Clinical Pharmacogenetic Testing and Application: Laboratory Medicine Clinical Practice Guidelines

Pharmacogenomic Considerations for Anticoagulant Prescription in Patients with Hereditary Haemorrhagic Telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is a vascular dysplasia that commonly results in bleeding but with frequent indications for therapeutic anticoagulation. Our aims were to advance the understanding of drug-specific intolerance and evaluate if there was an indication for pharmacogenomic testing. Genes encoding proteins involved in the absorption, distribution, metabolism, and excretion of warfarin, heparin, and direct oral anticoagulants (DOACs) apixaban, rivaroxaban, edoxaban, and dabigatran were identified and examined. Linkage disequilibrium with HHT genes was excluded, before variants within these genes were examined following whole genome sequencing of general and HHT populations. The 44 genes identified included 5/17 actionable pharmacogenes with guidelines. The 76,156 participants in the Genome Aggregation Database v3.1.2 had 28,446 variants, including 9668 missense substitutions and 1076 predicted loss-of-function (frameshift, nonsense, and consensus splice site) variants, i.e., approximately 1 in 7.9 individuals had a missense substitution, and 1 in 71 had a loss-of-function variant. Focusing on the 17 genes relevant to usually preferred DOACs, similar variant profiles were identified in HHT patients. With HHT patients at particular risk of haemorrhage when undergoing anticoagulant treatment, we explore how pre-emptive pharmacogenomic testing, alongside HHT gene testing, may prove beneficial in reducing the risk of bleeding and conclude that HHT patients are well placed to be at the vanguard of personalised prescribing.

The efficacy of clopidogrel in preventing recurrent cardiovascular events among Arab population carrying different CYP2C19 mutations: systematic review and meta-analysis

Background

The prevalence and the role of CYP2C19 gene mutations concerning recurrent Cardiovascular Events (CVEs) among patients treated with clopidogrel is still controversial especially among Arab people. Therefore, this review aimed to determine the frequency of CYP2C19 polymorphic alleles among the Arab population and to investigate the efficacy of clopidogrel as an antiplatelet drug among those carrying different variants of this gene.

Methodology

Two authors independently searched in PubMed, Google Scholar, and EMBASE databases at any year for studies related to the role of CYP2C19 gene on the prognosis of patients with CVEs treated with clopidogrel. The review included Arab people who were genotyped to determine the frequency of CYP2C19 genotypes and alleles (the qualitative part). Concerning the quantitative part (meta-analysis), only patients who previously had CVEs and using clopidogrel as secondary prophylaxis had been included. The Newcastle Ottawa Scale for non-randomizes Studies was utilized to consider the risk of bias among included studies. We analyzed the data using odds ratio at 95% confidence interval and the quality of evidence of each outcome measure was judged using GRADE approach.

Results

The current study revealed that 4% of Arabs reported in the included studies are homozygous, and 25% are heterozygous for the CYP2C19*2 allele. While 3% and 18.5% of them are homozygous and heterozygous of CYP2C19*17 alleles, respectively. A significant increased risk of recurrent CVEs by about threefold was associated with CYP2C19*2 or CYP2C19*3 allele carriers (OR = 3.32, CI = 1.94–5.67, and OR = 3.53, CI = 1.17–10.63, respectively). However, no significant increased risk among carriers of CYP2C19*17 mutation (OR = 0.80, (CI = 0.44–1.44) was documented.

Conclusion

The present study revealed that Arabs carrying CYP2C19*2 and CYP2C19*3 alleles could be at increased risk of decreasing the antiplatelet efficacy of clopidogrel and an alternative drug should be prescribed for those patients to avoid recurrent CVEs. However, few available studies were included in the quantitative part of the analysis and further studies with large sample size are recommended to confirm our results.

Analytical validation of a laboratory-development multigene pharmacogenetic assay

OBJECTIVE

The implementation of pharmacogenetics (PGx) in clinical practice is an essential tool for personalized medicine. However, clinical laboratories must validate their procedures before being used to perform PGx studies in patients, in order to confirm that they are adequate for the intended purposes.

METHODS

We designed a validation process for our in-house pharmacogenetic PCR-based method assay.

RESULTS

The concordance to reference, repeatability and reproducibility was 100%. Sensitivity and specificity were 100% for the detection of variant diplotypes in CYP2C9, CYP3A5, TPMT, DPYD and UGT1A1 genes. The sensitivity was lower in the detection of CYP2C19 variants due to a limitation in the design that prevents the detection of CYP2C19 *2/*10 diplotype.

