Age and CYP3A5 genotype affect tacrolimus dosing requirements after transplant in pediatric heart recipients. J Heart Lung Transplant. 2011;30:1352-1359. [PMID: 21930396 DOI: 10.1016/j.healun.2011.08.001]

Human Ontogeny of Drug Transporters: Review and Recommendations of the Pediatric Transporter Working Group

The critical importance of membrane-bound transporters in pharmacotherapy is widely recognized, but little is known about drug transporter activity in children. In this white paper, the Pediatric Transporter Working Group presents a systematic review of the ontogeny of clinically relevant membrane transporters (e.g., SLC, ABC superfamilies) in intestine, liver, and kidney. Different developmental patterns for individual transporters emerge, but much remains unknown. Recommendations to increase our understanding of membrane transporters in pediatric pharmacotherapy are presented.

CYP3A5*3 and POR*28 genetic variants influence the required dose of tacrolimus in heart transplant recipients

BACKGROUND

After heart transplantation (HTx), the interindividual pharmacokinetic variability of immunosuppressive drugs represents a major therapeutic challenge due to the narrow therapeutic window between over-immunosuppression causing toxicity and under-immunosuppression leading to graft rejection. Although genetic polymorphisms have been shown to influence pharmacokinetics of immunosuppressants, data in the context of HTx are scarce. We thus assessed the role of genetic variation in CYP3A4, CYP3A5, POR, NR1I2, and ABCB1 acting jointly in immunosuppressive drug pathways in tacrolimus (TAC) and ciclosporin (CSA) dose requirement in HTx recipients.

METHODS

Associations between 7 functional genetic variants and blood dose-adjusted trough (C0) concentrations of TAC and CSA at 1, 3, 6, and 12 months after HTx were evaluated in cohorts of 52 and 45 patients, respectively.

RESULTS

Compared with CYP3A5 nonexpressors (*3/*3 genotype), CYP3A5 expressors (*1/*3 or *1/*1 genotype) required around 2.2- to 2.6-fold higher daily TAC doses to reach the targeted C0 concentration at all studied time points (P ≤ 0.003). Additionally, the POR*28 variant carriers showed higher dose-adjusted TAC-C0 concentrations at all time points resulting in significant differences at 3 (P = 0.025) and 6 months (P = 0.047) after HTx. No significant associations were observed between the genetic variants and the CSA dose requirement.

CONCLUSIONS

The CYP3A5*3 variant has a major influence on the required TAC dose in HTx recipients, whereas the POR*28 may additionally contribute to the observed variability. These results support the importance of genetic markers in TAC dose optimization after HTx.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines for CYP3A5 Genotype and Tacrolimus Dosing

Tacrolimus is the mainstay immunosuppressant drug used after solid organ and hematopoietic stem cell transplantation. Individuals who express CYP3A5 (extensive and intermediate metabolizers) generally have decreased dose-adjusted trough concentrations of tacrolimus as compared with those who are CYP3A5 nonexpressers (poor metabolizers), possibly delaying achievement of target blood concentrations. We summarize evidence from the published literature supporting this association and provide dosing recommendations for tacrolimus based on CYP3A5 genotype when known (updates at www.pharmgkb.org).

Influence of donor-recipient CYP3A4/5 genotypes, age and fluconazole on tacrolimus pharmacokinetics in pediatric liver transplantation: a population approach

AIM

To characterize the effect of donor and recipient CYP3A4, CYP3A5 and ABCB1 genotypes as well as relevant patient characteristics on tacrolimus pharmacokinetics in pediatric liver transplantation.

PATIENTS & METHODS

Data from 114 pediatric liver transplant recipients were retrospectively collected during the first 3 months following transplantation. Population pharmacokinetic analysis was performed using nonlinear mixed effects modeling, including characterization of influential covariates.

RESULTS

A two-compartment model with first order elimination best fitted the data. Estimates of apparent volume of the central compartment, intestinal clearance, hepatic clearance and intercompartmental clearance were 79 l, 0.01 l/h, 10.9 l/h and 105 l/h, respectively. Time post-transplantation, recipient age, donor CYP3A5 and CYP3A4 genotypes and fluconazole administration significantly influenced tacrolimus apparent clearance while bodyweight influenced volume of distribution.

CONCLUSION

The proposed model displayed acceptable fitting performances and enabled identification of statistically significant and clinically relevant covariates on tacrolimus pharmacokinetics in the early pediatric post liver transplantation period.

