Genomewide Study of Epigenetic Biomarkers of Opioid Dependence in European- American Women

Abstract

There is currently an epidemic of opioid use, overdose, and dependence in the United States. Although opioid dependence (OD) is more prevalent in men, opioid relapse and fatal opioid overdoses have recently increased at a higher rate among women. Epigenetic mechanisms have been implicated in the etiology of OD, though most studies to date have used candidate gene approaches. We conducted the first epigenome-wide association study (EWAS) of OD in a sample of 220 European-American (EA) women (140 OD cases, 80 opioid-exposed controls). DNA was derived from whole blood samples and EWAS was implemented using the Illumina Infinium HumanMethylationEPIC array. To identify differentially methylated CpG sites, we performed an association analysis adjusting for age, estimates of cell proportions, smoking status, and the first three principal components to correct for population stratification. After correction for multiple testing, association analysis identified three genome-wide significant differentially methylated CpG sites mapping to the PARG, RERE, and CFAP77 genes. These genes are involved in chromatin remodeling, DNA binding, cell survival, and cell projection. Previous genome-wide association studies have identified RERE risk variants in association with psychiatric disorders and educational attainment. DNA methylation age in the peripheral blood did not differ between OD subjects and opioid-exposed controls. Our findings implicate epigenetic mechanisms in OD and, if replicated, identify possible novel peripheral biomarkers of OD that could inform the prevention and treatment of the disorder.

Figure 1

Manhattan plot. The Manhattan plot depicts the association between DNA methylation and opioid dependence (OD) in European American (EA) women (n = 220). The horizontal dotted line represents the genome-wide significant (GWS) threshold of p < 5.9 × 10⁻⁸.

Figure 2

Violin plots of genome-wide significant (GWS) CpG sites associated with opioid dependence (OD). DNA methylation levels (beta values) of GWS CpG sites associated with OD are shown: (A) cg17426237 (PARG gene), (B) cg21381136 (RERE gene), and (C) cg18177613 (CFAP77 gene) in opioid-exposed controls and OD cases. All CpG sites showed hypomethylation associated with OD. ^*Represents GWS threshold of p < 5.9 × 10⁻⁸.

Figure 3

Association between genotype data at rs2611513 and DNA methylation levels at GWS CpG site cg17426237. rs2611513 associated with DNA methylation levels at cg17426237; C allele associated with lower DNA methylation in (A) all sample (n = 141, p = 0.025), and (B) OD cases (n = 112; p = 0.042). No association was obtained in (C) opioid-exposed controls (n = 29; NS). ^*Represents p < 0.05.

Figure 4

Association between genome-wide significant (GWS) CpG sites and opioid dependence (OD)-related traits. DNA methylation (beta values) of GWS CpG sites associated with OD-related traits are shown: (A–C) OD symptoms, (D–F) age of onset (years), (G–I) duration of opioid use (years), (J–L) longest duration of chronic opioid use (years). Significant threshold is set at p < 0.05.