Transmission-ratio distortion in the Framingham Heart Study

Transmission-ratio distortion (TRD) is a phenomenon in which the segregation of alleles does not obey Mendel's laws. As a simple example, a recessive locus that results in fetal lethality will result in live-born individuals sharing more alleles at this locus than expected under Mendel's laws. This could result in apparent linkage of the phenotype of 'being alive' to such a chromosomal regions. Further, this could result in false-positive linkage when 'affected-only' parametric or non-parametric linkage analysis is performed. Similarly, loci demonstrating TRD may be detectable in family-based association tests as deviant transmission of alleles. Therefore, TRD could result in confounding of family-based association studies of diseases. The Framingham Heart Study data available for Genetic Analysis Workshop 16 is a suitable dataset to determine whether there are loci in the genome that reveal TRD because of the large number of individuals from families, the high-resolution genotyping, and the population-based nature of the study. We have used both genome-wide linkage and family-based association methods to determine whether there are loci that demonstrate TRD in the Framingham Heart Study. Family-based association analysis identified thousands of loci with apparent TRD. However, the vast majority of these are likely the result of genotyping errors with application of strict quality control criteria to the genotype data, and automated inspection of the intensity plots, we identify a small number of loci that may show true TRD, including rs1000548 in intron 6 of S-antigen (arrestin, SAG) on chromosome 2 (p = 7 x 10-10).