I guess the Alzheimer's Society UK also doesn't know what they are talking about... I did not say that all dementia was hereditary, I said there is scientific evidence that SOME dementia can be hereditary. It's no different than having any other gene abnormality in your family, some people might get the gene mutation that predisposes them to some sort of disease but may never develop it while others will be stricken with the illness. The opinion of one Scientist or Doctor is not definitive proof of anything. To quote a good friend of mine, who is a Neurosurgeon, "It's called Practicing Medicine for a reason."
https://www.alzheimers.org.uk/info/20010/risk_factors_and_prevention/117/genetics_of_dementia