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Edited by
Allan Young, Institute of Psychiatry, King's College London,Marsal Sanches, Baylor College of Medicine, Texas,Jair C. Soares, McGovern Medical School, The University of Texas,Mario Juruena, King's College London
Due to the chronic relapsing nature of mental disorders and increased life expectancy, the societal burden of these non-communicable diseases will increase. Treatments for mental disorders are available, but their effect is limited due to patients’ (genetic) heterogeneity, low treatment compliance and frequent side effects. Today, medication selection in psychiatry relies on a trial-and-error approach based mainly on physicians’ experience. Pharmacogenetic testing can help in this process by determining the person-specific genetic factors that may predict clinical response and side effects associated with genetic variants that impact drug-metabolizing enzymes, drug transporters or drug targets .
Pharmacogenetics is a discipline that investigates genetic factors that affect the absorption, metabolism, and transport of drugs, thereby affecting therapy outcome. These genetic factors can, among other things, lead to differences in the activity of enzymes that metabolize drugs. Recent studies in depressed patients show that genotyping of drug-metabolizing enzymes can increase the effectiveness of treatment, which could benefit millions of patients worldwide.
Sialorrhea is a common and uncomfortable adverse effect of clozapine, and its severity varies between patients. The aim of the study was to select broadly genes related to the regulation of salivation and study associations between sialorrhea and dry mouth and polymorphisms in the selected genes.
Methods:
The study population consists of 237 clozapine-treated patients, of which 172 were genotyped. Associations between sialorrhea and dry mouth with age, sex, BMI, smoking, clozapine dose, clozapine and norclozapine serum levels, and other comedication were studied. Genetic associations were analyzed with linear and logistic regression models explaining sialorrhea and dry mouth with each SNP added separately to the model as coefficients.
Results:
Clozapine dose, clozapine or norclozapine concentration and their ratio were not associated with sialorrhea or dryness of mouth. Valproate use (p = 0.013) and use of other antipsychotics (p = 0.015) combined with clozapine were associated with excessive salivation. No associations were found between studied polymorphisms and sialorrhea. In analyses explaining dry mouth with logistic regression with age and sex as coefficients, two proxy-SNPs were associated with dry mouth: epidermal growth factor receptor 4 (ERBB4) rs3942465 (adjusted p = 0.025) and tachykinin receptor 1 (TACR1) rs58933792 (adjusted p = 0.029).
Conclusion:
Use of valproate or antipsychotic polypharmacy may increase the risk of sialorrhea. Genetic variations in ERBB4 and TACR1 might contribute to experienced dryness of mouth among patients treated with clozapine.
In the years following FDA approval of direct-to-consumer, genetic-health-risk/DTCGHR testing, millions of people in the US have sent their DNA to companies to receive personal genome health risk information without physician or other learned medical professional involvement. In Personal Genome Medicine, Michael J. Malinowski examines the ethical, legal, and social implications of this development. Drawing from the past and present of medicine in the US, Malinowski applies law, policy, public and private sector practices, and governing norms to analyze the commercial personal genome sequencing and testing sectors and to assess their impact on the future of US medicine. Written in relatable and accessible language, the book also proposes regulatory reforms for government and medical professionals that will enable technological advancements while maintaining personal and public health standards.
In Alzheimer’s disease (AD), angiotensin II receptor blockers (ARBs) could reduce cerebrovascular dysfunction, while angiotensin-converting enzyme inhibitors (ACEis) might increase brain amyloid-β by suppressing effects of the angiotensin-converting enzyme 1, an amyloid-β-degrading enzyme. However, ACEis could benefit patients with AD by reducing the amyloidogenic processing of the amyloid precursor protein, by central cholinergic and anti-inflammatory mechanisms, and by peripheral modulation of glucose homeostasis. We aimed to investigate whether the ACE insertion/deletion polymorphism is associated with clinical changes in patients with AD, while considering apolipoprotein E (APOE)-ϵ4 carrier status and blood pressure response to angiotensin modulators.
