If some brain cells are killed by viral infection or damaged in another way, it will probably trigger a similar cascade as in post-polio syndrome. The post-polio syndrome is gradually worsening and often after a long time. Compared to men, larger cell mosaic in women, and especially in people with Down’s syndrome, may explain why these groups are more exposed to both conditions than men. Even if a possible viral infection of brain cells did not kill them, the infected cells will probably be perceived as different from uninfected cells and increase the cell mosaic and the forgetfulness.
Since TT virus infection is detected in many people and in some cases has been detected in the brain, the virus is a possible candidate.
We do not know the cause of Alzheimer’s disease, but it occurs earlier in people with Down’s syndrome. Therefore, it is possible that increased cell mosaic predisposes. If an association also contains a mosaic of more than two cell types in humans with Down’s syndrome, it is assumed that the associations must be extra-large for being remembered well.
But if Alzheimer’s disease is caused by a virus, it is likely that such an infection in the brain of a patient with Down’s syndrome fast would increase the tendency of the associations to be forgotten since then the cell mosaic will increase further.
Also the expected renewal of glia cells from the bone marrow may fail, and if so, the working memory will suffer first.