The effect of hormone therapy on olfactory sensitivity is dependent on apolipoprotein E genotype

Patients with Alzheimer's disease (AD) show a deficit in olfactory threshold sensitivity. The Apolipoprotein E (ApoE) ɛ4 allele is associated with increased risk of AD and earlier symptom onset. Hormone therapy (HT) may exert neuroprotective effects on brain areas affected by AD. The current study investigated the effect of HT on performance on an olfactory threshold test in ɛ4 positive and ɛ4 negative non-hysterectomized, non-demented, elderly females and AD patients. Among the non-demented participants, ɛ4 positive females who had received HT performed 1) significantly better than those without HT, and 2) at levels similar to those of ɛ4 negative females. In contrast, those without HT who were ɛ4 positive performed significantly worse than those who were ɛ4 negative. HT had no effect on performance in AD patients regardless of ɛ4 status. These results suggest that HT may offer protection against loss of olfactory function in ɛ4 positive individuals in preclinical stages of AD. Future research is warranted in order to investigate further the neuroprotective role of HT on sensory and cognitive functions in non-demented aging individuals.