Prior to the multipoint linkage analysis, we fitted a polygenic model and estimated the heritability of age at onset to be 11.8% ± 3.9% (P < 0.001). The random environmental effects thus contributed 88.2% of the total variation for this trait. The distributions of the highest multipoint LOD scores (logarithm of the odds to the base 10) and their corresponding chromosome positions for each of the genetic marker sets are presented in Table 1 and Figure 1 for selected chromosomes. The highest LOD score obtained with microsatellites was 1.43 on chromosome 1 at 243 cM (on marker D1S549), with none of the other chromosomes having LOD score greater than 1.00. For the SNPs, the highest LOD scores were 1.95 at 159 cM on chromosome 7 for Illumina, and 1.80 at 230 cM on chromosome 1 for Affymetrix. Other chromosomes with highest LOD scores above 1.00 include 4, 16, 18, and 21 for both Illumina and Affymetrix SNPs; and chromosomes 3 and 9 for Affymetrix SNPs. The distributions of the highest linkage signals on the chromosomes are generally similar for both
