We did not discover any additional linkage peaks in the gender- stratified analyses. The chromosome 3 linkage peak was somewhat stronger in the FO group (Overall maximum LOD score of 2.77 in Category 5) than in the MC group (Overall maximum LOD score of 1.85 in Category 4), whereas the chromosome 9 linkage peak showed a greater difference in the opposite direction (Overall maximum LOD scores of 3.62 in MC Category 8 and 1.30 in FO Category 9, though the disparity may be explained by the greater number of MC than FO sibships in Categories 8 and 9). The subgroup characteristics are given in Table S1, and the complete nonparametric linkage data for the Total group and all four subgroups are provided in Text S1, S2, S3, S4 and S5.

The parametric analysis generally supported the results of the nonparametric analysis, showing all four linkage peaks in their respective groups and categories to be robust to different assumptions about the mode of inheritance. The chromosome 3 peak produced a higher maximum hLOD score under a recessive model (4.652) than a dominant model (3.334), whereas the

The only previous genomewide linkage scan for exceptional longevity used a minimum actual age at death or last contact of 98 for probands and 91 or 95 for additional male or female siblings,

Lop         2 [Total —Previous —New —MC —FO       2 [=Total —Previous —New —MC —FO        Total —Previous —New —MC —FO    A   2 [=Total —Previous —New —MC —FO  

somes 3, 9, 12, and 4 linkage peaks. LOD scores for the entire chromosome are plotted for the Category that produced the highest LOD score in the Total group for chromosomes 3 and 9, and the highest LOD score in the New and Previous subgroups for chromosomes 12 and 4, respectively. A) Chromosome 3, Category 4. B) Chromosome 9, Category 8. C) Chromosome 12, Category 6. D) Chromosome 4, Category 3.

The previous study produced distinct linkage peaks at both the 3p24-22 and 9q31-34 loci reported here, but with relatively small LOD scores of about 0.8 and 1.0, respectively. Our corresponding Overall maximum LOD scores for the two peaks in the Previous subgroup were 4.49 and 3.43 in Categories 5 and 8, but the scores in Category 1 were only 3.22 and 0.18. The chromosome 12 linkage peak reported here only in the New subgroup was completely absent from the previous study. Therefore, compared to the previous scan the discovery of the three novel loci was probably most attributable to different factors in each case: the increased informativity of the 10K marker panel for chromosome 3, the use of a range of age cutoffs for chromosome 9, and the expansion of our sample set for chromosome 12. Other previous scans using age-related traits have provided some evidence for linkage to chromosome 3p [25,27], but given the disparate phenotypes and coarse microsatellite maps in these studies, it is difficult to assess the relevance of their data to our results.

panels [54] and larger sample sizes, but detection of loci with small effects and gene identification require other methods [55]. An association study of genes under the previously reported chromosome 4q22-25 linkage peak [24] implicated a SNP in the promoter of MTTP (MIM 157147) as associated with longevity [28], but multiple attempts to replicate this result were unsuccessful [12,26,28,56-58]. It has been suggested that these studies also cast doubt on the prior linkage evidence [59], when in fact the two issues are largely independent, and this study was the first adequately powered attempt to replicate the previous scan. Although we were unable to reproduce the chromosome 4 linkage in the Total group or independent New subgroup, the evidence was stronger when only sibships used in the original study were analyzed (Overall maximum LOD score of 2.20 in Previous Category 3), indicating heterogeneity between subgroups. Impor- tantly, only 129 of the 137 original sibships were available for this study, which could help account for the failure of our LOD score in Previous Category 1 (2.14) to reach the LOD score of 3.65 reported previously [24]. However, the Maximum LOD Score (MLS) statistic [60,61] with the possible triangle constraint [62], as implemented by GeneHunter [33] in the original report [24], was later documented to result in a slight anticonservative bias that was most pronounced in small sample sizes [34]. The Kong and Cox LOD score [32] used here was not subject to that bias [34], possibly indicating the LOD score from the previous scan was somewhat inflated relative to our scan.

       Total —Previous —New —MC —FO        Total —Previous —New —MC —FO  

Several candidate genes in the linkage peaks discussed here warrant mention. The gene TOP2B (MIM 126431) in the chromosome 3 linkage peak encodes an isozyme of topoisomerase II, which is potently inhibited by resveratrol and related compounds from grape cell culture [63]. Resveratrol can mimic the effects of caloric restriction, mitigate the symptoms of age- related diseases, and/or extend lifespan in a variety of model organisms, including mammals [64,65]. Various human topo- isomerase homologs have also been shown to regulate cellular senescence [66,67], promote telomere stability [68], and interact

Table 2. Characteristics of chromosomes 3, 9, 12, and 4 linkage peaks.