Other hypotheses
Retrogenesis is a medical hypothesis that just as the fetus goes through a process of neurodevelopment beginning with neurulation and ending with myelination, the brains of people with Alzheimer's disease go through a reverse neurodegeneration process starting with demyelination and death of axons (white matter) and ending with the death of grey matter.[73] Likewise the hypothesis is, that as infants go through states of cognitive development, people with Alzheimer's disease go through the reverse process of progressive cognitive impairment.[74]

The association with celiac disease is unclear, with a 2019 study finding no increase in dementia overall in those with CD, while a 2018 review found an association with several types of dementia including Alzheimer's disease.[75][76]

According to one theory, dysfunction of oligodendrocytes and their associated myelin during aging contributes to axon damage, which in turn generates in amyloid production and tau hyper-phosphorylation.[77][78]

Studies have shown a potential link between infection with certain viruses and developing Alzheimer's disease later in life.[79] Notably, a large scale study conducted on 6,245,282 patients has shown an increased risk of developing Alzheimer's disease following COVID-19 infection in cognitively normal individuals over 65.[80]