The illness is chronic mercury toxicity and the treatment is chelation therapy. I know a man who reversed his dementia with chelation therapy. He's an older guy that would get lost in his own neighborhood.
Steven Fowkes, a chemist, has done a lot of work in presenting the some of the latest research regarding Alzheimer's and how it relates to mercury toxicity. A good start is his Quora answer here: https://www.quora.com/Why-havent-we-made-progress-in-a-cure-...
Some other good scientific literature is the work of Boyd Hayley with the chelator emeramide. He's in the process of getting it approved through the FDA for treatment of acute mercury toxicity. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3346673/ https://www.ncbi.nlm.nih.gov/pubmed/29444690?dopt=Abstract