Linkage and association analysis of nevus density and the region containing the melanoma gene CDKN2A in UK twins

Rare mutations in the CDKN2A gene are highly penetrant for melanoma. Density of nevi is under strong genetic control and high density is a potent risk factor for melanoma. We used linkage and association analysis in adolescent twins from the UK to examine the hypothesis that the region containing the CDKN2A gene also contains a quantitative trait locus influencing normal nevus development. Five markers in the CDKN2A region were genotyped in 115 dizygotic twin pairs, and one marker (D9S942) was genotyped in 103 monozygotic twin pairs, all of whom had been phenotyped for nevus density. Linkage analysis showed no evidence of a quantitative trait locus influencing nevus density in this chromosomal region. A model partitioning the variation in phenotype into within- and between-twin pair components showed weak evidence of association between higher nevus density and longer mean length of the two D9S942 alleles (P = 0.01). This relation, which was also observed in an earlier Australian twin study, could be because of the linkage disequilibrium between D9S942 and a neighbouring functional locus. Further investigation of this region is warranted in large-scale linkage or association studies.