Chromosome 9 deletion in sporadic and familial melanomas in vivo

Twenty microsatellite loci on chromosome 9 were analysed for allelic losses in DNAs from 30 uncultured melanomas from 25 patients, relative to DNA from autologous peripheral blood lymphocytes. All patients were constitutionally heterozygous at several loci, and loss of heterozygosity (LOH) affecting 9p was observed in melanoma DNAs from 18 individuals (72%). Observations of losses of identical alleles in different metastatic lesions from the same patients, and of LOH in a vertical growth phase primary melanoma, were consistent with previous reports of chromosome 9 deletion early in melanoma development. LOH data suggested the loss of entire copies of chromosome 9 in 11 cases, and the terminal deletion of all or a portion of 9p in six cases. A somatic interstitial deletion of 9p between D9S162 and D9S169 was seen in a familial melanoma. This 21 cM deleted region corresponded with the previously reported positions of homozygous deletions in melanoma cell lines, and of the familial melanoma susceptibility locus (MLM). As 16 of the 18 cases of 9p LOH in the present study were observed in individuals with no family history of melanoma, it is likely that the MLM locus plays a role in the development of most sporadic melanomas.