Chromosome 21 (AD1)

Research of chromosome 21 is involved for the form of AD known as Early Onset Familial (FAD) which is the result of an autosomal dominant mutation. FAD can strike early (in one's 50's) and often, in some families and is sometimes considered a separate form of the disease. There seems to be an abnormality on chromosome 21 that is common in a few of the families with a history of FAD. This chromosome contains the gene for the amyloid precursor protein (APP). This type of mutation is rare and only found in a few of these families though. Also there is a region on chromosome 14 that is common in a larger population of these families. The gene on chromosome 21 carries the code for an abnormal form of APP, the parent protein for beta-amyloid, called S182. This is suspected to be responsible for a majority of the early onset cases, though the form is still considered rare. This supports the theory that beta-amyloid plays a central role in some forms of AD, although it has been found only in about 5 percent of the early-onset FAD families.

The gene on chromosome 21 in the gene involved in Down's Syndrome. Down's Syndrome is similar to AD in the respect that people with Down's Syndrome have an extra version of chromosome 21, and those who live to 30 or 40, usually develop plaques and tangles like those found in AD and develop similar symptoms. Compared to the chromosome gene, the gene on chromosome 14 occurs more often in people with FAD. This gene is in the process of being tracked down among the 10,000 or so DNA bases in this region alone.

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