A polygenic risk score accurately predicted cerebral amyloid angiopathy (CAA) in 105 participants, achieving 78% predictive accuracy for this condition where amyloid proteins accumulate in brain blood vessels rather than brain tissue itself. The genetic test maintained strong performance even in individuals with high overall amyloid burden, suggesting it can distinguish between different patterns of amyloid deposition. This genetic approach addresses a critical gap in Alzheimer's treatment as new amyloid-clearing drugs enter clinical use. CAA significantly increases risk of brain bleeding and swelling during amyloid-targeting therapy, making patient identification crucial for treatment safety. Current MRI-based detection often misses early CAA, but this polygenic score showed promise even in MRI-negative cases. The finding represents an important advance in precision medicine for neurodegeneration, potentially enabling clinicians to stratify patients by bleeding risk before initiating amyloid therapies. However, the relatively small validation cohort and need for autopsy confirmation to establish ground truth limit immediate clinical application. Larger prospective studies comparing genetic prediction to clinical outcomes will determine whether this approach can meaningfully improve treatment decisions in Alzheimer's disease management.