APOE and early-onset autosomal dominant Alzheimer disease: This notion is supported by genome-wide association studies (GWASs), which have (i) identified shared risk loci across neurodegenerative diseases, such as APOE and BIN1 in Alzheimer’s disease (AD) and Lewy body dementia (LBD), or GBA, SNCA, TMEM175 in Parkinson’s disease (PD) and LBD and (ii) demonstrated that genetic risk scores derived from one neurodegenerative disease can predict risk of another, as with AD and PD scores predicting risk of LBD3–5.