A second enzyme, Gamma-secretase, also snips APP in another place. These released fragments are thought to benefit neurons. In Alzheimer's disease, the first cut is made most often by another enzyme, Beta-secretase. That, combined with the cut made by Gamma-secretase, results in the release of short fragments of APP called Beta-Amyloid. When these fragments clump together, they become toxic and interfere with the function of neurons. As more fragments are added, these oligomers increase in size and become insoluable, eventually forming Beta-Amyloid plaques. Neurofibrillary tangles are made when a protein called tau is modified. In normal brain cells, tau stabilizes structures critical to the cell's internal transport system. Nutrients and other cellular cargo are carried up and down the structures called microtubules to all parts of the neuron. In Alzheimer's disease, abnormal tau separates from the microtubules, causing them to fall apart. Strands of this tau combine to form tangles inside the neuron, disabling the transport system and destroying the cell. Neurons in certain brain regions disconnect from each other and eventually die, causing memory loss. As these processes continue, the brain shrinks and loses function. We now know a great deal about changes that take place in the brain with Alzheimer's disease, but there is still much to learn. What other changes are taking place in the aging brain and its cells and what influence do other diseases, genetics, and lifestyle factors have on the risk of developing Alzheimer's disease as the brain and body age? Scientific research is helping to unravel the mystery of Alzheimer's and related brain disorders As we learn more, researchers move ever closer to discovering ways to treat and ulimately prevent this devestating, fatal disease.