Identifying influential individuals in linkage analysis: Application to a quantitative trait locus detected in the COGA data

Once linkage is detected to a quantitative trait locus (QTL), the next step towards localizing the gene involved may be to identify those families, or individuals, in whom the putative mutations are segregating. In this paper , we describe a jackknife procedure for identifying individuals (and famili es) who contribute disproportionately to the linkage. Following initial det ection of linkage to a QTL, the strategy involves sequentially removing eac h individual (or each family) from the analysis and recomputing the lod sco re associated with the linked region using data from all remaining subjects (or families). This procedure can be used to determine if particular obser vations have substantial impact on evidence for linkage. Identification of such observations may provide insights for further efforts to localize the QTL. (C) 1999 Wiley-Liss, Inc.