Cases in Precision Medicine: The Role of Pharmacogenetics in Precision Prescribing

Cases in Precision Medicine: Genetic Testing to Predict Future Risk for Disease in a Healthy Patient

Genetic testing is performed more routinely in clinical practice, and direct-to-consumer tests are widely available. It has obvious appeal as a preventive health measure. Clinicians and their healthy patients increasingly inquire about genetic testing as a tool for predicting diseases, such as cancer, heart disease, or dementia. Despite demonstrated utility for diagnosis in the setting of many diseases, genetic testing still has many limitations as a predictive tool for healthy persons. This article uses a hypothetical case to review key considerations for predictive genetic testing.

Defining Clinical Utility of Tumor Biomarker Tests: A Clinician's Viewpoint

Tumor biomarker tests (TBTs) are used to guide therapeutic strategies for patients with cancer. However, the regulatory environment for TBTs in the United States is inconsistent and, in general, TBTs are poorly valued. The National Academy of Medicine has recommended that TBTs should not be used in general practice until they are shown to have analytical validity and clinical utility. The latter term, first coined by the Evaluation of Genomic Applications in Practice and Prevention Initiative, has been widely stated but is indeterminately defined. In considering whether a TBT has clinical utility, several factors need to be considered: (1) What is the intended use of the TBT? (2) What are the end points that are used to determine clinical utility? (3) How substantial does the difference in end points between groups defined by the TBT need to be to determine therapeutic strategies? (4) What is the risk tolerance of the stakeholders? and (5) Who are the stakeholders that make the decision? For all these factors, the data used to consider clinical utility must be derived from level I evidence studies. In conclusion, there is no strict definition of clinical utility for a TBT. However, consideration of these factors will lead to more objective conclusions. Doing so will facilitate value-based decisions regarding whether a TBT should be used to guide patient care.

Evaluating the current level of pharmacists' pharmacogenomics knowledge and its impact on pharmacogenomics implementation

The pharmacists' role is potentially vital in the growing field of personalized medicine, and well-defined guidelines and knowledge that support this role need to be established. To address the knowledge gap, over the past two decades, pharmacy schools have started providing pharmacogenomics-related courses, a field that overlaps with pharmacy and personalized medicine. Given the fact that pharmacists lead 50% of the Clinical Pharmacogenetics Implementation Consortium implementers' sites, their role can be particularly crucial to move forward the integration of precision medicine in clinical practice. Herein, we aim to identify the educational challenges for pharmacogenomics integration into clinical practice and their impact on pharmacists' knowledge and confidence, in addition to underscoring pharmacists' role in pharmacogenomics as a whole.

Association of interleukin-6 gene polymorphisms and glaucoma: Systematic review and meta-analysis

AIM

To conduct a systematic review and meta-analysis to explore the association between IL-6 gene polymorphisms (rs1800795 and rs1524107) and glaucoma.

METHODS

A comprehensive search was performed to select eligible studies regarding IL-6 polymorphisms and glaucoma. The effect sizes in the fixed-effects model were calculated using odds ratios (ORs) with 95% confidence intervals (CIs).

RESULTS

Four eligible studies comprising 762 cases and 799 controls were selected for meta-analysis. Regarding the association between the IL-6 rs1800795 polymorphism and glaucoma, those who carried the G/G+G/C genotypes had a non-significant higher risk of glaucoma (OR = 1.29, 95% CI = 0.76-2.19) in the dominant model. However, no obvious association (OR = 0.97, 95% CI = 0.68-1.37) was found for the recessive model (G/G vs G/C+C/C). In the subgroup analysis stratified by ethnicity, no significant associations were observed in populations of Asian or European heritage. Significantly higher glaucoma risks of 15.9 and 99.0 were observed for the dominant (C/C+C/T vs T/T) and recessive (C/C vs C/T+T/T) models, respectively.

CONCLUSION

No statistically significant glaucoma risks were observed for the rs1800795 except rs1524107 polymorphism of IL-6. Further studies with a larger sample size are required to validate the effects of IL-6 polymorphisms on glaucoma risk.

Toward precision prescribing for methadone: Determinants of methadone deposition

BACKGROUND

Despite the World Health Organization listing methadone as an essential medication, effective dose selection is challenging, especially in racial and ethnic minority populations. Subtherapeutic doses can result in withdrawal symptoms while supratherapeutic doses can result in overdose and death. Although CYP3A4 was conventionally considered the principal methadone metabolizing enzyme, more recent data have identified CYP2B6 as the principal enzyme. CYP2B6 has ethnically-associated polymorphisms that affect the metabolic rate. Our objective was to investigate the effects of genetic and nongenetic factors on methadone metabolism.

METHODS

We measured trough plasma methadone levels in 100 participants with opioid use disorder. We assessed methadone metabolism by calculating the metabolite ratio (major metabolite: 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine [EDDP] divided by methadone concentration). We assessed hepatic fibrosis and steatosis by transient elastography and CYP2B6 alleles, principally responsible for methadone metabolism. Mixed effects models modeled the data in 97 participants.

RESULTS

Participants were largely male (58%), minority (61% African American) and non-Hispanic (68%). Forty percent were HCV mono-infected, 40% were uninfected, and 20% were HCV/HIV co-infected. Female sex had significant effects on (R)- and (S)-methadone metabolism (p = 0.016 and p = 0.044, respectively). CYP2B6 loss of function (LOF) alleles significantly affected (S)-methadone metabolism (p = 0.012). Body mass index (BMI) significantly affected (R)-methadone metabolism (p = 0.034). Methadone metabolism appeared to be lower in males, in individuals with LOF alleles, and elevated BMI.

CONCLUSIONS

Genetic analysis, especially in minority populations, is essential to delivering individualized treatments. Although the principal methadone metabolizing enzyme remains controversial, our results suggest that sex, CYP2B6 genotype, and BMI should be incorporated into multivariate models to create methadone dosing algorithms. Methadone dosing algorithms should facilitate medication delivery, improve patient satisfaction, and diminish overdose potential.