What is Alzheimer’s disease?
Alzheimer’s disease is a neurodegenerative disease which is characterised by loss of neurons and synapses in the brain, called cerebral atrophy. It affects around 6% of people over the age of 65 and is the leading cause of dementia.
What is the difference between Alzheimer’s and dementia?
Dementia is a general term for age related cognitive decline, whereas Alzheimer’s is a specific neurological condition. Alzheimer’s accounts for 40-60% of all instances of dementia, and is often referred to as Alzheimer’s dementia. Other types of dementia include:
- Vascular dementia
- Lewy-body dementia
- Frontotemporal dementia
- Mixed dementia
How does Alzheimer’s Disease work?
It isn’t very well understood how Alzheimer’s disease originates, and there are multiple competing theories, but we do know how it affects the brain. There are two main biological markers:
Neurofibrillary tangles are misfolded “tau” proteins that collect inside neurons. Healthy neurons have support systems called microtubules, which help guide nutrients and molecules from the cell body to outer parts of the neuron, such as the axon and dendrites. In healthy neurons, tau normally binds to and stabilizes microtubules. In Alzheimer’s disease, abnormal chemical changes cause tau to detach from microtubules and stick to other tau molecules, forming tangles inside neurons. These tangles block the microtubules from transporting molecules along the neuron, which harms the communication between neurons.
What’s the result?
Cerebral
atrophy
Both the Aβ plaques and the neurofibrillary tangles disrupt communication between neurons. If neurons can’t communicate between each other, programmed cell death takes place, in which the neuron’s will deem themselves not useful and die off. This causes cerebral atrophy which means reduction of brain matter.
Restricted
blood flow
A second issue that arises from these abnormalities includes constriction of cerebral blood flow (CBF). This can be caused by Aβ plaques blocking arteries, atherosclerosis (hardening of arteries) and increased risk of stroke. People with Alzheimer’s typically have around 20% lower volumes of blood in the brain than those with healthy brains. Restriction of blood flow around the brain means that vital molecules like oxygen and various nutrients are not as effectively distributed.
Chronic
inflammation
Finally, people with Alzheimer’s often experience chronic inflammation of the brain. This is likely due to the buildup of glial cells which are trying to repair the damage done by the Aβ plaques and neurofibrillary tangles. Among other roles, glial cells support brain health by destroying pathogens and removing dead neurons. The sudden increase in dead neurons (from the programmed cell death) mean that glial cells intended to remove them build up and cause inflammation in the brain, a side effect which can cause further damage.
What can be done to stop this?
There is currently no cure for Alzheimer’s, but there are treatments available in the UK .to ease symptoms and either slow, pause, or temporarily improve cognitive decline.