Dementia accompanies aging in certain susceptible individuals. The chemical function of the brain remains normal, but certain neurotransmitter-selective diseases, such as Parkinson's disease, Huntington's disease, and Alzheimer's disease occur more commonly with age.There are at least two issues troubling researchers of senile dementia at the moment. One is the contribution of cell death, as opposed to selective neuronal atrophy, to the pathology of degenerative disorders. The other is how early the onset of dementia might be detected. The resolution of such (...) issues is important for the design of therapies for the common and most serious chronic, rather than acute, neurodegenerative disease.Alzheimer's disease is one of the most devastating neurological disorders. The ethical debate is often related to when human biological life ceases or when a person ceases to exist. If the elder is still a person, he/she is no more the same person. Huntington's disease is inherited as a highly penetrant, autosomal dominant neuronal disorder. A genetic test can accurately predict a person's risk and that of the children. As the knowledge of the genetic basis is increasing and prenatal diagnosis gets easier, the possibilities to avoid child disorders will become greater, but genetic testing raises problematic ethical issues. Ethical action involves the right to know and the right not to know, it involves freedom of choice and freedom implies knowledge. It is ethical that relatives in age of procreation should be informed. In any case, efficacy and safety of the procedure, the risk-benefit ratio for a particular disease must be judged to be acceptable and understood through informed consent by the patient or the family or both. (shrink)