Provided herein is a method for identifying a genetic variant that is associated with development of a condition of interest (e.g., Alzheimer's disease), and genetic variants so identified. Methods of treatment with an active agent (e.g., with a particular active agent and/or at an earlier age) is also provided, upon detecting a genetic variant described herein. In some embodiments, the genetic variant is a deletion/insertion polymorphism (DIP) of the TOMM40 gene. Kits for determining if a subject is at increased risk of developing late onset Alzheimer's disease is also provided. Kits for determining if a subject is responsive to treatment for a condition of interest with an active agent are further provided.