Choosing the right dose of tacrolimus

Choosing the right dose of tacrolimus 'adapted to each individual patient' is a central question after transplantation. The pharmacokinetic behaviour of tacrolimus in paediatric patients is significantly influenced by clinical factors growth and maturation, as well as genetic factors. Large interindividual variability and narrow therapeutic index make dosage individualisation mandatory in children. CYP3A5 expressers require a 1.8-fold higher tacrolimus dose than non-expressers. A visual patient-tailored dosing chart, taking into consideration the child's weight, recent haematocrit level and CYP3A5 genotype, was developed based on a population pharmacokinetic-pharmacogenetic model, and can be used routinely to individualise tacrolimus starting dose. Area under the concentration-time curve-based dosage adaptation through limited sampling strategy and Bayesian estimation is more reliable than trough concentration. Therapeutic drug monitoring and dosage adaptation can be included in routine post-transplantation consultation and should be considered in the urgent situations (eg, rejection, adverse event, lack of compliance, change of coadministration drug with potential drug-drug interaction and other situations).

Association of CYP3A variants with kidney transplant outcomes

Cyclosporine is used extensively in kidney transplantation and is a substrate for cytochrome P450 enzymes. The role of cytochrome p450 polymorphisms in kidney transplant outcome has not yet been fully elucidated. We investigate the clinical impact of single nucleotide polymorphisms in CYP3A4, CYP3A5, PPARα, and POR*28 in 255 kidney transplant recipients. We examine for any association with graft survival, time to first cancer, and delayed graft function, and also measure cyclosporine levels at days 3, 10, and months 1, 3, 6, and 12 after transplantation. The CYP3A4*22 allele is significant associated with the development of cancer post-kidney transplantation (HR 0.20, 95% CI 0.07-0.57, p = 0.003). It is not significantly associated with graft survival. No other SNP's were associated with graft survival time to first cancer, or delayed graft function. There was a non-significant trend of lower cyclosporine dose requirement in CYP3A4*22 carriers. Independent replication of our findings is now warranted to confirm or reject the role of CYP3A variants in cancer development following kidney transplantation.

Drug metabolism for the paediatrician

Drug metabolism importantly determines drug concentrations. The efficacy and safety of many drugs prescribed for children are, therefore, dependent on intraindividual and interindividual variation in drug-metabolising enzyme activity. During growth and development, changes in drug-metabolising enzyme activity result in age-related differences in drug disposition, most pronounced in preterm infants and young infants. The shape of the developmental trajectory is unique to the drug-metabolising enzyme involved in the metabolism of individual drugs. Other factors impacting drug metabolism are underlying disease, drug-drug interactions and genetic variation. The interplay of age with these other factors may result in unexpected variation in drug metabolism in children of different ages. Extrapolation of adult data to guide drug dosing in children should be done with caution. The younger the child, the less reliable is the extrapolation. This review aims to identify the primary sources of variability of drug metabolism in children, the knowledge of which can ultimately guide the practitioner towards effective and safe drug therapy.

The tacrolimus metabolism rate influences renal function after kidney transplantation

The effective calcineurin inhibitor (CNI) tacrolimus (Tac) is an integral part of the standard immunosuppressive regimen after renal transplantation (RTx). However, as a potent CNI it has nephrotoxic potential leading to impaired renal function in some cases. Therefore, it is of high clinical impact to identify factors which can predict who is endangered to develop CNI toxicity. We hypothesized that the Tac metabolism rate expressed as the blood concentration normalized by the dose (C/D ratio) is such a simple predictor. Therefore, we analyzed the impact of the C/D ratio on kidney function after RTx. Renal function was analyzed 1, 2, 3, 6, 12 and 24 months after RTx in 248 patients with an immunosuppressive regimen including basiliximab, tacrolimus, mycophenolate mofetil and prednisolone. According to keep the approach simple, patients were split into three C/D groups: fast, intermediate and slow metabolizers. Notably, compared with slow metabolizers fast metabolizers of Tac showed significantly lower estimated glomerular filtration rate (eGFR) values at all the time points analyzed. Moreover, fast metabolizers underwent more indication renal biopsies (p = 0.006) which revealed a higher incidence of CNI nephrotoxicity (p = 0.015) and BK nephropathy (p = 0.024) in this group. We herein identified the C/D ratio as an easy calculable risk factor for the development of CNI nephrotoxicity and BK nephropathy after RTx. We propose that the simple C/D ratio should be taken into account early in patient's risk management strategies.