Methods:
Consecutive outpatients with late-onset AD were screened with cognitive tests and anthropometric measurements, while their caregivers were queried for functional and caregiver burden scores. Prospective pharmacogenetic associations were estimated for 1 year, taking APOE-ϵ4 carrier status and genotypes of the ACE insertion/deletion polymorphism into account, along with treatment with ACEis or ARBs.
Results:
For 193 patients (67.4% women, 53.4% APOE-ϵ4 carriers), the ACE insertion/deletion polymorphism was in Hardy–Weinberg equilibrium (p = 0.281), while arterial hypertension was prevalent in 80.3% (n = 124 used an ACEi, n = 21 used an ARB). ARBs benefitted mostly APOE-ϵ4 carriers concerning caregiver burden variations, cognitive and functional decline. ACEis benefitted APOE-ϵ4 non-carriers concerning cognitive and functional decline due to improved blood pressure control in addition to possible central mechanisms. The ACE insertion/deletion polymorphism led to variable response to angiotensin modulators concerning neurological outcomes and blood pressure variations.
Conclusion:
Angiotensin modulators may be disease-modifiers in AD, while genetic stratification of samples is recommended in clinical studies.
The purpose of this research was to determine the frequency of mutation of the cytochrome CYP3A5 genes and transport proteins SLCO1B1 and MDR1 in patients with coronary heart disease in the Kazakh nation. A prospective cohort clinical and genetic study was conducted. The study was conducted in 2017−2019. Medical records containing information about drug prescription conducted in hospitals and outpatient departments were carefully analyzed. In the examined group of 178 patients treated with statins, a significant frequency of genetic variants that determine the increased risk of complications of statin use was revealed. There was a tendency toward an increase in the activity of creatine phosphokinase (CPK) in the blood upon detection of the A6986G mutation of the cytochrome gene and SLCO1B1 (c.521T>C) gene of the transport protein OATP1B1. In the studied Kazakh population, the presence of a homozygous mutant SLCO1B1 gene of the transport protein can be recommended as a genetic marker for the undesirability of using antihypercholesterolemic therapy with statins, which simultaneously leads to a decrease in the effectiveness of treatment and an increase in the risk of side effects.
So far, this book has focused on cognitive aspects of the mind. This chapter introduces the emerging area of affective science and emotion studies, which has gathered impetus in recent years. The first section reviews early theories of human emotions from Herbert Simon and Paul Ekman. The second section looks at how affective scientists explore emotions from a multidimensional perspective, introducing some new techniques in affective neuroscience. The last section draws the different strands together through the case study of fear, looking in particular at the neurobiology and neuroscience of fear.
An ever-expanding annotation of the human genome sequence continues to promise a new era of precision medicine. Advances in knowledge management and the ability to leverage genetic information to make clinically relevant, predictive, diagnostic, and targeted therapeutic choices offer the ability to improve patient outcomes and reduce the overall cost of healthcare. However, numerous barriers have resulted in a modest start to the clinical use of genetics at scale. Examples of successful deployments include oncologic disease treatment with targeted prescribing; however, even in these cases, genome-informed decision-making has yet to achieve standard of care in most major healthcare systems. In the last two decades, advances in genetic testing, therapeutic coverage, and clinical decision support have resulted in early-stage adoption of pharmacogenomics – the use of genetic information to routinely determine the safety and efficacy profile of specific medications for individuals. Here, through their complicated histories, we review the current state of pharmacogenomic testing technologies, the information tools that can unlock clinical utility, and value-driving implementation strategies that represent the future of pharmacogenomics-enabled healthcare decision-making. We conclude with real-world economic and clinical outcomes from a full-scale deployment and ultimately provide insight into potential tipping points for global adoption, including recent lessons from the rapid scale-up of high-volume test delivery during the global SARS-CoV2 epidemic.
Depression in pregnancy is common and often requires treatment with antidepressant drugs. Most antidepressants are metabolized by the cytochrome P450 system (CYP), in particular CYP2C19 and -2D6, both of which are genetically polymorphic. Additionally, the activity of these enzymes is altered during pregnancy.
