Family history information on essential tremor: Potential biases related to the source of the cases

The proportion of essential tremor (ET) cases that can be attributed to gen etic factors is unknown: estimates range from 17-100%. One possible reason for this variability is that clinic and community cases may differ with reg ard to family history of ET. This is because clinic patients are self-selec ted and represent as few as 0.5% of all ET cases. Our goal was to determine whether ET cases ascertained from a clinic differed from those ascertained from a community in terms of the family history information that they prov ided. Subjects (57 clinic. 64 community) underwent a family history intervi ew. Clinic cases were 4.73 times more likely to report an affected relative than were community cases. We conclude that there was a substantial differ ence between our clinic and community ET cases in terms of the information they provided regarding their family history. Selection and reporting biase s could have accounted for this difference. Because of these biases, the so urce of the cases must be taken into consideration when investigators are t rying to synthesize the widely variable results of studies that have estima ted the genetic contribution to ET. (C) 2001 Movement Disorder Society.