CONCLUSIONS

The success of implementing clinical pharmacogenetic testing into routine clinical practice is dependent on the precision of genotyping. Limitations must be bearing in mind to guarantee the quality of PGx assays in clinical laboratory practice. We provided objective evidence that the necessary requirements in our laboratory-development assay were fulfilled.

Polymorphisms of genes related to phase-I metabolic enzymes affecting the clinical efficacy and safety of clopidogrel treatment

Introduction: Clopidogrel is an antiplatelet medication described as a prodrug, which cannot exert the antiplatelet effect until being biotransformed to the active metabolite. It is commonly used to reduce the risk of blood coagulation in patients diagnosed with acute coronary syndrome, or ischemic stroke.Area covered: We reviewed published articles in PubMed and Google Scholar that focused on the mutations of CYP2C19, CYP3A4, CYP2C9, CYP2B6, and CYP1A2 genes related to clopidogrel clinical efficacy and safety.Expert opinion: Based on current pharmacogenetic studies, patients carrying CYP2C19*2, CYP2C19*3, CYP2C9*3, and CYP2B6*5 alleles may not respond to clopidogrel due to poor platelet inhibition efficacy revealed among them. In contrast, carriers of CYP2C19*17, CYP3A4*1G, and CYP1A2*1C alleles showed a more significant antiplatelet effect in clopidogrel users and expected to have a protective role as a genetic factor against cardiovascular events. Genotyping for either CYP2C19, CYP3A4, CYP2C9, CYP2B6, or CYP1A2 variants is not recommended when considering clopidogrel treatment for patients, as some trials showed specific non-genetic factors (e.g. age and diabetes) that could affect clopidogrel responsiveness. Instead, platelets inhibition tests could be used as predictors of the clinical efficacy of clopidogrel treatment. Other P2Y12 receptor inhibitors should be considered as alternative medications.

Knowledge, perception, and confidence of hospital pharmacists toward pharmacogenetics in Jeddah, Kingdom of Saudi Arabia

Background

Integrating pharmacogenetics (PGx) testing into clinical practice leads to personalized medicine, which improves treatments’ efficacy and safety. Successful implementation of such a service requires sufficient knowledge, perception, and self-confidence among healthcare providers, especially pharmacists.

Objectives

To evaluate governmental hospital pharmacists’ knowledge, perception, and self-confidence toward PGx testing in Jeddah, Kingdom of Saudi Arabia.

Method

This cross-sectional study was conducted using previously validated questionnaire. Pharmacists working in five randomly selected general governmental hospitals in Jeddah between August and October 2019 were interviewed. Comparative and descriptive analyses were used to analyze the data, and the significance level was at P-value < 0.05.

Results

A total of 119 pharmacists with a mean (±SD) age of 31.2 (±5.05) years were included with a response rate of 79.3%. The average total mean (±SD) score for PGx knowledge-based questions was low (2.4 ± 1.09 out of 5). Most of the participants, with a total mean score of (10.1 ± 1.6 out of 12), revealed a positive perception toward PGx testing and its implications. A moderate self-confidence score for utilizing PGx testing (4.3 ± 2.3 out of 8) was observed among the participants. Pharmacists who had completed postgraduate studies had a statistically higher mean knowledge score (P = 0.006) compared with pharmacists with undergraduate degrees.

Conclusion

Governmental hospital pharmacists have limited knowledge and understanding about PGx testing; however, the majority expressed a high level of awareness and agreed that PGx testing is a valuable tool for enhancing drug efficacy and safety. The study also highlighted the importance of improving pharmacists’ knowledge about PGx testing, which will help them in implementing such a valuable service into their clinical practice in Saudi hospitals.

Development and Validation of a Novel Warfarin Dosing Algorithm for Korean Patients With VKORC1 1173C

BACKGROUND

Differences in the performance of suggested warfarin dosing algorithms among different ethnicities and genotypes have been reported; this necessitates the development of an algorithm with enhanced performance for specific population groups. Previous warfarin dosing algorithms underestimated warfarin doses in VKORC1 1173C carriers. We aimed to develop and validate a new warfarin dosing algorithm for Korean patients with VKORC1 1173C.

METHODS

A total of 109 patients carrying VKORC1 1173CT (N=105) or 1173CC (N=4) were included in this study. Multiple regression analysis was performed to deduce a new dosing algorithm. Following literature searches for genotype-guided warfarin dosing algorithms, 21 algorithms were selected and evaluated using the correlation coefficient (ρ) of actual dose and estimated dose, mean error, and root mean square error.

