Table 1.

Causes of Alzheimer Disease

Cause% of Cases
Late-onset familial 1 (age >60-65 years)15%-25%
Early-onset familial 1 (age <60-65 years)<2%
Down syndrome 2<1%
Unknown (includes genetic/environment interactions)~75%
1.

≥3 persons in a family with AD

2.

Essentially all persons with Down syndrome (trisomy 21) develop the neuropathologic hallmarks of AD after age 40 years [McCarron et al 2017]. If carefully observed or tested, more than half of individuals with DS also show clinical evidence of cognitive decline. The presumed reason for this association is the lifelong overexpression of APP on chromosome 21 encoding the amyloid precursor protein and the resultant overproduction of β-amyloid in the brains of persons who are trisomic for this gene.

From: Alzheimer Disease Overview

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