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Frequent loss of heterozygosity (LOH) on the long arm of chromosome 17 has been described in breast tumor DNAs by a number of groups, and recent fine genetic mapping and cloning of an inherited breast-ovarian cancer susceptibility locus (BRCA1) to a small region of 17q12-q21 has focused interest on this area. The absence of sporadic mutations in the BRCA1 gene in breast tumors studied so far suggests that there may be other tumor suppressor genes in the region involved in sporadic breast cancer. We studied 28 sporadic breast cancers with 14 highly polymorphic markers on chromosome 17 (2 on 17p and 12 on 17q). Most of the 17q markers are located within the 17q12-q23 region. We confirmed that 50% of tumors have deletions of at least one locus on chromosome arm 17q, and that half the deleted cases probably correspond to monosomies 17 or 17q. The other half correspond to a partial deletion on 17q and were used to identify 2 smallest common deleted regions (SCDR1 and SCDR2) on 17q12-q23. SCDR1 comprised the THRA1 gene, but not the 2 flanking loci tested (D17S250 and D17S800); while SCDR2 was defined by loci GIP and GH. BRCA1 was deleted in half the cases but it is outside the SCDR1. Moreover, breast tumors in young women frequently showed chromosome 17 alterations.

Hereditary, non-polyposis colon cancer (HNPCC) is caused by mutations in different loci. One gene causing HNPCC was mapped to chromosome 2p and recently a tight linkage between a polymorphic marker on the chromosome 3p and the disease locus has been demonstrated and these families also manifest signs of a general DNA replicator disorder. We report detailed genetic studies of three French HNPCC families with D2S123 and D3S1029. In one of the families (F 230), the segregation pattern for markers on chromosomes 2 and 3 suggests absence of linkage. The two other families are not informative enough to conclude on linkage status with chromosomes 2 and 3. If confirmed, this result would mean that the inherited colon cancer in this family is linked to another HNPCC gene. Implication for genetic counselling is discussed. Even with cloned genes, linkage analysis with flanking microsatellite markers for informative families may help to avoid tedious work of seeking point mutations in HNPCC genes.

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant disease, accounting for approximately 6% of colorectal cancers. We performed linkage analyses with the aim of proving or excluding the existence of a susceptibility locus on 17q. Three HNPCC families (102 collected members, 25 colorectal cancers, 9 other cancers and 6 colorectal adenomas) were studied with 7 polymorphic DNA markers Mfd15, THRA 1, D17S800, D17S855, Mfd 188, 42D6, 46E6 localized in the 17q11-q23 region. After in vitro enzymatic amplification, the different alleles were separated by classic vertical poly-acrylamide gel electrophoresis or analyzed with the automatic sequencing machine 373A (Applied Biosystems). Results showed that none of the 7 studied markers of the chromosome 17q were linked to the HNPCC disease.