Alzheimer’s disease is a chronic progressive neuro-degenerative disorder characterised by three primary groups of symptoms. The first group (cognitive dysfunction) includes memory loss, language difficulties, and executive dysfunction (that is, loss of higher level planning and intellectual coordination skills). The second group comprises psychiatric symptoms and behavioural disturbances — for example, depression, hallucinations, delusions, agitation — collectively termed non-cognitive symptoms. The third group comprises difficulties with performing activities of daily living (deemed “instrumental” for more complex activities such as driving and shopping and “basic” for dressing and eating unaided)."

Source : BMJ 2009;338:b15

Alzheimer’s (abbreviated as AD) is the most common cause of dementia, with an estimated 30 million sufferers worldwide at any one time. The cause of Alzheimer’s disease is unknown.

For many years, it was thought that the 'amyloid plaques' (buildup of abnormal peptide proteins) which form in the brains of AD sufferers, was a primary cause of the dementia. It's now thought more likely that the plaques are as a result of the disease, or even that they are a protective agent which forms due to natural defence responses by brain neurons.

Note that recently approved drugs (e.g. Lecanemab) which can help slow the buildup of the plaques, don't appear to be very effective in halting the progress of the disease itself.

Current opinion is leaning towards the idea that AD might be triggered by an infectious agent of some kind - perhaps a virus or a bacterium. Various candidate organisms are being investigated, including the Epstein Barr virus, the herpes simplex virus 1 (present in around 70% of the population), and bacteria which cause gum disease. At present, no infectious agent has definitely been identified as a cause.

See Nature, news feature, Nov. 2020

Further information Alzheimer's Society, UK

Also see : Vascular dementiaplugin-autotooltip__plain plugin-autotooltip_bigVascular dementia

"Vascular dementia (VD) is the second most common cause of dementia following Alzheimer’s disease (AD). The major symptoms of VD including memory loss, language deficits and impairment of executive functions. Its specific etiology and pathogenesis remain unknown. and Neurofibrillary tanglesplugin-autotooltip__plain plugin-autotooltip_bigNeurofibrillary tangles

Neurofibrillary tangles (which are technically described as 'aggregates of hyperphosphorylated tau protein') are commonly known as a primary marker of Alzheimer's disease. They are also prevalent in numerous other diseases - generally known as

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