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Odor Identification: Marker for Early Alzheimer Disease?

Odor Identification: Marker for Early Alzheimer Disease?

  • Presymptomatic signs of Alzheimer Disease (AD): Subtle cognitive changes, CSF biomarkers, MRI and PET findings[1]
    More convenient markers needed to intervene early and slow AD progression
    Odor identification (OI) impaired in aging and dementia
       Rhinoencephalic brain region especially vulnerable to AD pathology
       OI may be a potential biomarker for presymptomatic AD

  • Cross-sectional study of OI as biomarker of presymptomatic AD
    274 healthy individuals ≥60 years
       Parent or multiple siblings with AD
       Seen at McGill University (Montreal)
    AD biomarkers measured in 101 CSF donors: total tau, phospho-tau, and their ratios with Alzheimer β-amyloid
    OI tested with standardized scratch and sniff booklets

  • Overall unadjusted results showed impaired OI linked to:
       Lower cognitive score (P<.02)
       Older age (p<.02)
    Increased ratios of total tau and phospho-tau to β-amyloid (p < 0.02)
    OI known to be impaired in aging and dementia, link between OI, age and cognition expected

  • Analyses restricted to CSF donors:
       Results adjusted for age, cognition, APOE Ɛ4, education, and sex
       Links between impaired OI, older age and lower cognition disappeared
       Link between impaired OI and total tau/β-amyloid remained (p=0.005)
    Suggests impaired OI may be an early indicator of AD pathology before symptom onset

  • OI test may be affected by nasal congestion
    High percentage of women with high levels of education, results may not generalize
    CSF puncture by volunteer, may introduce bias
    Small sample, cross-sectional design:  cannot determine if results reflect change over time
       Longitudinal studies in progress

  • “While impaired OI may in fact help identify persons who could for various reasons eventually have cognitive impairment, we strongly urge that our present cross-sectional results not be regarded as rationale for clinical use of olfactory testing as an AD diagnostic. We suggest, however, that OI may serve for research purposes as a simple and inexpensive indicator of evolving AD pathology. Indeed, we are exploring its use as a biomarker in clinical trials among asymptomatic persons at risk of later dementia symptoms,” lead author John C.S. Breitner, MD, MPH. for the PREVENT-AD Research Group (McGill, University, Montreal)

  • Small Canadian study in healthy aging individuals at high risk for AD found decreased OI was linked to increased CSF biomarkers of AD pathology, after adjusting for important confounders.
    Impaired OI may be a simple, inexpensive biomarker of early AD pathology in the research setting.
    Longitudinal studies evaluating OI as a biomarker in asymptomatic individuals at risk for AD are ongoing.

  • Reference
    1. Lafaille-Magnan ME, Poirier J, Etienne P, et al. Odor identification as a biomarker of preclinical AD in older adults at risk. Neurology. 2017;89(4):327-335.

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