Twenty microsatellite loci on chromosome 9 were analysed for allelic l
osses 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 heterozygo
sity (LOH) affecting 9p was observed in melanoma DNAs from 18 individu
als (72%). Observations of losses of identical alleles in different me
tastatic lesions from the same patients, and of LOH in a vertical grow
th phase primary melanoma, were consistent with previous reports of ch
romosome 9 deletion early in melanoma development. LOH data suggested
the loss of entire copies of chromosome 9 in 11 cases, and the termina
l deletion of all or a portion of 9p in six cases. A somatic interstit
ial deletion of 9p between D9S162 and D9S169 was seen in a familial me
lanoma. This 21 cM deleted region corresponded with the previously rep
orted positions of homozygous deletions in melanoma cell lines, and of
the familial melanoma susceptibility locus (MLM). As 16 of the 18 cas
es 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 r
ole in the development of most sporadic melanomas.