Objectives
To investigate pharmacogenetic variability regarding CYP2C19 and -2D6 in pregnant users of antidepressants and treatment outcomes.
Methods
The study population comprises all women born between 1981-1999, who gave birth to at least one child before December 2015 identified from the large Danish population-based iPSYCH2012 case-cohort study sample linked to information on genetic variants, prescription drug use and outcome data. Pharmacogenetic genotypes and phenotypes of CYP2C19 and CYP2D6 will be categorized into poor, (PM), intermediate, (IM), extensive, (EM), rapid (RM) and ultra-rapid metabolizers (RM) using array-based SNP information. Antidepressant drug use and comedication during pregnancy will be assessed based on prescription data. Outcomes include treatment discontinuation, switching and psychiatric hospitalizations. Cox regression analysis will be performed to estimate the hazard ratios comparing the rates of the different outcomes in people with different phenotypes, compared with EM adjusted for a number of confounding factors.
Results
Based on previous research we will be able to identify approximately 6531 pregnant women with a psychiatric history. Among those, we estimate to find 14 PM, 161 IM, 285 EM, 168 RM and 25 UM of CYP2C19, and 27 PM, 218 IM and 408 EM of CYP2D6. Exposure to antidepressants is estimated at 10%.
Conclusions
We expect to be able to present the results at the conference.
There are relatively fewer pharmacogenetic studies of antipsychotics in adolescents than in adult patients. The development of personalized pharmacotherapy is promising.
Objectives
Identify the most significant pharmacogenetic predictors of antipsychotic safety in adolescents experiencing acute psychotic episodes
Methods
The study included 101 adolescents diagnosed with acute polymorphic psychotic disorder at the time of admission (F23.0-9 according to ICD-10). All patients were taking an antipsychotic as their main treatment for 14 days. Children’s Global Assessment Scale (CGAS), Positive and Negative Symptoms Scale (PANSS), Clinical Global Impression Severity (CGI-S) and Improvement (CGI-I), UKU Side Effects Rating Scale (UKU SERS), Sympson-Angus Scale (SAS), Barnes Akathisia rating scale (BARS) were used. All study participants underwent pharmacogenetic testing of pharmacokinetic and pharmacodynamic factors.
Results
CYP2D6 “intermediate” metabolism increased the risk of developing an adverse reaction by a trend of significance (OR=2.616 (95% CI 0.950-7.203); p=0.063). Carriage of HTR2A rs6313 was associated with a lower score on the UKU SERS “Other Symptoms” subscale (Beta=(-0.289); p=0.003) and an objective score on the BARS akathisia severity scale (Beta=(-0.217); p=0.029). DRD3 rs324026 carriers had a lower BARS akathisia scale score (Beta=(-0.349); p=0.004); DRD3 rs6280 carriers had a lower SAS extrapyramidal symptom severity scale score (Beta=(-0.351); p=0.003). Carriers of ANKS1B rs7968606 were associated with a higher SAS scale score (Beta=0.237; p=0.017).
Conclusions
We proposed that genotyping of CYP2D6*4, *10, DRD3 rs324026 (C allele), DRD3 rs6280 (C allele), HTR2A rs6313 (TT genotype) and ANKS1B rs7968606 (T allele) will predict the high risk of intolerance to antipsychotics in adolescents with acute psychotic episodes.
Pharmacogenetic (PGx) targets to optimize drug therapy, but its implementation is rare.
Objectives
We evaluate the clinical utility of PGx testing in psychiatry by investigating the one-year risks of clinical outcomes in patients with depression taking sertraline, (es)citalopram or fluoxetine by their Cytochrome P450 (CYP) 2C19/2D6 phenotypes.
Methods
We investigated 17,297 individuals born between 1981-2005 with a depression diagnosis between 1996-2012 from the iPsych2012 case-cohort. Based on array-based single-nucleotide-polymorphism genotype data, individuals were phenotyped as CYP2C19/CYP2D6 normal (NM, reference group), ultra-rapid- (UM), rapid- (RM), intermediate- (IM), or poor-metabolizer (PM). Outcomes were treatment switching or discontinuation, psychiatric in-, out-, and emergency room contacts (ER), and suicide attempt/self-harm. Incidence rate ratios (IRR) by age groups were estimated using Poisson regression analysis with 95% confidence intervals, adjusted for potential confounders.
