Hereditary prostate cancer in Finland: fine-mapping validates 3p26 as a major predisposition locus.

In a recent genome-wide linkage (GWL) analysis of Finnish families at high risk for prostate cancer, we found two novel putative susceptibility loci at 3p25-p26 and 11q14. Here, we report the fine-mapping of these two critical regions at high resolution with 39 microsatellite markers in 16 families, including multiplex families that were not used in the GWL scan. The maximum multipoint HLOD was 3.39 at 3p26 and 1.42 at 11q14. The highest LOD scores were seen around markers D3S1270 and D3S4559 (alpha=0.89), covering approximately two megabases. The two known genes in this region CHL1 (cell adhesion molecule with homology to L1CAM) and CNTN6 (contactin 6) were screened for exonic mutations in the families showing the strongest linkage, but no disease-segregating sequence variants were observed. The recombination map pointed to a region proximal to the area of best linkage, suggesting that more genes may need to be investigated as candidates. These results provide strong evidence for the existence of a prostate cancer susceptibility gene at 3p26 in Finnish prostate cancer families. This locus has not been strongly linked with hereditary prostate cancer in other populations. However, the mildly positive 3p LOD scores in a recent GWL analysis of patients from the United States suggest that the locus may also be important in other populations.

Genome-wide scanning for linkage in Finnish breast cancer families.

Only a proportion of breast cancer families has germline mutations in the BRCA1 or BRCA2 genes, suggesting the presence of additional susceptibility genes. Finding such genes by linkage analysis has turned out to be difficult due to the genetic heterogeneity of the disease, phenocopies and incomplete penetrance of the mutations. Isolated populations may be helpful in reducing the level of genetic heterogeneity and in providing useful starting points for further genetic analyses. Here, we report results from a genome-wide linkage analysis of 14 high-risk breast cancer families from Finland. These families tested negative for BRCA1 and BRCA2 germline mutations and showed no linkage to the 13q21 region, recently proposed as an additional susceptibility locus. Suggestive linkage was seen at marker D2S364 (2q32) with a parametric two-point LOD score of 1.61 (theta=0), and an LOD score of 2.49 in nonparametric analyses. Additional genotyping of a 40 cM chromosomal region surrounding the region of interest yielded a maximum parametric two-point LOD score of 1.80 (theta=0) at D2S2262 and a nonparametric LOD score of 3.11 at an adjacent novel marker 11291M1 in BAC RP11-67G7. A nonparametric multipoint LOD score of 3.20 was seen at 11291M1 under the assumption of dominant inheritance. While not providing proof of linkage considering the small number of families and large number of laboratory and statistical analyses performed, these results warrant further studies of the 2q32 chromosomal region as a candidate breast cancer susceptibility locus. Both linkage and association studies are likely to be useful, particularly in other isolated populations.