These tangles seem to consistently present in specific locales of neurons. These include projection neurons in defined cytoarchitectural fields within the hippocampus and association cortices, while other neurons in the sensory and motor cortex are spared. The tangles consist primarily of a microtubule associated protein, tau This protein is normally only located in axonal projections. In Alzheimer and Down s patients tan appears in the somatodendritic compartment within neurofibrillar tangles. As the proteins build up and are phosphorylated, the cell eventually dies.
Senile plaques demonstrate a similarity to tangles in their topographic hierarchical distribution.
Dr. Masters has demonstrated Beta A-4 protein is present in normal individuals by the age of 45, and increases with age. Eighty percent of the population over 80 years of age show significant amounts of amyloid protein. Down s patients, however, begin to manifest this plaque precursor nearly thirty years earlier. Current investigations are attempting to determine if this amyloid protein is causally related to the formation of neurofibrillar tangles. Evidence is not yet conclusive.