New Alzheimer's Disease Risk Factor: TREM2

Triggering Receptor Expressed on Myeloid cells 2 protein.  TREM2.  Kind of rolls off the tongue, doesn't it?  Hmmm . . . maybe not.  Well, we better start getting used it, along with amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2), all of which are involved in familial early-onset Alzheimer's disease as well as the better known e4 allele of apoliprotein E (ApoE) which is involved in late-onset Alzheimer's disease.  Why?  Because 2 articles were published online earlier this week in the New England Journal of Medicine in which the authors linked late-onset AD to variations in TREM2 based upon genetic sequencing.

Now before you rush off to your family physician and ask him/her to order up a test from deCODE (cute, huh?), stop for a minute.  One study was based upon 2,261 Icelanders which showed that a rare mutation was associated with almost 3x risk of developing AD.  At any given age from 80-100yo, those genetic carriers of this rare mutation had worse cognitive function than those who did not carry the mutation.  The authors then looked for and found this genetic mutation in American, German & Dutch cohorts with the same degree of risk of developing AD.

In the second study, the authors compared the prevalence of a TREM2 mutation in 1,092 participants w/AD compared to 1,107 controls.  They then compared another 1,887 cases with 4,061 controls.  It should be noted that participants from the United Kingdom, Portugal, Canada & United States were involved in this analysis.

So we've got 2 strong studies linking a genetic mutation to an increased risk of developing late-onset AD.  But as I teach my residents, just because you can do a test or procedure doesn't mean that you should do so.  Before you ask your family physician to order that test, ask yourself what you'll do with that additional bit of information.  If the results are negative, will you sit back & relax, forgetting that nutrition & exercise have also been strongly linked to other dementias, especially vascular.  If the results are positive, will you become depressed & suicidal?  Or become anxious, even super-vigilant, every time you forget something because you were distracted?  How will this affect your daily life (and that of your family's)?  At least the Affordable Care Act will ensure your future insurability in light of this newly discovered pre-existing condition, right?

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