Personalized tacrolimus dose requirement by CYP3A5 but not ABCB1 or ACE genotyping in both recipient and donor after pediatric liver transplantation

Tacrolimus (TAC) is the backbone of an immunosuppressive drug used in most solid organ transplant recipients. A single nucleotide polymorphism (SNP) at position 6986G>A in CYP3A5 has been notably involved in the pharmacokinetic variability of TAC. It is hypothesized that CYP3A5 genotyping in patients may provide a guideline for TAC therapeutic regimen. To further evaluate the impact of CYP3A5 variants in donors and recipients, ABCB1 and ACE SNPs in recipients on TAC disposition, clinical and laboratory data were retrospectively reviewed from 90 pediatric patients with liver transplantation and their corresponding donors after 1 year of transplantation. The recipients with CYP3A5 *1/*1 or *1/*3 required more time to achieve TAC therapeutic range during the induction phase, and needed more upward dose during the late induction and the maintained phases, with lower C/D ratio, compared with those with CYP3A5 *3/*3. And donor CYP3A5 genotypes were found to impact on TAC trough concentrations after liver transplantation. No association between ABCB1 or ACE genotypes and TAC disposition post-transplantation was found. These results strongly suggest that CYP3A5 genotyping both in recipient and donor, not ABCB1 or ACE is necessary for establishing a personalized TAC dosage regimen in pediatric liver transplant patients.

Effect of CYP3A5 genotype, steroids, and azoles on tacrolimus in a pediatric renal transplant population

BACKGROUND

Numerous studies have described the impact of cytochrome P450 3A5 (CYP3A5) genotype on Tacrolimus (TAC) exposure. The purpose of this study was to conduct a comprehensive analysis of genetic and non-genetic factors affecting the TAC dose-exposure relationship over the first year post pediatric renal transplant.

METHODS

Data were collected retrospectively for the first year post-transplant in pediatric renal transplant patients receiving TAC maintenance immunosuppression. The effect of CYP3A5 genotype (CYP3A5*3 and *6 alleles), age, azoles, and corticosteroids on TAC trough concentration normalized for dose (TAC Co/D ng/ml/mg/kg/day) was assessed using a linear mixed model.

RESULTS

Over time, TAC Co/D was lower in recipients with CYP3A5*1/*3 genotype compared to those with CYP3A5*3/*3 genotype (44.5 ± 14.4 vs. 107.6 ± 6.4, p = 0.03), increased in patients >12 years of age compared to < 12 years (93.9 ± 8.7 vs. 53.1 ± 12.9, p = 0.007), and decreased by concomitant corticosteroids (69.5 ± 12.7 vs. 89.9 ± 20.0, p = 0.04). The observed increased TAC Co/D in the presence of azoles (271 ± 41 vs. 111 ± 91, p = 0.016) could be attributed to clotrimazole.

CONCLUSIONS

Multiple factors, including CYP3A5 genotype, and age, influence TAC Co/D in pediatric kidney transplant recipients. Clotrimazole administered as troches also contribute to TAC Co/D variability.

Pediatric perspective on pharmacogenomics

The advances in high-throughput genomic technologies have improved the understanding of disease pathophysiology and have allowed a better characterization of drug response and toxicity based on individual genetic make up. Pharmacogenomics is being recognized as a valid approach used to identify patients who are more likely to respond to medication, or those in whom there is a high probability of developing severe adverse drug reactions. An increasing number of pharmacogenomic studies are being published, most include only adults. A few studies have shown the impact of pharmacogenomics in pediatrics, highlighting a key difference between children and adults, which is the contribution of developmental changes to therapeutic responses across different age groups. This review focuses on pharmacogenomic research in pediatrics, providing examples from common pediatric conditions and emphasizing their developmental context.

