The Pennsylvania State University College of Medicine 1990 Bernard B. Brodie Lecture. Pharmacogenetics: past and future

Feasibility of preemptive pharmacogenetic testing and improvement of medication treatment satisfaction among medically underserved patients

Previous findings suggest that medically underserved patients are prescribed medications with pharmacogenetic (PGx) guidelines at a high frequency. Thus, underserved patients may especially benefit from PGx testing, but little evidence exists regarding the effect of testing in this population. This pilot study aimed to generate key feasibility data and explore clinical outcomes of PGx implementation in underserved populations. Black and Latino patients were recruited from an outpatient clinic and underwent PGx testing. Feasibility measures included enrollment metrics and actionable genotype frequencies. The primary clinical outcome was patient medication treatment satisfaction 6 months after testing. Implementation outcomes included the number of healthcare provider encounters and medication changes within the 6-month follow-up. Effectiveness outcomes included medication adherence, patient-perceived test value, and time spent discussing medications with providers. Ninety-nine patients completed the study. Proton-pump inhibitors were the most frequent PGx drug class prescribed at baseline (61%) followed by nonsteroidal anti-inflammatory drugs (36%). Patients with an actionable genotype constituted 96% of the population, whereas 28% had an actionable genotype related to their PGx drug. Patient treatment satisfaction significantly increased over the 6 months after PGx testing. In addition, medication adherence and the number of provider encounters significantly increased over the study period. In a pilot study, preemptive PGx testing was feasible in primary care clinics, improved patient treatment satisfaction and adherence, and increased the number of provider encounters in medically underserved patients. Future clinical trials are warranted to assess the long-term effects of PGx testing in a larger diverse patient population.

Utility of pharmacogenetic testing to optimise antidepressant pharmacotherapy in youth: a narrative literature review

Pharmacogenetics (PGx) is the study and application of how interindividual differences in our genomes can influence drug responses. By evaluating individuals' genetic variability in genes related to drug metabolism, PGx testing has the capabilities to individualise primary care and build a safer drug prescription model than the current "one-size-fits-all" approach. In particular, the use of PGx testing in psychiatry has shown promising evidence in improving drug efficacy as well as reducing toxicity and adverse drug reactions. Despite randomised controlled trials demonstrating an evidence base for its use, there are still numerous barriers impeding its implementation. This review paper will discuss the management of mental health conditions with PGx-guided treatment with a strong focus on youth mental illness. PGx testing in clinical practice, the concerns for its implementation in youth psychiatry, and some of the barriers inhibiting its integration in clinical healthcare will also be discussed. Overall, this paper provides a comprehensive review of the current state of knowledge and application for PGx in psychiatry and summarises the capabilities of genetic information to personalising medicine for the treatment of mental ill-health in youth.

An Introductory Tutorial on Cardiovascular Pharmacogenetics for Healthcare Providers

Pharmacogenetics can improve clinical outcomes by reducing adverse drug effects and enhancing therapeutic efficacy for commonly used drugs that treat a wide range of cardiovascular diseases. One of the major barriers to the clinical implementation of cardiovascular pharmacogenetics is limited education on this field for current healthcare providers and students. The abundance of pharmacogenetic literature underscores its promise, but it can also be challenging to learn such a wealth of information. Moreover, current clinical recommendations for cardiovascular pharmacogenetics can be confusing because they are outdated, incomplete, or inconsistent. A myriad of misconceptions about the promise and feasibility of cardiovascular pharmacogenetics among healthcare providers also has halted clinical implementation. Therefore, the main goal of this tutorial is to provide introductory education on the use of cardiovascular pharmacogenetics in clinical practice. The target audience is any healthcare provider (or student) with patients that use or have indications for cardiovascular drugs. This tutorial is organized into the following 6 steps: (1) understand basic concepts in pharmacogenetics; (2) gain foundational knowledge of cardiovascular pharmacogenetics; (3) learn the different organizations that release cardiovascular pharmacogenetic guidelines and recommendations; (4) know the current cardiovascular drugs/drug classes to focus on clinically and the supporting evidence; (5) discuss an example patient case of cardiovascular pharmacogenetics; and (6) develop an appreciation for emerging areas in cardiovascular pharmacogenetics. Ultimately, improved education among healthcare providers on cardiovascular pharmacogenetics will lead to a greater understanding for its potential in improving outcomes for a leading cause of morbidity and mortality.

