Aims

Donepezil (acetylcholinesterase inhibitor) is an approved drug for the symptomatic treatment of Alzheimer’s disease (AD). However, inconsistent results have been reported across clinical trials, which might be explained by the biological heterogeneity in AD. A new model describing biological subtypes has opened an opportunity to understand this heterogeneity by combining two dimensions, severity and typicality [1]. Here, we investigated the impact of this subtyping model on the response to donepezil in patients with suspected prodromal AD.

Methods

The effects of donepezil were investigated in 173 MCI individuals (donepezil=83; placebo=90) with structural MRI data at both baseline and follow-up (6-12-month). Efficacy outcomes were the annualized percentage change (APC) of the volumes in the hippocampus, ventricles, total grey matter, and the AD cortical thickness signature. Patients were classified as typical-AD, limbic-predominant, hippocampal-sparing, or minimal atrophy, based on visual ratings. Complementary, the two core dimensions for subtyping were analyzed as continuums using an index of global brain atrophy for severity and the hippocampus-to-cortex ratio for typicality.

Results

Among patients classified as minimal atrophy or hippocampal sparing, those treated with donepezil showed a slower atrophy rate than their subtype-specific placebo group.

Both the severity and typicality dimensions independently modulated donepezil efficacy, especially in AD-related regions. In general, patients showing a lower degree of atrophy and/or hippocampal atrophy responded better to treatment.

Conclusions

Biologically defined subtypes are useful to target patients more accurately for the treatment with donepezil. Positioning patients along subtyping dimensions could provide meaningful information regarding their prognosis and response to treatment.