RESULTS

The developed algorithm is as follows: maintenance dose (mg/week)=exp [3.223-0.009×(age)+0.577×(body surface area [BSA])+0.178×(sex)-0.481×(CYP2C9 genotype)+0.227×(VKORC1 genotype)]. Integrated variables explained 44% of the variance in the maintenance dose. The predicted and actual doses showed moderate correlation (ρ=0.641) with the best performance with a mean error of -1.30 mg/week. The proportion of underestimated groups was 17%, which was lower than with the other algorithms.

CONCLUSIONS

This is the first study to develop and validate a warfarin dosing algorithm based on data from VKORC1 1173C carriers; it showed superior predictive performance compared with previously published algorithms.

Survey of physicians' views on the clinical implementation of pharmacogenomics-based personalized therapy

Despite quantitative increases and qualitative advances in pharmacogenomics (PGx) research, the clinical implementation of PGx-based personalized therapy has still been limited. The objective of this study was to assess physicians' self-reported knowledge of PGx-based personalized therapy, and to explore the most problematic and highest priority barriers preventing physicians from applying PGx into clinical practice under the Korean healthcare system. A 36-question survey was distributed to 53 physicians with various specialties in Korea. In the physicians' self-perceived knowledge, twenty-eight physicians (53%) reported a lack sufficient knowledge about PGx. The perceived largest barrier to clinical implementation of PGx was the high cost of PGx testing, followed by a lack of PGx education for healthcare providers or lack of clinical PGx experts. Physicians without clinical PGx experience or with indirect experience reported that the largest barrier to clinical implementation of PGx was the high cost of PGx testing, while physicians with clinical PGx experience pointed out that a lack of patients' education was the major concern, followed by a lack of PGx education for healthcare providers or lack of clinical PGx experts. The highest priority problem was reported to be a lack of actionable guidelines for drug selection and dosing using PGx. In conclusion, we should increase and expand extensive educational programs for healthcare providers and patients, and to develop and establish a clinical decision support systems for PGx-based personalized therapy in Korea.

Drug Use in Denmark for Drugs Having Pharmacogenomics (PGx) Based Dosing Guidelines from CPIC or DPWG for CYP2D6 and CYP2C19 Drug-Gene Pairs: Perspectives for Introducing PGx Test to Polypharmacy Patients

Background: The cytochrome P450 drug metabolizing enzymes CYP2D6 and CYP2C19 are the major targets for pharmacogenomics (PGx) testing and determining for drug response. Clinical dosing guidelines for specific drug-gene interactions (DGI) are publicly available through PharmGKB. The aim of this register study was to map the use of drugs in Denmark for drugs having actionable dosing guidelines (AG) i.e., dosing recommendations different from standard dosing for CYP2D6 or CYP2C19 DGI in terms of consumption. Methods: The Danish Register of Medicinal Product Statistics was the source to retrieve consumption in Defined Daily Dose (DDD) i.e., the assumed average maintenance dose per day for a drug used for its main indication in adults and number of users (2017 data). Clinical dosing guidelines were available from the PharmGKB website. Results: Forty-nine drugs have guidelines corresponding to 14.5% of total sales in DDD. Twenty-eight drugs have AG corresponding to 375.2 million DDD. Pantoprazole, lansoprazole, omeprazole, clopidogrel, and metoprolol constituted fifty-eight percent of the consumption in DDD of drugs having AG. The consumption of antidepressant drugs, opioids, and antipsychotic drugs were 157.0 million DDD; with 441,850 users, 48.9 million DDD; with 427,765 users, and 23.7 million DDD; with 128,935 users, respectively. Age distributions of consumption of drugs and drug combinations, e.g., for sertraline redeemed either alone or in combination with metoprolol and tramadol, are presented. Conclusion: This exploratory register study clearly showed that a large fraction of the Danish population, especially the elderly, are exposed to drugs or drug combinations for which there exist AG related to PGx of CYP2D6 or CYP2C19.

Predicting (side) effects for patients with inflammatory bowel disease: The promise of pharmacogenetics

Inflammatory bowel disease (IBD) is a chronic and heterogeneous intestinal inflammatory disorder. The medical management of IBD aims for long-lasting disease remission to prevent complications and disease progression. Early introduction of immunosuppression forms the mainstay of medical IBD management. Large inter-individual variability in drug responses, in terms of both efficacy and toxicity, leads to high rates of therapeutic failure in the management of IBD. Better patient stratification is needed to maximize patient benefit and minimize the harm caused by adverse events. Pre-treatment pharmacogenetic testing has the potential to optimize drug selection and dose, and to minimize harm caused by adverse drug reactions. In addition, optimizing the use of cheap conventional drugs, and avoiding expensive ineffective drugs, will lead to a significant reduction in costs. Genetic variation in both TPMT and NUDT15, genes involved in thiopurine metabolism, is associated to an increased risk of thiopurine-induced myelosuppression. Moreover, specific HLA haplotypes confer risk to thiopurine-induced pancreatitis and to immunogenicity to tumor necrosis factor-antagonists, respectively. Falling costs and increased availability of genetic tests allow for the incorporation of pre-treatment genetic tests into clinical IBD management guidelines. In this paper, we review clinically useful pharmacogenetic associations for individualized treatment of patients with IBD and discuss the path from identification of a predictive pharmacogenetic marker to implementation into IBD clinical care.