Flattening and Unpacking Human Genetic Variation in Mexico, Postwar to Present

Argument This paper analyzes the research strategies of three different cases in the study of human genetics in Mexico - the work of Rubén Lisker in the 1960s, INMEGEN's mapping of Mexican genomic diversity between 2004 and 2009, and the analysis of Native American variation by Andrés Moreno and his colleagues in contemporary research. We make a distinction between an approach that incorporates multiple disciplinary resources into sampling design and interpretation (unpacking), from one that privileges pragmatic considerations over more robust multidisciplinary analysis (flattening). These choices have consequences for social, demographic, and biomedical practices, and also for accounts of genetic variation in human populations. While the former strategy unpacks fine-grained genetic variation - favoring precision and realism, the latter tends to flatten individual differences and historical depth in lieu of generalization.

Pharmacogenetics: Its Place in Medicine and Biology

A young science serves its purpose if it leads not only to new knowledge, but to new insights and concepts. This article opens with examples to illustrate some former thinking that the introduction of pharmacogenetic has overcome. Pharmacogenetic case histories from discovery to the present illustrate the interlocking of observations, technical advances, and changing concepts. There are striking biological similarities between pharmacogenetics and those inborn factors that cause resistance to infectious disease: Both represent person-to-person variations that may help the survival of populations, one when facing massive toxic exposures, the other when facing plagues and epidemics. Thus pharmacogenetics represents a biologically necessary variability of the defenses against chemical intruders, and this includes drugs. While this variability is desirable, drug toxicity occurring on the basis of this variability must be avoided. The most successful defendants against toxicity due to polymorphic (ie, high incidence) variants should be the designers of new drugs. The only defender concerned with rare variants can be the attentive clinician.

Pharmacogenetics and human genetic polymorphisms

The term pharmacogenetics was first used in the late 1950s and can be defined as the study of genetic factors affecting drug response. Prior to formal use of this term, there was already clinical data available in relation to variable patient responses to the drugs isoniazid, primaquine and succinylcholine. The subject area developed rapidly, particularly with regard to genetic factors affecting drug disposition. There is now comprehensive understanding of the molecular basis for variable drug metabolism by the cytochromes P450 and also for variable glucuronidation, acetylation and methylation of certain drugs. Some of this knowledge has already been translated to the clinic. The molecular basis of variation in drug targets, such as receptors and enzymes, is generally less well understood, although there is consistent evidence that polymorphisms in the genes encoding the β-adrenergic receptors and the enzyme vitamin K epoxide reductase is of clinical importance. The genetic basis of rare idiosyncratic adverse drug reactions had also been examined. Susceptibility to reactions affecting skin and liver appears to be determined in part by the HLA (human leucocyte antigen) genotype, whereas reactions affecting the heart and muscle may be determined by polymorphisms in genes encoding ion channels and transporters respectively. Genome-wide association studies are increasingly being used to study drug response and susceptibility to adverse drug reactions, resulting in identification of some novel pharmacogenetic associations.

Pharmacogenomics: a systems approach

Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. Pharmacogenetics-pharmacogenomics represents a major component of the movement to 'individualized medicine'. Pharmacogenetic studies originally focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire 'pathways' that include both pharmacokinetics (PKs)--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics (PDs), factors associated with the drug target(s), as well as genome-wide approaches. The convergence of advances in pharmacogenetics with rapid developments in human genomics has resulted in the evolution of pharmacogenetics into pharmacogenomics. At the same time, studies of drug response are expanding beyond genomics to encompass pharmacotranscriptomics and pharmacometabolomics to become a systems-based discipline. This discipline is also increasingly moving across the 'translational interface' into the clinic and is being incorporated into the drug development process and governmental regulation of that process. The article will provide an overview of the development of pharmacogenetics-pharmacogenomics, the scientific advances that have contributed to the continuing evolution of this discipline, the incorporation of transcriptomic and metabolomic data into attempts to understand and predict variation in drug response phenotypes as well as challenges associated with the 'translation' of this important aspect of biomedical science into the clinic.

Pharmacogenetics and Pharmacogenomics: Development, Science, and Translation

Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. This discipline evolved from the convergence of rapid advances in molecular pharmacology and genomics. Originally, pharmacogenetic studies focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire "pathways" encoding proteins that influence both pharmacokinetics--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics, the drug target itself, as well as genome-wide approaches. Pharmacogenomics is also increasingly moving across the "translational interface" into the clinic and is being incorporated into the drug development process and the governmental regulation of that process. However, significant challenges remain to be overcome if pharmacogenetics-pharmacogenomics is to achieve its full potential as a major medical application of genomic science.

