Discovered -- mechanism of brain activity in Alzheimer's patients

Elevated activity in the hippocampus - the area of the brain that controls learning and memory - is linked with mild cognitive impairment and early stages of Alzheimer's disease. Researchers have now discovered the molecular mechanism that may trigger an enhancement of neuronal activity in Alzheimer's patients, which subsequently damages memory and learning functions. The amyloid precursor protein (APP), in addition to its well-known role in producing a protein fragment known as amyloid-beta, also constitutes the receptor for amyloid-beta.

The binding of amyloid-beta to pairs of APP molecules triggers a signalling cascade, which causes elevated neuronal activity, the study said. 'Our work suggests that APP molecules, like many other known cell surface receptors, may modulate the transfer of information between neurons,' said Inna Slutsky from Tel Aviv University in Israel. Hyperactive hippocampal neurons, which precede amyloid plaque formation, have also been observed in mouse models with early onset Alzheimer's disease. (Read: Could a sleep disorder indicate Alzheimer's or Parkinson's?)

The research project was launched five years ago, following the researchers' discovery of the physiological role played by amyloid-beta, previously known as an exclusively toxic molecule. The team found that amyloid-beta is essential for the normal day-to-day transfer of information through the nerve cell networks. If the level of amyloid-beta is even slightly increased, it causes neuronal hyperactivity and greatly impairs the effective transfer of information between neurons. While unaffected 'normal' neurons became hyperactive following a rise in amyloid-beta concentration, neurons lacking APP did not respond to amyloid-beta. 'This finding was the starting point of a long journey toward decoding the mechanism of APP-mediated hyperactivity,' Slutsky noted. (Read: Could you suffer from Alzheimer's in the future? Take this blood test to find out)

The findings appeared in the journal Cell Reports.

Here are some risk factors of Alzheimer's disease?

Alzheimer's disease (AD) is very complex in nature and it progresses over many years. Its causes are uncertain and hence unknown to us but scientists are trying to look out for factors that may appear to be linked to the development of such disease. These are known as 'risk factors'. This can be related to a person's health, lifestyle, environment, genetic background, etc. The presence of any of the risk factors increases the chance of getting the disease to a much greater extent. In their search for answers, scientists looked for factors which are more common in people who develop AD.

The well established risk factors of Alzheimer's disease are:

Age: Increasing age is the greatest known risk factor in AD. The risk of developing AD appears to double every 5 years in people above 65 years of age. Half of the population develop AD over the age of 85.

Family history of Alzheimer's disease (FAD): Families where members have faced the occurrence of AD among their parents or siblings or other relatives in their last two generations have a greater chance of developing this disease than those with no family history. It is important to remember that Familial Alzheimer's Disease (FAD) only accounts for 1 per cent of all cases and is known to be entirely inherited. FAD is passed directly from one generation to another through a dominant gene. If a parent has FAD each child has a 50 per cent chance of inheriting AD.

Genetic risk factors in late onset Alzheimer's disease (AD): In late onset AD certain genes appear to influence a person's vulnerability in developing the disease. The gene responsible for such disease is the Apolipoprotein E gene. This gene occurs in three forms in humans: types 2, 3, and 4. All of us carry two Apolipoprotein genes: they can be the same type (2,2; 3,3; or 4,4) or a mixture of two types (2,3; 2,4; 3,4). It has been found that people with at least one type 4 are at increased risk of developing AD earlier in life than those with the other types of Apolipoprotein E. People with type 2 (especially 2,2) appear to be protected against developing Alzheimer's disease, until much later in life.

Down's syndrome: Most people with Down's syndrome, who live long enough to reach late adulthood, may be at a risk of developing AD. Read more about Alzheimer's disease are you at risk?

You might also like to read:

• 6 movies portraying Alzheimer's disease
• What every dementia or Alzheimer's caregiver ought to know
• 'Alzheimer's is no more an old age condition'
• Early medical help can slow effects of disease

With inputs from IANS

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