Background: Opioid use disorder (OUD) has been an increasing concern in Canada as mortality rates continue to rise. Though OUD treatments, such as methadone maintenance treatment (MMT), reduce its burden, they could potentially cause harm due to OUD’s variance in severity and presentation across individuals. It is hypothesized that genetic variants such as single nucleotide polymorphisms (SNPs) could predispose patients to respond differently to MMT. In addition, sex differences have been observed in opioid use patterns, treatment outcomes, and genetic make-up. As such, this thesis aims to identify significant SNPs associated with treatment outcomes in genome-wide association studies, and test biologically relevant SNPs with MMT outcomes of interest, while highlighting sex differences. This is achieved through a systematic review protocol, a systematic review, and a candidate gene study.
Methods: A protocol was prepared for the planning of the first ever systematic review of genome-wide significant findings of medication-assisted treatment outcomes for OUD patients. The systematic review assessed the literature findings and study qualities, narratively summarizing significant associations. Next, a candidate gene study analyzed the association between SNPs in OPRM1 and CYP2B6 genes, and continued opioid use, relapse, and methadone dose within an ancestrally European sample (n=1226). Sex-stratified and sex-interaction analyses were also conducted.
Results: The systematic review included 5 studies and qualitatively assessed 43 unique genetic variants. The candidate gene study showed no significant associations between the selected OPRM1 and CYP2B6 SNPs and outcomes of interest. While no significant differences between the sexes were observed, rs73568641 and rs3745274 showed near significance associations in only one sex, females, and males, respectively.
Discussion: Through the study of genetic variants associated with treatment outcomes in the literature and our sample of ancestrally European individuals on MMT, we were able to highlight gaps in pharmacogenetics research and identify areas of focus for future studies. / Thesis / Master of Science (MSc) / Recently, opioid use disorder (OUD) has been declared a national crisis in Canada. OUD treatments are helpful in reducing opioid use and adverse events. However, their dosing and metabolism in patients can impact continued opioid use, relapse, or treatment dose changes. Due to the variability in response between individuals, there might be a genetic basis to treatment outcomes. This thesis explores which genetic variants reported in previous studies are involved in OUD treatment outcomes. Then, it tests select genetic variants in OPRM1 and CYP2B6 genes to see if they are linked to specific outcomes in an Ontario population and tries to identify if these associations differ by sex. No significant associations were found, though associations in males and females had near-significant results in one sex but not the other. Despite suggesting sex’s possible involvement in treatment outcomes, more research is necessary to confirm these findings.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/25929 |
| Date | January 2020 |
| Creators | Chawar, Caroul |
| Contributors | Samaan, Zainab, Neuroscience |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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