Neurofibrillary tangles are found inside the brain cells of people with Alzheimer’s disease. They are one of the distinctive features of Alzheimer’s, together with accumulations of protein known as amyloid plaques. At a microscopic level, a neurofibrillary tangle is seen to consist of a bundle of thread-like structures called microtubules. These are tangled together with proteins known as tau proteins. Tau proteins and microtubules occur normally within brain cells, but in people without Alzheimer’s most of the microtubules are parallel to one another and the tau proteins link them together in an orderly way.
Alzheimer’s disease is the most frequent cause of dementia, where there is a slow decline in brain function. It is a common illness, affecting millions of people worldwide, and there is no cure. The brains of people with Alzheimer’s appear shrunken compared with those of healthy individuals, and the spaces, or ventricles, within the brain are larger. Inside the nerve cells of the brain, the classic sign of Alzheimer’s is the presence of neurofibrillary tangles and amyloid plaques, or senile plaques. Senile plaques consist of a collection of protein found outside nerve cells in the brain, and although they exist in healthy elderly people they are found in much greater numbers in Alzheimer’s patients.
Inside a healthy nerve cell in the brain, microtubules are arranged in straight rows. They serve as a structural framework for the cell, as well as a transport network along which substances can pass. Tau proteins form part of connecting structures which hold the microtubules together.
In Alzheimer’s disease, the tau proteins become deformed and can no longer help support the orderly arrangement of microtubules, with the result that the transport network is disrupted. Nerve cells may no longer communicate effectively, and it is thought the inability to transport substances could also contribute to their death later in the disease. It is possible to see neurofibrillary tangles in the brain of a person without Alzheimer’s, because they do occur in healthy individuals, but in much smaller numbers.
As cells normally have efficient mechanisms for getting rid of faulty proteins, it is not known why in Alzheimer’s disease the brain cell does not dispose of the deformed tau proteins found inside a neurofibrillary tangle. Ongoing research into the function of various proteins involved in removing damaged tau may help to develop a cure for Alzheimer’s in the future. As yet, there are no existing treatments which are able to eradicate senile plaques and neurofibrillary tangles, but drugs are available which may slow progression of the disease for some people.