Another cause of severe memory loss, particularly affecting people over 80 years of age, has been found. So the known causes of the disorders called dementia are now believed to be: Alzheimer’s disease, Vascular dementia, Dementia with Lewy bodies, ‘LATE’ (the newly understood cause) and, importantly various mixtures of these brain disorders.
You can read about it in a CNN post:
https://edition.cnn.com/2019/04/30/health/dementia-late-alzheimers-study/index.html
or in detail in an article in the journal Brain.