What is being tested?This test looks for
mutations in the PSEN1 gene, which have been associated with Early Onset Familial
Alzheimer’s Disease (EOFAD, also called Alzheimer's Disease Type 3 or AD3). Although most AD starts after the age of 65 (late onset), about 5-10% of cases of the disease begin in people under 65 years of age. Much of this early onset AD is familial - it runs in family lines and is caused by a genetic mutation. There have been three
genes identified so far that are associated with AD3; all are very rare. Of these, PSEN1 is the most common and is thought to cause about half the cases of AD3.
Since PSEN1 is a dominant gene, it only takes one mutated copy, inherited from either your mother or father, to cause AD3. Why PSEN1 is associated with AD3 is not yet known. The normal role of the PSEN1 gene and the function of presenilin 1, the
protein it produces, are being studied but are still not fully understood; however, it appears to be an enzyme involved in breaking down the protein found in the Alzheimer’s disease
plaques. PSEN1 is a rare mutation. So far, about 40 mutations of the PSEN1 gene have been identified but only in about 50 different family lines worldwide.
The PSEN1 genetic mutation analysis is new and not widely accepted yet. In its present form, it is only capable of identifying about 30-60% of patients who have AD3 caused by a PSEN1 mutation. The analysis is made easier if a patient already has an identified PSEN1 mutation in their family line.