CYP3A5 genotypes affect tacrolimus pharmacokinetics and infectious complications in Chinese pediatric liver transplant patients

Little information is available regarding the impact of cytochrome P450 (CYP) 3A5 on the metabolism of TAC in infant LTx. Therefore, the CYP3A5 genotype of Chinese pediatric recipients (intestine) as well as donors (graft liver) was performed for the purpose of establishing an optimal dosage regimen in children. Sixty-four patients were divided according to CYP3A5 genotype (expression of *1 allele: EX and NEX) for each recipient (R) and donor (D), EX-R/EX-D (n = 21), EX-R/NEX-D (n = 8), NEX-R/EX-D (n = 8) and NEX-R/NEX-D (n = 27). Results indicated that initial TAC daily dose requirement was higher among EX-R/EX-D children compared with those who did not express CYP3A5 (0.28 ± 0.10 vs. 0.19 ± 0.08 mg/kg/day, p < 0.01). CYP3A5 expression contributed an overall of 38.35% to its C/D ratios, and graft liver was a key determinant. Additionally, the EX-R/EX-D group showed significantly higher incidence of infectious complications, lower immune response and was an independent risk factor for the development of infections (odds ratio 3.86, p = 0.025). Donor CYP3A5 expression partially explains TAC dose requirement, the effect of CYP3A5 variation may influence clinical outcomes; therefore, monitoring immune response may be important for preventing risks associated with under- and over-immunosuppression.

CYP3A4*22 and CYP3A combined genotypes both correlate with tacrolimus disposition in pediatric heart transplant recipients

BACKGROUND

Tacrolimus metabolism depends on CYP3A4 and CYP3A5. We aimed to determine the relationship between the CYP3A4*22 polymorphism and combined CYP3A genotypes with tacrolimus disposition in pediatric heart transplant recipients.

METHODS

Sixty pediatric heart transplant recipients were included. Tacrolimus doses and trough concentrations were collected in the first 14 days post-transplantation. CYP3A phenotypes were defined as extensive (CYP3A5*1 + CYP3A4*1/*1 carriers), intermediate (CYP3A5*3/*3 + CYP3A4*1/*1 carriers) or poor (CYP3A5*3/*3 + CYP3A4*22 carriers) metabolizers.

RESULTS

CYP3A4*22 carriers needed 30% less tacrolimus (p = 0.016) to reach similar target concentrations compared with CYP3A4*1/*1 (n = 56) carriers. Poor CYP3A metabolizers required 17% (p = 0.023) less tacrolimus than intermediate and 48% less (p < 0.0001) than extensive metabolizers. Poor metabolizers showed 18% higher dose-adjusted concentrations than intermediate (p = 0.35) and 193% higher than extensive metabolizers (p < 0.0001).

CONCLUSION

Analysis of CYP3A4*22, either alone or in combination with CYP3A5*3, may help towards individualization of tacrolimus therapy in pediatric heart transplant patients.

Tacrolimus dose requirement in pediatric liver transplantation: influence of CYP3A5 gene polymorphism

AIM

Little information is available regarding the influence of CYP3A5 genetic polymorphisms on tacrolimus dose requirement in pediatric liver transplantation.

PATIENTS & METHODS

We performed a retrospective study among 179 pediatric liver recipients grafted between 2002 and 2009 in order to determine the influence of donor CYP3A5 genotype along with clinical variables on tacrolimus daily dose requirement during the first weeks following transplantation.

RESULTS

Mean stable tacrolimus daily dose requirement was higher among children who received a liver expressing CYP3A5 (carrying the CYPA3A5*1 allele) compared with those with a liver that did not express CYP3A5 (CYP3A5*3/*3 genotype): 0.29 ± 0.20 vs 0.18 ± 0.13 mg.kg(-1).d(-1), p = 0.005, respectively. A younger recipient age and fluconazole prescription were also significantly associated with tacrolimus daily dose requirement. Time to reach stable tacrolimus therapeutic trough concentrations was prolonged among patients with a CYP3A5-expressing graft (26 vs 21 days, p = 0.04).

CONCLUSION

Donor CYP3A5 genotype partially explains tacrolimus dose requirement. Original submitted 30 January 2013; Revision submitted 2 May 2013.

Stem cells in pediatric cardiology

The ability to reprogram virtually any cell of human origin to behave like embryonic or pluripotent stem cells is a major breakthrough in stem cell biology. Human induced pluripotent stem cells (iPSC) provide a unique opportunity to study "disease in a dish" within a defined genetic and environmental background. Patient-derived iPSCs have been successfully used to model cardiomyopathies, rhythm disorders and vascular disorders. They also provide an exciting opportunity for drug discovery and drug repurposing for disorders with a known molecular basis including childhood onset heart disease, particularly cardiac genetic disorders. The review will discuss their use in drug discovery, efficacy and toxicity studies with emphasis on challenges in pediatric-focused drug discovery. Issues that will need to be addressed in the coming years include development of maturation protocols for iPSC-derived cardiac lineages, use of iPSCs to study not just cardiac but extra-cardiac phenotypes in the same patient, scaling up of stem cell platforms for high-throughput drug screens, translating drug testing results to clinical applications in the paradigm of personalized medicine, and improving both the efficiency and the safety of iPSC-derived lineages for future stem cell therapies.