Pharmacogenetics, race, and psychiatry: prospects and challenges

Although the field of pharmacogenetics has existed for nearly 50 years, it has begun to enter mainstream clinical practice only recently. Researchers and clinicians have now demonstrated that a wide assortment of genetic variants influence how individuals respond to medications. Many of these variants are relevant for psychiatry, affecting how patients respond to most antidepressants, antipsychotics, anxiolytics, and mood stabilizers. Enthusiasts hope that pharmacogenetics will soon usher in a new era of individualized medicine. However, determining the practical relevance of pharmacogenetic variants remains difficult, in part because of problems with study design and replication, and in part because a host of nongenetic factors (including age, diet, environmental exposures, and comorbid diseases) also influence how individuals respond to medications. Since individualized pharmacogenetic assessment remains difficult, some researchers have argued that race provides a convenient proxy for individual genetic variation, and that clinicians should choose medications and doses differently for different races. This approach remains extremely controversial because of the complexity of the genetic structure of the human population, the complexity of gene-environment interactions, and the complexity of the meanings of race in the United States.

From pharmacokinetics to pharmacogenomics: a new approach to tailor immunosuppressive therapy

One of the main tasks in the management of organ transplantation is the optimization of immunosuppressive therapy, in order to provide therapeutic efficacy limiting drug-related toxicity. In the past years major efforts have been carried out to define therapeutic windows based on blood/plasma levels of each immunosuppressant relating those concentrations to drug dosing and clinical events. Although this traditional approach is able to identify environmental and nongenetic factors that can influence drug exposure during the course of treatment, it presents limitations. Therefore, complementary strategies are advocated. The advent of the genomic era gives birth to pharmacogenomics, a science that studies how the genome as a whole, including single genes as well as gene-to-gene interactions, may affect the action of a drug. This science is of particular importance for drugs characterized by a narrow therapeutic index, such as the immunosuppressants. Preliminary studies focused on polymorphisms of genes encoding for enzymes actively involved in drug metabolism, drug transport and pharmacological target. Pharmacogenomics holds promise for improvement in the ability to individualize immunosuppressive therapy based on the patient's genetic profile, and can be viewed as a support to traditional therapeutic drug monitoring. However, the clinical applicability of this approach is still to be proven.

The drugs don't work: expectations and the shaping of pharmacogenetics

This article examines one particular set of technologies arising from developments in human genetics, those aimed at improving the targeting, design and use of conventional small molecule drugs-pharmacogenetics. Much of the debate about the applications and consequences of pharmacogenetics has been highly speculative, since little or no working technology is yet on the market. This article provides a novel analysis of the development of pharmacogenetics, and the social and ethical issues it raises, based on the sociology of technological expectations. In particular, it outlines how two alternative visions for the development of the technology are being articulated and embedded in a range of heterogeneous discourses, artefacts, actor strategies and practices, including: competing scientific research agendas, experimental technologies, emerging industrial structures and new ethical discourses. Expectations of how pharmacogenetics might emerge in each of these arenas are actively shaping the trajectory of this nascent technology and its potential socio-economic consequences.

Pharmacogenetics and psychopharmacotherapy

Response to drugs can vary between individuals and between different ethnic populations. The biological (age, gender, disease and genetics), cultural and environmental factors which contribute to these variations are considered in this review. The most important aspect is the genetic variability between individuals in their ability to metabolize drugs due to expression of 'polymorphic' enzymes. Polymorphism enables division of individuals within a given population into at least two groups, poor metabolisers (PMs) and extensive metabolisers (EMs) of certain drugs. The two most extensively studied genetic polymorphisms are those involving cytochrome P450 2D6 (CYP2D6) and CYP2C19. CYP2D6 metabolizes a number of antidepressants, antipsychotics, beta-adrenoceptor blockers, and antiarrhythmic drugs. About 7% of Caucasians and 1% of Asians are PMs of CYP2D6 substrates. CYP2C19 enzyme participates in the metabolism of omeprazole, propranolol and psychotropic drugs such as hexobarbital, diazepam, citalopram, imipramine, clomipramine and amitriptyline. The incidence of PMs of CYP2C19 substrates is much higher in Asians (15-30%) than in Caucasians (3-6%). Variations in metabolism of psychotropic drugs result in variations in their pharmacokinetic parameters. This may lead to clinically significant intra- and inter-ethnic differences in pharmacological responses. Such variations are discussed in this review. Differential receptor-mediated response may play a role in ethnic differences in responses to antipsychotics and tricyclic antidepressants, but such pharmacodynamic factors remain to be systematically investigated. The results of studies of ethnic differences in response to psychopharmacotherapy appear to be discrepant, most probably due to limitations of study design, small sample size, inadequately defined study sample, and lack of control of confounding factors. The clinical value of understanding pharmacogenetics is in its use to optimize therapeutic efficacy, to prevent toxicity of those drugs whose metabolism is catalysed by polymorphic isoenzymes, and to contribute to the rational design of new drugs. Finally, applications and impact of pharmacogenetics in the field of psychopharmacotherapy are discussed.

