A multiplex pharmacogenetics assay using the MinION nanopore sequencing device.

OBJECTIVES: The MinION nanopore sequencing device opens the opportunity to cost-effective and point-of-care DNA sequencing. As a proof of principle, we developed a multiplex assay targeting pharmacogenetic variants related to clopidogrel and warfarin, the two commonly used drugs that show response variability due to genetic polymorphisms. METHODS: Six reference and 78 clinical DNA samples were amplified by PCR to generate 15 amplicons targeting 27 key variants. These products were then barcoded to enable sample multiplexing in one sequencing run. Four variant calling tools (marginCaller, VarScan 2, nanopolish, Clairvoyante) were used to compare genotyping accuracy. RESULTS: In our cohort, 81 out of 84 samples were successfully sequenced and genotyped. Using nanopolish as the variant calling tool achieved accuracy >95% for all except two variants. A known single base deletion (CYP2C9*6) was successfully detected. CONCLUSION: While minor misgenotyping issues exist, this work demonstrates that drug-specific or broad pharmacogenetic screening assays using small PCR amplicons are possible on the MinION sequencing device.

Pharmacogenetics of angiotensin-converting enzyme inhibitor-induced angioedema.

Angioedema is a rare adverse effect of the commonly used angiotensin-converting enzyme inhibitors (ACEi) and is reported to occur with a prevalence of 0.1%-0.7%. Although most ACEi-induced angioedema (ACEi-A) cases are mild, severe cases requiring intensive care and even resulting in death have been reported in the literature. The mechanisms underlying ACEi-A are not yet fully understood, but bradykinin and/or substance P accumulation resulting from inhibition of ACE is believed to play a crucial role. ACEi-A occurs at variable frequencies across different racial groups, suggesting a genetic association with the development of ACEi-A. To date, one genome-wide association study and several candidate gene studies have been published on the association of genetic variation with ACEi-A. Genetic associations reported have been attributed to several distinct mechanisms: (a) genes coding for alternative enzymes responsible for the degradation of bradykinin and/or substance P in the diminution of ACE activity (b) ACE gene function, (c) bradykinin receptor genes, (d) genes implicated in immune and inflammation regulation and (e) genes in the fibrinolytic and coagulation pathway. Despite several plausible genetic associations, there are currently no genetic variants with sufficient effect to be clinically useful. The low incidence of ACEi-A suggests that a combination of genomic approaches with the capability to detect potentially important variants might be required to shed light on the mechanism of this adverse reaction. Additionally, many non-genetic risk factors associated with ACEi-A suggest the potential contribution of epigenetic dysregulation.

Allelic diversity of the pharmacogene CYP2D6 in New Zealand Maori and Pacific peoples.

The enzyme cytochrome P450 2D6 (CYP2D6) metabolises approximately 25% of commonly prescribed drugs, including analgesics, anti-hypertensives, and anti-depressants, among many others. Genetic variation in drug metabolising genes can alter how an individual responds to prescribed drugs, including predisposing to adverse drug reactions. The majority of research on the CYP2D6 gene has been carried out in European and East Asian populations, with many Indigenous and minority populations, such as those from Oceania, greatly underrepresented. However, genetic variation is often population specific and analysis of diverse ethnic groups can reveal differences in alleles that may be of clinical significance. For this reason, we set out to examine the range and frequency of CYP2D6 variants in a sample of 202 Maori and Pacific people living in Aotearoa (New Zealand). We carried out long PCR to isolate the CYP2D6 region before performing nanopore sequencing to identify all variants and alleles in these samples. We identified twelve variants which have previously not been reported in the PharmVar CYP2D6 database, three of which were exonic missense variations. Six of these occurred in single samples and one was found in 19 samples (9.4% of the cohort). The remaining five variants were identified in two samples each. Identified variants formed twelve new CYP2D6 suballeles and four new star alleles, now recorded in the PharmVar database. One striking finding was that CYP2D6*71, an allele of uncertain functional status which has been rarely observed in previous studies, occurs at a relatively high frequency (8.9%) within this cohort. These data will help to ensure that CYP2D6 genetic analysis for pharmacogenetic purposes can be carried out accurately and effectively in this population group.

Genome-wide impact of hydrogen peroxide on maintenance DNA methylation in replicating cells.

BACKGROUND: Environmental factors, such as oxidative stress, have the potential to modify the epigenetic landscape of cells. We have previously shown that DNA methyltransferase (DNMT) activity can be inhibited by sublethal doses of hydrogen peroxide (H2O2). However, site-specific changes in DNA methylation and the reversibility of any changes have not been explored. Using bead chip array technology, differential methylation was assessed in Jurkat T-lymphoma cells following exposure to H2O2. RESULTS: Sublethal H2O2 exposure was associated with an initial genome-wide decrease in DNA methylation in replicating cells, which was largely corrected 72 h later. However, some alterations were conserved through subsequent cycles of cell division. Significant changes to the variability of DNA methylation were also observed both globally and at the site-specific level. CONCLUSIONS: This research indicates that increased exposure to H2O2 can result in long-term alterations to DNA methylation patterns, providing a mechanism for environmental factors to have prolonged impact on gene expression.

Nanopore sequencing of the pharmacogene CYP2D6 allows simultaneous haplotyping and detection of duplications.

Aim: Long read sequencing offers the promise of overcoming some of the challenges in accurate genotyping of complex genes, along with the advantage of straightforward variant phasing. We have established methods for sequencing and haplotyping of the whole CYP2D6 gene using nanopore sequencing. Materials and methods: 32 samples covering various haplotypes including gene duplication were sequenced on the GridION platform. Results: Haplotypes of 52 alleles matched accurately to known star (*) allele subvariants, with the remaining 12 being assigned as new alleles, or new subvariants of known alleles. Duplicated alleles could be detected by analyzing the allelic balance. Conclusion: Nanopore sequencing of CYP2D6 offers a high throughput method for accurate haplotyping, detection of new variants and determination of duplicated alleles.

Contrasting signals of cardiovascular health among natriuretic peptides in subjects without heart disease.

Natriuretic Peptides (NP) are important in maintaining normal cardiac and metabolic status and have been used to predict cardiovascular events. Whether plasma concentrations of NP products within the normal range reflect cardio-metabolic health is unknown. Plasma NTproANP, NTproBNP and NTproCNP and their bioactive counterparts were measured in a random sample of 348 community dwellers aged 49-51 yr without heart disease and associations sought with established vascular risk factors, echocardiographic indices and a genetic variant previously linked with BNP. Stratified by sex, each of ten vascular risk factors were positively associated with NTproCNP whereas associations with NTproBNP and NTproANP were all negative. In both sexes, higher plasma NTproCNP was associated with higher arterial elastance, lower LV stroke volume and lower LV end diastolic volume. Exactly opposite associations were found with plasma NTproBNP or NTproANP. Sex specific differences were identified: positive association of NTproBNP with LV end systolic volume and the negative association with LV elastance were found only in males. The genetic variant rs198358 was independently associated with NTproBNP but not with NTproANP. In conclusion, higher NTproCNP is likely to be an adaptive response to impaired LV relaxation whereas genetic factors likely contribute to higher NTproBNP and improved cardio-metabolic health at midlife.