A published pharmacogenetic algorithm was poorly predictive of tacrolimus clearance in an independent cohort of renal transplant recipients

AIMS

An algorithm based on the CYP3A5 genotype to predict tacrolimus clearance to inform the optimal initial dose was derived using data from the DeKAF study (Passey et al. Br J Clin Pharmacol 2011; 72: 948-57) but was not tested in an independent cohort of patients. Our aim was to test whether the DeKAF dosing algorithm could predict estimated tacrolimus clearance in renal transplant recipients at our centre.

METHODS

Predicted tacrolimus clearance based on the DeKAF algorithm was compared with dose-normalized trough whole-blood concentrations (estimated clearance) on day 7 after transplantation in a single-centre cohort of 255 renal transplant recipients.

RESULTS

There was a weak correlation (r = 0.431) between clearance based on dose-normalized trough whole-blood concentrations and DeKAF algorithm-predicted clearance. The means of the tacrolimus clearance predicted by the DeKAF algorithm and the estimated tacrolimus clearance based on the dose-normalized trough blood concentrations were plotted against the differences in the clearance as a Bland-Altman plot. Logarithmic transformation was performed owing to the increased difference in tacrolimus clearance as the mean clearance increased. There was a highly significant systematic error (P < 0.0005) characterized by a sloped regression line [gradient, 0.88 (95% confidence interval, 0.75-1.01)] on the Bland-Altman plot.

CONCLUSIONS

The DeKAF algorithm was unable to predict the estimated tacrolimus clearance accurately based on real tacrolimus doses and blood concentrations in our cohort of patients. Other genes are known to influence the clearance of tacrolimus, and a polygenic algorithm may be more predictive than those based on a single genotype.

A Markov chain model to evaluate the effect of CYP3A5 and ABCB1 polymorphisms on adverse events associated with tacrolimus in pediatric renal transplantation

The SNP A6986G of the CYP3A5 gene (*3) results in a non-functional protein due to a splicing defect whereas the C3435T was associated with variable expression of the ABCB1 gene, due to protein instability. Part of the large interindividual variability in tacrolimus efficacy and toxicity can be accounted for by these genetic factors. Seventy-two individuals were examined for A6986G and C3435T polymorphism using a PCR-RFLP-based technique to estimate genotype and allele frequencies in the Jordanian population. The association of age, hematocrit, platelet count, CYP3A5, and ABCB1 polymorphisms with tacrolimus dose- and body-weight-normalized levels in the subset of 38 pediatric renal transplant patients was evaluated. A Markov model was used to evaluate the time-dependent probability of an adverse event occurrence by CYP3A5 phenotypes and ABCB1 genotypes. The time-dependent probability of adverse event was about double in CYP3A5 non-expressors compared to the expressors for the first 12 months of therapy. The CYP3A5 non-expressors had higher corresponding normalized tacrolimus levels compared to the expressors in the first 3 months. The correlation trend between probability of adverse events and normalized tacrolimus concentrations for the two CYP3A5 phenotypes persisted for the first 9 months of therapy. The differences among ABCB1 genotypes in terms of adverse events and normalized tacrolimus levels were only observed in the first 3 months of therapy. The information on CYP3A5 genotypes and tacrolimus dose requirement is important in designing effective programs toward management of tacrolimus side effects particularly for the initial dose when tacrolimus blood levels are not available for therapeutic drug monitoring.

Pharmacogenomics and heart failure in congenital heart disease

Congenital heart disease (CHD) constitutes a lifelong challenge in heart failure management. Current therapy is based mainly on physiologic principles extrapolated from the management of left ventricular failure in adult populations with either ischemic or nonischemic cardiomyopathy. However, there is good evidence of genomic variability in the origin and progression of CHD that suggests the need for a individualized approach to treatment. The developing science of pharmacogenomics presents an opportunity for CHD management broadly, and especially in the context of heart failure. There is growing evidence that individualizing drug therapy for these patients might be beneficial, and that prediction of response to therapy might be possible by incorporating genomic data into the treatment algorithm for individual patients.

