<prompt> Biochemical aetiology of Alzheimers disease relates toSerotoninDopamineAcetylcholineGABA  <response>: Alzheimers disease is the commonest cause of dementia and it is not treatable disorder. Neurochemically there is a marked decrease in the brain choline acetyltransferase CAT with a similar decrease in brain acetylcholinesteraseAchE Ref: a sho textbook of psychiatry, Niraj Ahuja, 7th edition, pg no.24. The main neurotransmitter implicated in Alzheimers disease is Acetylcholine. 