Dr. Risch, a statistical geneticist, genetic epidemiologist, and population geneticist is involved in a variety of projects of both a theoretical and applied nature. These studies include both clinical and population genetic projects. He has developed novel tools and approaches for the mapping and identification of genetic variants underlying both Mendelian and non-Mendelian diseases. For example, he contributed to the cloning of genes for torsion dystonia and hemochromatosis. He defined admixture mapping in ethnically admixed populations as a tool for gene discovery and has applied it to such diseases as hypertension and lipidemia. In collaboration with his colleague Kathleen Merikangas, he proposed genome-wide association studies as the next generation tool after linkage analysis for identifying novel disease susceptibility variants; this approach, now applied on a large scale, has identified thousands of novel disease and trait-related genetic variants. Over the past decade, Dr. Risch has collaborated with colleagues at Kaiser Permanente Northern California Division of Research (where he holds an adjunct appointment) to develop a large cohort combining electronic health record information with environmental and genomic data for genetic epidemiology research related to aging. The cohort contains approximately 110,000 individuals with genome-wide genotype and telomere length data, and has been the basis for a variety of genetic studies related to cardiovascular, metabolic and cancer outcomes. He is also currently active in genetic epidemiologic studies of autism spectrum disorder, utilizing a large cohort of affected families identified through state of California record linkage databases. In the realm of population genetics, he has characterized the role of ancestry in mate selection and its impact on genetic patterns of linkage disequilibrium in the population over time. He has developed novel methods for estimating kinship in admixed populations, and also described methods of admixture analysis in populations which have undergone significant genetic drift, such as the Ashkenazi Jewish population.