Results
Risks of switching (IRR=1.89[1.22-2.93]), ERs (1.69 [1.01-2.81]) and suicide attempt/self-harm (2.73 [1.49-5.01]) were higher in CYP2C19 PMs <19 years taking (es)citalopram. Fluoxetine users <19 years had a decreased risk of discontinuation in CYP2D6 PMs (0.5 [0.27-0.95]) and decreased risk of out-patient contacts in CYP2D6 PMs and IMs (IRRIM=0.83 [0.68-1.00] and IRRPM=0.59 [ 0.37-0.96]). We observed an increased risk for ERs in CYP2D6 PMs aged 19-25 years taking fluoxetine (4.53 [1.54-13.35]). In CYP2C19 UMs >25 years taking (es)citalopram the risk of suicide attempt/self-harm was more than three-fold increased (3.64 [ 1.01-13.19]). We found no significant results in users of sertraline.
Conclusions
PGx variability was associated with treatment outcomes in depression in patients with CYP2C19 PM or UM status taking (es)citalopram, or CYP2D6 PM or IM status taking fluoxetine.
Direct-to-consumer (DTC) genetic testing has raised questions about the accuracy of the test results, which may raise potential novel liability issues. This chapter examines potential liability exposures relating to DTC genetic testing in two main contexts. The first is potential liability for the DTC provider itself for erroneous results. Key issues in such cases will be the validity and effect of the representations and disclosures that the DTC company provides, which often informs the consumer that the results should not be relied on for medical care, disclaim any liability for any harms that may result from such reliance, and require any disputes to be resolved by mandatary arbitration. The second potential type of case is against health care providers who are presented with DTC results by their patients. Providers will often be put in a “damned if they do, damned if they don’t” predicament by such results, as both ignoring or relying on the DTC test results could create potential liabilities in certain situations. While providers can usually protect themselves by requiring validation of the DTC results by an independent laboratory, time and economic constraints may make this infeasible in some cases.
Pharmacogenetics (PGx) studies genetic variance and related differences in drug outcomes. PGx guidelines for psychotropic drugs are available (PGx drugs). By executing PGx testing in a prospective or pre-emptive setting, dose adjustments or even change of treatment type can be applied prior to start of therapy to patients who carry a specific geno- or phenotype (i.e. actionable geno- or phenotypes). By doing so, increased efficacy of therapy or reduced risk of adverse events of treatment can be accomplished. In Denmark, broad implementation of PGx is currently still low.
Objectives
The aim of this study is to classify the PGx profiles of Danish individuals with and without severe mental disorders (SMD), to be used in follow-up studies investigating PGx and drug outcomes.
Methods
This study made use of imputed genotyping data of the Danish iPSYCH sample, which includes 77,639 young individuals born between 1981-2005, with or without a diagnosis of one or more of five selected SMD (i.e. depression, attention-deficit/hyperactivity disorder, autism, bipolar disorder and schizophrenia). We investigated a panel of 48 genetic variants with known PGx applications (part of the U-PGx consortium, a Horizon2020 funded project on clinical relevant PGx in the EU).
Results
Imputed data contains over 11 million SNPs of 77,639 individuals.
Conclusions
We expect results in the end of 2020.
Disclosure
We thank the iPSYCH consortium, in specific the iPSYCH PI’s (Merete Nordentoft, Anders Børglum, Preben B. Mortensen, Ole Mors, Thomas Werge and David M. Hougaard). The iPSYCH project is funded by the Lundbeck Foundation Denmark and the universities and un
Pharmacogenetics (PGx) studies genetic variance and related differences in drug outcomes. The aim of PGx testing is to increase therapy efficacy and safety, by applying e.g. dose adjustments in patients with a specific geno- or phenotype. PGx guidelines for psychotropic drugs are available (PGx drugs), including atomoxetine used in the treatment of attention deficit hyperactivity disorder (ADHD). In Denmark, broad implementation of PGx is currently still low, possibly due to the lack of population-based studies investigating the real-world impact of PGx variability.
