Sib-pair linkage analyses of nuclear family data: quantitative versus dichotomous disease classification.

Model-free sib-pair linkage analysis was used to screen 367 highly polymorphic markers for evidence of linkage to a disease, defined either quantitatively (Q1) or dichotomously (AF). Five individual replicates, plus a case family data set containing all families in these replicates with at least one individual with AF, were analyzed. Sib-pair linkage results for Q1 and AF varied considerably among the five replicates and did not consistently detect any of the three underlying major loci, MG1, MG2, and MG3. For the pooled case families, linkage analyses of Q1, but not AF, detected the flanking markers for MG1 and MG2 at the 0.05 and 0.01 levels, respectively. Overall, type 1 error rates were not elevated. The ability to analyze the disease quantitatively (Q1) and construct a data set more appropriate for linkage analysis (case families) enhanced the power to detect at least some of the major loci underlying the disease.