Alzheimer's disease is the most common cause of dementia. The word dementia describes a set of symptoms that can include memory loss and difficulties with thinking, problem-solving or language. These symptoms occur when the brain is damaged by certain diseases, including Alzheimer's disease. This factsheet describes the symptoms of Alzheimer's disease, how it is diagnosed, and the factors that can put someone at risk of developing it. It also describes the treatments and support that are currently available.

Alzheimer's disease, named after the doctor who first described it (Alois Alzheimer), is a physical disease that affects the brain. There are more than 520,000 people in the UK with Alzheimer's disease. During the course of the disease, proteins build up in the brain to form structures called 'plaques' and 'tangles'. This leads to the loss of connections between nerve cells, and eventually to the death of nerve cells and loss of brain tissue. People with Alzheimer's also have a shortage of some important chemicals in their brain. These chemical messengers help to transmit signals around the brain. When there is a shortage of them, the signals are not transmitted as effectively. As discussed below, current treatments for Alzheimer's disease can help boost the levels of chemical messengers in the brain, which can help with some of the symptoms.

Alzheimer's is a progressive disease. This means that gradually, over time, more parts of the brain are damaged. As this happens, more symptoms develop. They also become more severe.

Symptoms
The symptoms of Alzheimer's disease are generally mild to start with, but they get worse over time and start to interfere with daily life.
There are some common symptoms of Alzheimer's disease, but it is important to remember that everyone is unique. Two people with Alzheimer's are unlikely to experience the condition in exactly the same way.
For most people with Alzheimer's, the earliest symptoms are memory lapses. In particular, they may have difficulty recalling recent events and learning new information. These symptoms occur because the early damage in Alzheimer's is usually to a part of the brain called the hippocampus, which has a central role in day-to-day memory. Memory for life events that happened a long time ago is often unaffected in the early stages of the disease.

Memory loss due to Alzheimer's disease increasingly interferes with daily life as the condition progresses. The person may:
• lose items (eg keys, glasses) around the house
• struggle to find the right word in a conversation or forget someone's name
• forget about recent conversations or events
• get lost in a familiar place or on a familiar journey
• forget appointments or anniversaries.

Although memory difficulties are usually the earliest symptoms of Alzheimer's, someone with the disease will also have – or go on to develop – problems with other aspects of thinking, reasoning, perception or communication. They might have difficulties with:
• language – struggling to follow a conversation or repeating themselves
• visuospatial skills – problems judging distance or seeing objects in three dimensions; navigating stairs or parking the car become much harder
• concentrating, planning or organising – difficulties making decisions, solving problems or carrying out a sequence of tasks (eg cooking a meal)
• orientation – becoming confused or losing track of the day or date.

A person in the earlier stages of Alzheimer's will often have changes in their mood. They may become anxious, irritable or depressed. Many people become withdrawn and lose interest in activities and hobbies.

Later stages

As Alzheimer's progresses, problems with memory loss, communication, reasoning and orientation become more severe. The person will need more day-to-day support from those who care for them.

Some people start to believe things that are untrue (delusions) or – less often – see or hear things which are not really there (hallucinations).

Many people with Alzheimer's also develop behaviours that seem unusual or out of character. These include agitation (eg restlessness or pacing), calling out, repeating the same question, disturbed sleep patterns or reacting aggressively. Such behaviours can be distressing or challenging for the person and their carer. They may require separate treatment and management to memory problems.

In the later stages of Alzheimer's disease someone may become much less aware of what is happening around them. They may have difficulties eating or walking without help, and become increasingly frail. Eventually, the person will need help with all their daily activities.

How quickly Alzheimer's disease progresses, and the life expectancy of someone with it, vary greatly. On average, people with Alzheimer's disease live for eight to ten years after the first symptoms. However, this varies a lot, depending particularly on how old the person was when they first developed Alzheimer's. For more information see factsheet 458, The progression of Alzheimer's disease and other dementias and factsheet 417, The later stages of dementia.

Mixed dementia
An estimated 10 per cent of people with dementia have more than one type at the same time. This is called mixed dementia. The most common combination is Alzheimer's disease with vascular dementia (caused by problems with the blood supply to the brain). The symptoms of this kind of mixed dementia are a mixture of the symptoms of Alzheimer's disease and vascular dementia.

Atypical Alzheimer's disease
In some people with Alzheimer's disease the earliest symptoms are not memory loss. This is called atypical Alzheimer's disease. The underlying damage (plaques and tangles) is the same, but the first part of the brain to be affected is not the hippocampus.

Atypical Alzheimer's disease is uncommon in those diagnosed when they are over 65. It accounts for around five per cent of all Alzheimer's in this age group. It is, however, more common in people diagnosed when they are under 65 (early-onset Alzheimer's disease). In this age group it represents up to one-third of cases.

The atypical forms of Alzheimer's disease are as follows:
• Posterior cortical atrophy (PCA) occurs when there is damage to areas at the back and upper-rear of the brain. These are areas that process visual information and deal with spatial awareness. This means the early symptoms of PCA are often problems identifying objects or reading, even if the eyes are healthy. Someone may also struggle to judge distances when going down stairs, or seem uncoordinated (for example when dressing).
• Logopenic aphasia involves damage to the areas in the left side of the brain that produce language. The person's speech becomes laboured with long pauses.
• Frontal variant Alzheimer's disease involves damage to the lobes at the front of the brain. The symptoms are problems with planning and decision-making. The person may also behave in socially inappropriate ways or seem not to care about the feelings of others.

Who gets Alzheimer's disease?
Most people who develop Alzheimer's disease do so after the age of 65, but people under this age can also develop it. This is called early-onset Alzheimer's disease, a type of young-onset dementia. In the UK there are over 40,000 people under the age of 65 with dementia.

Developing Alzheimer's disease is linked to a combination of factors, explained in more detail below. Some of these risk factors (eg lifestyle) can be controlled, but others (eg age and genes) cannot. For more information see factsheet 450, Am I at risk of developing dementia?

Age
Age is the greatest risk factor for Alzheimer's. The disease mainly affects people over 65. Above this age, a person's risk of developing Alzheimer's disease doubles approximately every five years. One in six people over 80 have dementia.

Gender
For reasons that are not clear, there are about twice as many women as men over 65 with Alzheimer's disease. This difference is not fully explained by the fact that women on average live longer than men. It may be that Alzheimer's in women is linked to a lack of the hormone oestrogen after the menopause.

Genetic inheritance
Many people fear that the disease may be passed down to them from a parent or grandparent. Scientists are investigating the genetic background to Alzheimer's. There are a few families with a very clear inheritance of Alzheimer's from one generation to the next. In such families the dementia tends to develop well before age 65. However, Alzheimer's disease that is so strongly inherited is extremely rare.

In the vast majority of people, the influence of genetics on risk of Alzheimer's disease is much more subtle. A number of genes are known to increase or reduce a person's chances of developing Alzheimer's. For someone with a close relative (parent or sibling) who was diagnosed with Alzheimer's when over 65, their own risk of developing the disease is increased. However, this does not mean that Alzheimer's is inevitable, and everyone can reduce their risk by living a healthy lifestyle.

For more information see factsheet 405, Genetics of dementia.

People with Down's syndrome are at particular risk of developing Alzheimer's disease, because of a difference in their genetic makeup. For more information