Objectives
The aim of this study is to investigate the association of PGx variability (patients’ genotype/phenotype) in users of atomoxetine and different treatment outcomes in a large population-based sample of individuals with ADHD.
Methods
This study will use data of the large Danish population-based iPSYCH case-cohort study sample including information on genetic variants, prescription drug use and outcome data, e.g. psychiatric and somatic hospitalizations and death. The study population comprises all individuals diagnosed with ADHD born 1981-2005 with at least one prescription for atomoxetine between 1995 and 2016. All individuals will be categorized according to their CYP2D6 phenotypes. We will perform Cox regression analysis to estimate the hazard ratios comparing the rates of the different outcomes in people with different phenotypes adjusted for a number of confounding factors.
Results
We have identified approximately 20,000 individuals with ADHD, of whom an estimated 10-20% have filled at least one prescription of atomoxetine.
Conclusions
We expect results in the beginning of 2021.
Disclosure
We thank the iPSYCH consortium, in specific the iPSYCH PI’s (Merete Nordentoft, Anders Børglum, Preben B. Mortensen, Ole Mors, Thomas Werge and David M. Hougaard). The iPSYCH project is funded by the Lundbeck Foundation Denmark and the universities and un
Schizophrenia is one of the most severe mental disorders. Haloperidol and other first-generation antipsychotics are widely used for schizophrenia treatment, but have prominent side effects, primarily extrapyramidal symptoms (EPS). The EPS severity is highly variable and may be underlied by genetic factors.
Objectives
We performed a prospective study to test the association of DRD2/ANKK1 Taq1A polymorphism (rs18000497) and CYP2D6 phenotype, predicted from genotypes using 8 CYP2D6 alleles (*3, *4, *5, *6,*9, *10,*41, xN) with EPS severity during haloperidol treatment in schizophrenia spectrum disorders patients.
Methods
57 inpatients with schizophrenia spectrum disorders (42,1% females; mean age - 46,7±11,8 y.o (M±SD) of European ancestry were enrolled in the study. Abnormal Involuntary Movement Scale (AIMS), Barnes Akathisia Rating Scale (BARS), Simpson-Angus Scale (SAS) were used to assess EPS on two timepoints: day 1 and day 21 of haloperidol treatment.
Results
TaqIA T-allele carriers in contrast to wild-type allele homozygous patients had higher scores of BARS (p=0.029) and SAS (p=0.024) on day 21. After stratification by CYP2D6 phenotype, these differences were observed only in extensive metabolizers (p=0.006 and p=0.001 respectively), although the CYP2D6 phenotype itself was not associated with EPS severity. The combined effect of TaqIA T allele with CYP2D6 extensive phenotype on BARS score on day 21 was confirmed by General Linear Model (p=0.013).
Conclusions
Our results show that minor TaqIA T-allele is associated with the severity of EPS after 3 weeks of haloperidol treatment only in CYP2D6 extensive metabolizers. That highlights the importance of using both pharmacokinetic and pharmacodynamic genetic markers in pharmacogenetic EPS risk assessment.
Pharmacogenetics (PGx) studies genetic variance and related differences in drug outcomes. PGx guidelines for psychotropic drugs are available (PGx drugs), but PGx testing is used only limitedly in psychiatric clinical practice.
Objectives
The aim of this study is to pinpoint different aspects of PGx drug use in the population, to support clinical uptake of PGx.
Methods
This drug utilization study investigated prescription PGx drug use in 56,065 young individuals with different severe mental disorders (SMD) in the Danish iPSYCH sample (born 1981-2005). We investigated the number of PGx drug users (incidence, prevalence), age (at first PGx drug use), sex, multiple PGx drugs per user (in light of panel-based PGx testing) and concomitant use of PGx drugs (in light of combinatorial PGx testing).