Pediatric transplantation: opportunities for pharmacogenomics and genomics

Heterogeneity is the rule among pediatric heart transplant recipients. Patients vary in age, size, organ maturity, immune system maturity and underlying disease etiology, which can all influence post-transplant outcomes. Overall, the survival of pediatric transplant recipients continues to improve and the goal remains long-term survival of the primary graft and mitigation of long-term complications and adverse events. The evolving fields of pharmacogenomics and genomics have the potential to revolutionize and personalize the care of pediatric transplant recipients, and although clinical validation in a pediatric cohort is lacking, many of these technologies are becoming more readily available. We discuss genotype-guided dosing of immunosuppressant medications and other commonly used medications after transplantation, the influence of donor and recipient genotype on risk of post-transplant complications, genotype-guided selection of therapies to treat complications, and the use of next-generation sequencing for noninvasive detection of graft rejection.

Prevalence of renal dysfunction in tacrolimus-treated pediatric transplant recipients: a systematic review

Renal dysfunction after non-renal transplantation in adult tacrolimus-treated transplant patients is well documented. Little is known about its prevalence in children. Age-related changes in both disposition and effect of tacrolimus as well as renal function may preclude extrapolation of adult data to children. To systematically review the literature on renal dysfunction in non-renal pediatric transplant recipients treated with tacrolimus. PubMed/Medline, Embase, and Google were searched from their inception until April 19, 2012, with the search terms "tacrolimus," "renal function," "transplantation," and "children." Eighteen of 385 retrieved papers were considered relevant. Twelve dealt with liver, four with heart transplant, one with heart and lung transplant, and one with intestinal recipients. Reported prevalences of mild and severe chronic kidney disease ranged from 0% to 39% and 0% to 71.4%, respectively, for liver, and from 22.7% to 40% and 6.8% to 46%, respectively, for heart and/or lung transplant recipients. Ranges remained wide after adjusting for follow-up time and disease severity. Possible explanations are inclusion bias and definitions used for renal dysfunction. A considerable proportion of pediatric non-renal transplant patients who receive tacrolimus-based immunosuppression, appear to suffer from chronic kidney disease. This conclusion warrants further research into the real risk, its risk factors, and individualization of immunosuppressant therapy.

Stem cells in pediatric cardiology

The ability to reprogram virtually any cell of human origin to behave like embryonic or pluripotent stem cells is a major breakthrough in stem cell biology. Human induced pluripotent stem cells (iPSC) provide a unique opportunity to study "disease in a dish" within a defined genetic and environmental background. Patient-derived iPSCs have been successfully used to model cardiomyopathies, rhythm disorders and vascular disorders. They also provide an exciting opportunity for drug discovery and drug repurposing for disorders with a known molecular basis including childhood onset heart disease, particularly cardiac genetic disorders. The review will discuss their use in drug discovery, efficacy and toxicity studies with emphasis on challenges in pediatric-focused drug discovery. Issues that will need to be addressed in the coming years include development of maturation protocols for iPSC-derived cardiac lineages, use of iPSCs to study not just cardiac but extra-cardiac phenotypes in the same patient, scaling up of stem cell platforms for high-throughput drug screens, translating drug testing results to clinical applications in the paradigm of personalized medicine, and improving both the efficiency and the safety of iPSC-derived lineages for future stem cell therapies.

Personalized medicine in pediatric cardiology: do little changes make a big difference?

PURPOSE OF REVIEW

Advances in genomics have paved the way for personalized medicine applications. This review will discuss new discoveries in genomics and pharmacogenomics in children with congenital heart disease (CHD) and the application towards the development of new diagnostics, disease risk predictions, and optimizing response to drugs and surgery.

RECENT FINDINGS

Recent advances have identified common and rare variants associated with complex CHD using next-generation sequencing and genotyping technology. Next-generation sequencing is now being used not only for clinical genetic testing but also for noninvasive prenatal testing of fetal DNA in maternal serum to diagnose genetic conditions like fetal aneuploidies as early as the first trimester. This approach is not only more accurate but also safer than invasive maternal screening tests. This technology may also help in noninvasive diagnosis of transplant rejection. As genetic variations that influence the response to surgery in CHD are identified, this can guide decision-making surrounding optimum type and timing of surgery. Drug choice and dosing are being increasingly influenced by knowledge of pharmacogenetic and pharmacodynamic variations. Age-related and maturation-related changes in drug pharmacokinetics make it crucial to perform pediatric-targeted pharmacogenetic studies to enable the incorporation of age into genotype-guided drug dosing algorithms.

