Background: Dementia with Lewy bodies (DLB) is a complex, progressive neurodegenerative disease with considerable phenotypic, pathological, and genetic heterogeneity. Objective: We tested if genetic variants in part explain the heterogeneity in DLB. Methods: We tested the effects of variants previously associated with DLB (near APOE, GBA, and SNCA) and polygenic risk scores for Alzheimer's disease (AD-PRS) and Parkinson's disease (PD-PRS). We studied 190 probable DLB patients from the Alzheimer's dementia cohort and compared them to 2,552 control subjects. The p-tau/Aβ1-42 ratio in cerebrospinal fluid was used as in vivo proxy to separate DLB cases into DLB with concomitant AD pathology (DLB-AD) or DLB without AD (DLB-pure). We studied the clinical measures age, Mini-Mental State Examination (MMSE), and the presence of core symptoms at diagnosis and disease duration. Results: We found that all studied genetic factors significantly associated with DLB risk (all-DLB). Second, we stratified the DLB patients by the presence of concomitant AD pathology and found that APOE ϵ4 and the AD-PRS associated specifically with DLB-AD, but less with DLB-pure. In addition, the GBA p.E365K variant showed strong associated with DLB-pure and less with DLB-AD. Last, we studied the clinical measures and found that APOE ϵ4 associated with reduced MMSE, higher odds to have fluctuations and a shorter disease duration. In addition, the GBA p.E365K variant reduced the age at onset by 5.7 years, but the other variants and the PRS did not associate with clinical features. Conclusion: These finding increase our understanding of the pathological and clinical heterogeneity in DLB.