<prompt> All are true statements about Alzheimers disease except:Downs syndrome association is protectiveNeural plaques containing Ab amyloid are seenHippocampus is severely affected10 patients develop Capgras syndrome  <response>: A Downs syndrome association is protective Pathogenesis of Alzheimers disease: Earliest metabolic change occur in prenatal cortex but most severe lesion seen in hippocampus, temporal cortex and nucleus basalis of myernest Lateral septur. Important microscopic findings : Senile plaques an cytoplasmic neurofibrillary tangles NFTs. Neuritic plaque contain : AfJ amyloid, proteoglycans, ApoE, antichymotrypsin, and other proteins. NFTs are silver-staining, twisted neurofilaments in neuronal cytoplasm that represent abnormally phosphorylated tau t protein and appear as paired helical filaments by electron microscopy. Tauis microtubule associated protein that may function to assemble and stabilize microtubules that convey cell organelles, glycoproteins and other important materials through neuron. Phosphorylation of tau protein may disturb normal process. Cerebral cortical level of Ach, CAT and nicotinic cholinergic receptors. Genetic factors : Mutation on APP gene located on chromosome 21 Mutation in presenelins 12 located on chromosome 1 14 respectively. ApoE gene is on chromosome no. 21. ApoE is involved in cholesterol transport. The e4 allele of ApoE genes shows strong association with AD. The ApoE e4 allele specially in homozygous state 44 is an important risk factor for AD. 