Clustering and Additive Effects of Nongenetic Risk Factors in Non–Autosomal-Dominant Degenerative and Vascular Young Onset Dementia

INTRODUCTION: Both genetic and nongenetic factors contribute to the risk profile of young onset dementia (YOD), but risk factors often co-occur. This matched case-control study examined whether nongenetic risk factors cluster together, to inform targeted prevention efforts. METHODS: Ninety-six participants with non-autosomal-dominant degenerative and/or vascular YOD and 175 controls were recruited to 2 Australian epidemiological studies. Risk exposure was retrospectively self-reported and/or informant-reported. RESULTS: Each additional exposure increased the risk for YOD, though only where vascular dementia was included in the analysis. Cluster analysis identified 4 risk groups, one of which reported a high probability of exposure to all risks and a significantly higher risk for YOD. DISCUSSION: Results suggest that combinations of nongenetic risk factors confer more risk for young onset vascular dementia, and possibly primary degenerative YOD, than a single factor on its own. Compared with their same-age peers, some people with YOD experience a lifetime of risk exposure starting from early in life.