Reliability of self-reported ancestry among siblings: implications for genetic association studies.

This study investigated the reliability of self-reported ancestry by comparing the interview responses of probands and their siblings. A total of 546 sibling pairs were ascertained in a family-based study of susceptibility genes for Parkinson's disease and asked to identify maternal and paternal countries of origin. Probands were recruited prospectively from the Department of Neurology of the Mayo Clinic in Rochester, Minnesota, from June 1, 1996, through May 31, 2005. Probands resided within Minnesota or one of the four surrounding states (Wisconsin, Iowa, South Dakota, North Dakota). Only 49 percent of these sibling pairs, primarily Caucasian, agreed completely on the countries of origin of both parents. The agreement increased to 68 percent when named countries were postcoded into six population genetic clusters (as previously defined by microsatellite markers). Self-reported ancestry may not be a reliable method to reduce the possible impact of population stratification in genetic association studies of outbred populations, such as in the United States.