Types of Alzheimer’s disease
Alzheimer's disease is a form of dementia most common in older people.
There are three known types of Alzheimer’s disease. Doctors have categorised Alzheimer’s into the following types:
- Early-onset Alzheimer’s. This is a rare form of Alzheimer’s disease in which people are diagnosed with the disease before the age of 65. Fewer than 10% of all Alzheimer’s disease patients have this type. Because they experience premature ageing, people with Down’s syndrome are particularly at risk of a form of early onset Alzheimer’s disease. Adults with Down’s syndrome are often in their mid- to late 40s or early 50s when symptoms first appear. Younger people who develop Alzheimer’s disease have more of the brain abnormalities that are associated with Alzheimer’s disease. Early-onset Alzheimer’s appears to be linked with a genetic defect on chromosome 14, to which late-onset Alzheimer’s is not linked. A condition called myoclonic seizure disorder - a form of muscle twitching and spasm - is also more commonly seen in early-onset Alzheimer’s than in late-onset Alzheimer’s.
- Late-onset Alzheimer’s. This is the most common form of Alzheimer’s disease, accounting for about 90% of cases and usually occurring after age 65. Late-onset Alzheimer’s disease strikes almost half of all people over the age of 85 and hereditary factors may be important in some cases. Late-onset dementia is also called sporadic Alzheimer’s disease.
- Familial Alzheimer’s disease (FAD). This is a form of Alzheimer’s disease that is known to be entirely inherited. In affected families, members of at least two generations have had Alzheimer’s disease. FAD is extremely rare, accounting for fewer than 1% of all cases of Alzheimer’s disease. It has a much earlier onset (often in the 40s) and can be clearly seen to run in families.
Stages of Alzheimer's disease
Doctors classify Alzheimer's disease diagnosis into stages of progression.
Mild Alzheimer's disease symptoms follow a gradual loss of brain function and include:
- Forgetting things and poor memory and forgetfulness
- Mood swings
- Problems with speech
Moderate Alzheimer's disease often adds further symptoms which include:
Delusions, memories of things that didn't happen
- Obsessive or repetitive behaviour
- Poor sleep
Severe Alzheimer's disease can bring:
Testing for Alzheimer's disease
There is no basic test yet for diagnosing Alzheimer's disease, so the diagnosis is usually based on ruling-out other conditions.
One of the goals of research into Alzheimer's disease is better testing to find those at risk before symptoms develop. Researchers hope this will allow for earlier treatment of Alzheimer’s, when it may be more effective. It will also allow for new treatments to be tested before the disease progresses in patients.
In 2010, University College London (UCL) researchers announced work on tests to check for early signs of Alzheimer’s disease in elderly people who appear healthy.
The team says combining spinal fluid tests with MRI scans could provide a useful early indication of a person’s risk of developing the condition.
UK lead international research at Cardiff University in 2011 found five new gene variants linked to Alzheimer's disease.
The research involved analysing the genomes of nearly 40,000 people with and without Alzheimer's. The mammoth task was undertaken by two separate research consortiums in Europe and the US, which collaborated to confirm each other's results.