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Four genes involved in the development of Alzheimer disease have been identified.Three fully penetrant(deterministic)genes lead to the development of Alzheimer disease in patients younger than 60 years:the amyloid B-protein precursor on chromosome 21,presenilin 1 on chromosome 14,and presenilin 2 on chromosome 1.Together,they account for about half of this early-onset form of the disease.One genetic risk factor-- apolipoprotein E-4--is associated with late-onset Alzheimer disease.It accounts for a substantial fraction of disease burden but seems to act primarily to lower the age of disease onset.In general,none of these genes can be easily adapted for use as a diagnostic or predictive test for Alzheimer disease.Research activity includes searching for additional genes,especially for late-onset disease,and elucidating the mechanism of action of all identified genes as part of a long-term effort to develop more effective therapeutic and preventive strategies. |
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