SUMMARY

Rapid genomic and pharmacogenomic discovery are guiding the development of more sensitive screening and diagnostic tests for CHD as well as development of safer and more effective drugs. This needs to be paralleled by the development of strategies to support rapid translation of emerging genomic knowledge to patient care.

Genetic and genomic approaches to the detection of heart transplant rejection

Since Christiaan Barnard performed the first heart transplant in 1967, over 100,000 heart transplants have been performed worldwide. As was true then, rejection remains the major threat to the function and survival of the allograft. The development of the endomyocardial biopsy as a means to monitor for rejection has allowed heart transplantation to thrive as a therapy for patients with end-stage heart disease. The need for a noninvasive method of rejection surveillance led to the development of the first genetic test for allograft rejection, the AlloMap^®. In this article, after presenting the pathological and clinical features of cardiac allograft rejection, the authors discuss the development and application of gene-expression testing for the detection of cardiac allograft rejection. We then explore emerging 'omic' approaches that will be the rejection detection methods of the future.

Personalized Medicine in the Genomics Era: highlights from an international symposium on childhood heart disease

As the population of childhood heart disease survivors grows, a better understanding of the genetic underpinnings of heart disease is needed to improve diagnostics, therapeutics and outcomes. The Trans-Atlantic Research Network, GenomeHeart and The SickKids Heart Centre Biobank hosted an international symposium on childhood heart disease titled 'Personalized Medicine in the Genomics Era'. Experts in cardiology, developmental biology, genomics, pharmacology, bioinformatics, stem cell biology, ethics and biobanking shared their knowledge and expertise. The 2-day symposium hosted participants from North America, Europe and Asia including scientists, physicians, nurses, trainees and representatives from industry partners, federal and provincial funding agencies, and patient and community groups. The symposium focused on international research partnerships and application of current state-of-the-art in genomics and stem cell medicine towards personalized healthcare for childhood onset heart disease.

The interactions of age, sex, body mass index, genetics, and steroid weight-based doses on tacrolimus dosing requirement after adult kidney transplantation

PURPOSE

The aim of this study was to evaluate the effect of different clinical covariates on tacrolimus dose requirements in adult kidney transplant patients with a specific focus on drug interactions.

PATIENTS

Tacrolimus dosing requirement, normalized by drug levels and expressed as the concentration/dose (C/D) ratio as a surrogate index of tacrolimus bioavailability, was employed to identify four categories of tacrolimus dosing requirement, namely, very high, high, small, and very-small, in very fast, fast, slow, and very slow metabolizers, respectively. Steroid weight-based doses were analyzed instead of fixed doses, and genetic analysis of cytochrome P450 (CYP) 3A5*1/*3 and multi-drug resistance 1 (MDR1) C3435T and C1236T polymorphisms were performed

RESULTS

Multivariate analysis on 450 adult transplant patients identified six risk factors for being slow metabolizers and therefore requiring small tacrolimus doses: male sex (OR 1.615, p = 0.020); age >60 years (OR 2.456, p = 0.0005); body mass index ≥ 25 (OR 1.546, p = 0.046), hepatitis C virus positivity (OR 2.800, p = 0.0004); low steroid dose <0.06 mg/kg (OR 3.101, p < 0.0001). Patients with a small tacrolimus requirement were at increased risk for multiple infections (OR 1.533, p = 0.0008) and higher systolic blood pressure (OR 1.385, p = 0.022) and showed a significant association with the CYP3A5*3/*3 genotype adjusted by MDR1 polymorphisms C3435T and C1236T (OR 8.104, p = 0.0001).

CONCLUSIONS

Our results demonstrate the importance of the interaction among genetic and clinical factors in conditioning tacrolimus disposition, with corticosteroid weight-based dose being the only modifiable risk factor for tacrolimus requirement. As the tacrolimus dosing requirement increases with increasing tacrolimus clearance through concomitant steroid use, undesirable changes in tacrolimus levels may occur when steroid doses are tapered, predominantly in slow metabolizers. This often neglected drug interaction has to be monitored to optimize tacrolimus exposure in kidney transplant patients.