Alzheimer's disease. Computer artwork showing amyloid proteins on brain tissue (grey). Alzheimer's is a neurodegenerative disease and a common cause of dementia in the elderly. It is caused by the build-up of amyloid proteins in the brain, which form plaques. Microglial cells, which normally digest dead nerve cells and pathogens, are activated by these plaques and secrete substances that cause the brain's nerve cells to die. Patients with Alzheimer's disease have progressive memory loss, impaired intellect, loss of co-ordination and a continuous decline in the ability to perform daily tasks. The cause of the condition is not known and there is no cure, although some drugs can alleviate some of the symptoms.