Alzheimer's+Causes

=**What Are The Causes of Alzheimer’s disease?**= ====Many experiments have been performed to determine the biological and genetic causes of Alzheimer’s. Alzheimer’s disease is inherited through genetic DNA variations known as single-nucleotide polymorphisms (SNPs). A polymorphism is a variation in a gene to express different phenotypes (physical characteristics). These SNPs are variations in DNA, which are located on the coding regions of DNA called exons. Exons are the regions in DNA that determine all the physical traits and genes that an individual expresses. If these exons are changed at all, then it could cause serious defects in the making of proteins from the genes coded in the exon. On the RNA sequence, which is what codes DNA, there are exons along with introns. These introns are non-coding regions and are removed through splicing. Once the introns are removed, the exons undergo transcription, which is the process that makes the template for protein synthesis. Not every part of the exons code for amino acids, but the SNPs that occur in the exons can affect the nearest genes in the sequence.====

====The SNPs that are related to AD deal with the genes that regulate cholesterol and lipid processing and inflammatory pathways. One gene that is affected is ApoE, which is a major cholesterol carrier that regulates lipid transport and repairs brain injuries. There are three different alleles (variations) of ApoE; ε4, ε3, and ε2 and each allele carries it own amount of risk in whether or not an individual will develop AD. The ε3 allele is the most common allele connected with AD, but if an individual has the ε4 allele, they have an increased risk of AD and if an individual has ε2, the risk of AD is decreased. The ε4 allele is also known to increase the risk for disease of the blood vesicles in the brain, which causes poor blood circulation in the brain and a decline in cognition.====

====Amyloid-β peptide (Aβ) is formed from the cleavage (splitting) of the amyloid precursor protein (APP) two enzymes β-secretase and γ-secretase. APP is located in many tissues and in concentrated in neuron synapses. It has been found that APP binds to cholesterol, which makes up the myelin surrounding the neurons in the brain (Chen et al., 2013). Myelin is needed around the neurons in order for the synapses to occur. The more myelin there is around the neuron, the faster the signal is sent. If APP is cleaved, it is no longer able to function properly and bind to cholesterol and form myelin. This results in the amount of myelin around the neuron to diminish.====

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