Pathway genes and metabolites in thiopurine therapy in Korean children with acute lymphoblastic leukaemia

AIMS

We aimed to investigate the impact of various genetic polymorphisms affecting thiopurine metabolism pathways and toxicity in paediatric acute lymphoblastic leukaemia patients for the first time in Korea.

METHODS

From May 2006 to September 2016, 139 paediatric acute lymphoblastic leukaemia patients treated with combination chemotherapy including 6-mercaptopurine were included in the study. One hundred and twenty-three variants in 43 genes, including TMPT and NUDT15, were screened using targeted genotyping, such as a MassARRAY system, direct sequencing and polymerase chain reaction-restriction fragment length polymorphism methods. Among the polymorphisms screened, 103 polymorphisms of 43 genes were included for further analyses.

RESULTS

The genetic polymorphisms in the ABCC4, AHCY, ATIC, FAM8A6P, GART, GNG2, GSTA1, MTHFD1, MTHFR, NUDT15, PACSIN2, TYMS and XDH genes, and an intronic polymorphism between HIVEP2 and AIG1, and TPMT genotype were associated with thiopurine metabolism (P < 0.05). Genetic polymorphisms in the ABCC4, ADK, ATIC, GART, GMPS, GSTP1, IMPDH1, ITPA, KCNMA1, MOCOS, MTRR, NUDT15, SLC19A1, SLC28A3, SLC29A1, SLCO1B1, TYMP and XDH genes were associated with thiopurine-related toxicities; neutropenia, hepatotoxicity and treatment interruption (P < 0.05).

CONCLUSIONS

Findings of this study may provide basic knowledge for personalized medicine for thiopurinxe treatment in paediatric acute lymphoblastic leukaemia patients.

The pharmacogenetics of medications used in general anesthesia

General anesthesia is a state of unconsciousness, amnesia, analgesia and akinesia induced by drugs including opioids, hypnotic-sedative agents, muscle relaxants and antiemetics. Clinical and genetic factors are reported to influence the efficacy and side effects of these agents. Based on the evidence, clinical action is needed to improve clinical outcomes. This review summarizes the latest knowledge with regards to the pharmacogenetics of anesthetics and general anesthesia related complications.

Association and clinical utility of NAT2 in the prediction of isoniazid-induced liver injury in Singaporean patients

BACKGROUND AND AIMS

Isoniazid (INH) is part of the first-line-therapy for tuberculosis (TB) but can cause drug-induced liver injury (DILI). Several candidate single nucleotide polymorphisms (SNPs) have been previously identified but the clinical utility of these SNPs in the prediction of INH-DILI remains uncertain. The aim of this study was to assess the association between selected candidate SNPs and the risk of INH-DILI and to assess the clinical validity of associated variants in a Singaporean population.

METHODS

This was a case-control study where 24 INH-DILI cases and 79 controls were recruited from the TB control unit in a tertiary hospital. Logistic regression was used to test for the association between candidate SNPs and INH-DILI. NAT2 acetylator status was inferred from genotypes and tested for association with INH-DILI. Finally, clinical validity measures were estimated for significant variants.

RESULTS

Two SNPs in NAT2 (rs1041983 and rs1495741) and NAT2 slow acetylators (SA) were significantly associated with INH-DILI (OR (95% CI) = 13.86 (4.30-44.70), 0.10 (0.03-0.33) and 9.98 (3.32-33.80), respectively). Based on an INH-DILI prevalence of 10%, the sensitivity, specificity, positive and negative predictive values of NAT2 SA were 75%, 78%, 28% and 97%, respectively. The population attributable fraction (PAF) and number needed to test (NNT) for NAT2 SA were estimated to be 0.67 and 4.08, respectively. A model with clinical and NAT2 acetylator status provided significantly better prediction for INH-DILI than a clinical model alone (area under receiver operating characteristic curve = 0.863 vs. 0.766, respectively, p = 0.027).

CONCLUSIONS

We show the association between NAT2 SA and INH-DILI in a Singaporean population and demonstrated its clinical utility in the prediction of INH-DILI.