People with AD are more likely to have an APOE e4 allele than people who do not develop AD.

FORBES: Gene Tests For Everyone

However, many people with AD do not have an APOE e4 allele.

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The work is evidence of a phenomenon called paramutation, in which orders issued by a version of a gene (an allele, in the jargon) in one generation are remembered in subsequent generations, even if the allele itself has not been inherited.

ECONOMIST: Mice inherit more than just DNA