Background: Approximately 10% of human cutaneous melanomas occur in families in which several members are affected. The familial predisposition to this disease is often associated with dysplastic nevus syndrome, a condition in which afflicted family members have multiple dysplastic nevi (atypical moles). The chromosome region 9p21 and markers on chromosomes 1p and 6p have been linked to melanoma susceptibility. The tumor suppressor genes CDKN2A and CDKN2B have been mapped to the 9p21 region, and genetic analyses have revealed the presence of germline CDKN2A alterations in melanoma families. The reported frequencies of such alterations, however, vary among these families.
Purpose: The present investigation was carried out to determine the frequencies of CDKN2A and CDKN2B germline gene mutations among members in a population-based cohort of Swedish melanoma families (i.e., melanoma kindreds).
Methods: DNA was prepared from blood samples obtained from 181 individuals belonging to 100 melanoma kindreds. The polymerase chain reaction (PCR) technique, followed by single-strand conformation polymorphism (SSCP) and nucleotide sequence analyses, were used to identify the types and frequencies of mutations in exons 1, 1beta, 2, and 3 of the CDKN2A gene and in exons 1 and 2 of the CDKN2B gene.
Results: CDKN2A gene aberrations were independently identified by both SSCP and nucleotide-sequence analyses. Nucleotide-sequence analysis identified a single point mutation leading to a substitution of leucine for proline in codon 48 of exon 1 in a family with a history of melanoma and several other cancers. A second abnormality, leading to an insertion of an extra arginine residue at codon number 113 of exon 2, was seen in four separate families. The CDKN2A exon-3 coding region had the wild-type sequence in all samples. No germline mutations were found in the alternative exon 1beta of the CDKN2A gene or in exons 1 and 2 of the CDKN2B gene.
Conclusions: The present investigation demonstrates that CDKN2A germline gene mutations were observed in 7.8% of the 64 Swedish melanoma kindreds that each included at least two first-degree relatives with melanoma and dysplastic nevus syndrome. No CDKN2A exon 1beta or CDKN2B mutations were identified. The critical genes responsible for the inheritance of a susceptibility to develop melanoma among family members in this population have yet to be identified.