the brain’s neural circuits that manages the memory, but as the disease progresses it also affects other areas of the brain responsible for cognitive skills, such as language, orientation, ability to complete tasks, etc., and emotional reactions.

Stages and types of Alzheimer’s disease

Depending on the degree to which the patient’s cognitive capacity to carry out daily activities has been affected, Alzheimer’s can be separated into two long stages:

Stage of mild cognitive impairment

Stage of mild cognitive impairment. This is when the patient and/or those around them notice the onset of memory loss which is confirmed during a professional evaluation. At this stage, the memory loss does not stop the patient from completing their everyday activities.


Stage of dementia. In the dementia stage, the cognitive problems mean the patient requires a varying degree of supervision or help with day-to-day activities and so they are no longer fully independent.

Based on the patient’s age at the onset of the disease, they are categorised as having:

Late-onset Alzheimer’s

Late-onset Alzheimer’s. This corresponds to patients whose symptoms first develop over the age of 65. It is the most common type given that onset occurs in people aged over 65 in 9 out of 10 cases.

Early-onset Alzheimer’s

Early-onset Alzheimer’s. Defined as cases in which the symptoms initially manifest in individuals under the age of 65 (usually between 50 and 65 years).

Furthermore, depending on genetic factors, patients are categorised as having:


Sporadic or polygenic Alzheimer’s disease. In most people with Alzheimer’s disease, genetic factors may play a role in its onset (risk markers) but they are not the cause of the disease. In other words, it is not transmitted from parents to children.

family, hereditary factors

Genetic or autosomal dominant Alzheimer’s disease. This is a very rare type–it represents less than 1 in every 200 cases of Alzheimer’s disease. In these cases, the condition is caused by a genetic mutation that is passed down from parent to child. Genetic Alzheimer’s disease usually develops at a very early age (20–50 years).

How common is Alzheimer's disease?

Alzheimer’s is the most common type of neurodegenerative disease and dementia; it is responsible for 7 out of 10 cases of dementia.

It is calculated that: 100,000 people suffer from dementia in Catalonia; 700,000 people suffer from dementia across Spain; and 50 million people worldwide have dementia.

It is now more prevalent than a few decades ago because the global population’s life expectancy has increased and it will continue to affect increasingly more people in the next few decades.

According to the World Health Organisation (WHO), a new case is diagnosed every 3 seconds, which is equivalent to 10 million new cases per year. In 2050, more than 150 million people worldwide will suffer from Alzheimer’s disease. The cost associated with Alzheimer’s disease and other types of dementia represents 1% of the world’s GDP.

Substantiated information by:

Neus Falgas Martínez
Raquel Sanchez del Valle Díaz
Soledad Barreiro Gigan

Published: 9 April 2018
Updated: 9 April 2018


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