From genes to public health: the applications of genetic technology in disease prevention. Genetics Working Group

OBJECTIVES

With advances in the Human Genome Project, the implications of genetic technology in disease prevention should be assessed.

METHODS

The paradigm suggested in The Future of Public Health--assessment, policy development, and assurance--was used to examine the continuum from genetic technology to public health practice.

RESULTS

First, important public health functions are to (1) assess the impact of genes and their interactions with modifiable disease risk factors on the health status of the population and (2) assess the impact and safety of genetic testing on the population. Second, given the many implications of genetic testing, the public health community should participate in policy development related to the timing and use of genetic testing in disease prevention. Third, whenever appropriate, the public health community needs to ensure the development of public health genetics programs (e.g. newborn screening) and evaluate the quality and effectiveness of the use of genetic testing in disease prevention.

CONCLUSIONS

Although most current genetic tests are not ready for disease prevention, there is an important role for the public health community in translating genetic technology into disease prevention.

Theory and practice of psychopharmacogenetics

This article attempts to elucidate the theory and practice of psychopharmacogenetics. Eight working models were identified and characterized with a distinct view of risk factors in the host, the pathophysiology of disease, and the strategies for optimum therapy. The biochemical culprits related to adverse drug reaction in each case can be used to identify a risk and thus contribute to prevention research. Since the phenomenology of these uncommon conditions covers a broad spectrum of neuropsychiatric manifestations, the insights they generated might presage a better understanding of the natural history of a wider range of mental disorders associated with genetic vulnerability. The emerging information suggests that psychopharmacogenetics could be defined from clinical perspectives as multidimensional analysis of genes, drugs, and behaviour for the treatment and prevention of psychiatric disorders.

Structure-function relationship studies in human cholinesterases reveal genomic origins for individual variations in cholinergic drug responses

1. Due to their involvement in the termination of neurotransmission at cholinergic synapses and neuromuscular junctions, cholinesterases are the target proteins for numerous drugs of neuro-psychopharmacology importance. 2. In order to perform structure-function relationship studies on human cholinesterases with respect to such drugs, a set of expression vectors was engineered, all of which include cloned cDNA inserts encoding various forms of human acetyl- and butyrylcholinesterase. These vectors were designed to be transcribed in vitro into their corresponding mRNA products which, when microinjected into Xenopus oocytes, are efficiently translated to yield their catalytically active enzymes, each with its distinct substrate specificity and sensitivity to selective inhibitors. 3. A fully automated microtiter plate assay for evaluating the inhibition of said enzymes by tested cholinergic drugs and/or poisons has been developed, in conjunction with computerized data analysis, which offers prediction of such inhibition data on the authentic human enzymes and their natural or mutagenized variants. 4. Thus, it was found that asp70-->gly substitution renders butyrylcholinesterase succinylcholine insensitive and resistant to oxime reactivation while ser 425-->Pro with gly70 gives rise to the "atypical" butyrylcholinesterase phenotype, abolishing dibucaine binding. 5. Furthermore, differences in cholinesterase affinities to physostigmine, ecothiophate and bambuterol were shown in these natural variants. 6. Definition of key residues important for drug interactions may initiate rational design of more specific cholinesterase inhibitors, with fewer side effects. This, in turn, offers therapeutic potential in the treatment of clinical syndromes such as Alzheimer's and Parkinson's disease, glaucoma and myasthenia gravis.

Psychopharmacogenetic aspects of Prader-Willi syndrome

The study of genes, drugs, and behavior in three male adolescents with Prader-Willi syndrome (PWS) revealed a clinical profile that raises questions about the indications for neuroleptic and appetite-suppressing medications in this condition. Evidence of the inadvisability of neuroleptic medication and of the pathophysiology of PWS has led to a remarkable control of violent outbursts and hyperphagia by carbamazepine in one patient afflicted with both PWS and Klinefelter's syndrome. Testosterone and behavioral therapy proved to be useful in the management of two patients. The present observations, which are supported by recent advances in the pathophysiology of satiety, suggest that PWS should be understood as a metabolic disorder and subjected to psychopharmacogenetic study.