Comparisons Of Two Large Long-Term Studies In Alzheimer’s Disease

The incidence of Alzheimer’s disease (AD), the leading cause of dementia, is predicted to increase at least three fold by 2050. Curing this disease is a global priority. Currently, two major studies are attempting to gain further understanding of this disease; the Alzheimer’s Disease Neuroimaging Initiative (ADNI) and the Australian Imaging, Biomarker and Lifestyle Study (AIBL). We describe these two cohorts to assess the impact of combining them to provide a larger cohort for analyses.

An initial comparison of the protocols was carried out and recruitment strategies were shown to be marginally different between the studies. Inclusion criteria specified ages between 55 and 90 years in ADNI and >65 years in AIBL. Marginally different specifications for disease stage classifications of healthy controls (HC), mild cognitively impaired (MCI) and AD individuals were observed, for example, different Mini-Mental State Exam (MMSE) cut-offs. However, both studies had AD diagnosis supported by the NINDS/ARDA criteria. Baseline characteristics were compared between ADNI and AIBL cohorts. Overall, AIBL had more HCs compared to ADNI (69% vs 30%), but fewer MCI individuals (12% vs 50%). The ADNI cohort had a higher level of education and generally, within a disease classification, there were minimal differences in baseline age, sex, MMSE, and Preclinical Alzheimer Cognitive Composite (PACC) scores.

Longitudinal analyses compared the change over time for the two cohorts and disease classifications for PACC and MMSE. There were no significant differences in cohorts within the HC and MCI groups, but within the AD group, subjects in the ADNI cohort had generally higher predicted PACC and MMSE scores over time than those in AIBL.

Our results suggest there is the potential to combine the ADNI and AIBL cohorts for analysis purposes to provide one more powerful data set; however, consideration should be taken for some measures.