LINE-1 methylation in peripheral blood and the risk of melanoma in melanoma-prone families with and without CDKN2A mutations

Cutaneous malignant melanoma (CMM) is an etiologically heterogenous disease with genetic, environmental (sun exposure), and host (pigmentation/nevi) factors and their interactions contributing to risk. Recently, epigenetic changes involving reduced levels of global DNA methylation in blood have been associated with genomic instability and cancer risk. We thus examined whether global methylation was associated with CMM risk in individuals from melanoma-prone families with and without CDKN2A germline mutations. We measured global DNA methylation using bisulfite pyrosequencing at four CpG sites of the long interspersed nucleotide element-1 (LINE-1) sequences in peripheral blood mononuclear cells (PBMCs) from individuals in 64 melanoma-prone families including 114 CMM cases (45 CDKN2A-positive and 69 CDKN2A-negative) and 121 unaffected individuals (31 CDKN2A-positive and 90 CDKN2A-negative). We used unconditional logistic regression to evaluate the association between CMM status and LINE-1 methylation levels, adjusting for age at blood draw and accounting for familial correlation in the variance. We found that male sex was significantly associated with higher overall LINE-1 methylation (P=0.0001). However, the overall and site-specific levels of LINE-1 methylation did not vary significantly by CMM status (overall odds ratio: 1.57, 95% confidence interval: 0.84-2.95, P=0.16; comparing lowest to highest or reference methylation group). Similar results were obtained when CDKN2A-positive and CDKN2A-negative families were analyzed separately. Our findings did not support a significant association between constitutional LINE-1 methylation in PBMCs and risk of CMM in melanoma-prone families with or without CDKN2A mutations.