Results
We identified substantial PGx drug use in terms of incidence rates (e.g. 333 per 10,000 person years for the anticonvulsant lamotrigine) and prevalence (e.g. 15,260 users for the antidepressant citalopram) in patients with SMD. The age of first time PGx drug use ranged from 11.6-20 years, depending on SMD and sex. On average, more than one PGx drug was used by a single person (range 1.6-5.6 drugs, depending on SMD) or even used concomitantly (41-69%) affecting mostly two different PGx genes (84-92% of concomitant PGx drug users).
Conclusions
PGx drugs were frequently used in young individuals with SMD, often subsequently and concomitantly, arguing for panel-based/combinatorial PGx testing over single-gene testing. PGx testing could be applied already at a very young age.
Disclosure
We thank the iPSYCH consortium, in specific the iPSYCH PI’s (Merete Nordentoft, Anders Børglum, Preben B. Mortensen, Ole Mors, Thomas Werge and David M. Hougaard). The iPSYCH project is funded by the Lundbeck Foundation Denmark and the universities and un
Pharmacogenetic influences on therapeutic response to e.g. antidepressant or neuroleptic treatment are poorly understood and the lack of efficacy in many of the patients together with side effects can both limit therapy and compliance. Thus the aim of pharmacogenetics and pharmacogenomics is to provide predictive tools for the response to psychopharmacologic agents in the therapy of psychiatric disorders and in that ways to provide a real personalized psychiatry. The following review will summarize the current stage of pharmacogenetics and pharmacogenomics and will critically discuss the possibilities of a personalized medicine.
Antipsychotics often induce excessive weight gain. We hypothesised that individuals with genetic variations related to known obesity-risk genes have an increased risk of excessive antipsychotic-induced weight gain (AIWG). This hypothesis was tested in a subset of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) trial data set.
Methods:
The CATIE trial compared effects and side effects of five different antipsychotics through an 18-month period. Based on the maximum weight gain recorded, excessive weight gain was defined as >7% weight gain. Cytoscape and GeneMANIA were instrumental in composing a molecular pathway from eight selected genes linked to obesity. Genetic information on a total of 495.172 single-nucleotide polymorphisms (SNPs) were available from 765 (556 males) individuals. Enrichment test was conducted through ReactomePA and Bioconductor. A permutation test was performed, testing the generated pathway against 105 permutated pathways (p ≤ 0.05). In addition, a standard genome-wide association study (GWAS) analysis was performed.
Result:
GWAS analysis did not detect significant differences related to excessive weight gain. The pathway generated contained 28 genes. A total of 2067 SNPs were significantly expressed (p < 0.01) within this pathway when comparing excessive weight gainers to the rest of the sample. Affected genes including PPARG and PCSK1 were not previously related to treatment-induced weight gain.
Conclusions:
The molecular pathway composed from high-risk obesity genes was shown to overlap with genetics of patients who gained >7% weight gain during the CATIE trial. This suggests that genes related to obesity compose a pathway of increased risk of excessive AIWG. Further independent analyses are warranted that may confirm or clarify the possible reasoning behind.
The burden of communicable and non-communicable diseases in Sub-Saharan Africa poses a challenge in achieving quality healthcare. Although therapeutic drugs have generally improved health, their efficacy differs from individual to individual. Variability in treatment response is mainly because of genetic variants that affect the pharmacokinetics and pharmacodynamics of drugs.
Method.
The intersection of disease burden and therapeutic intervention is reviewed, and the status of pharmacogenomics knowledge in African populations is explored.
Results.
The most commonly studied variants with pharmacogenomics relevance are discussed, especially in genes coding for enzymes that affect the response to drugs used for HIV, malaria, sickle cell disease and cardiovascular diseases.
Conclusions.
The genetically diverse African population is likely to benefit from a pharmacogenomics-based healthcare approach, especially with respect to reduction of drug side effects, and separation of responders and non-responders leading to optimized drug choices and doses for each patient.
We investigated the association between clinical outcome and the recommendations of a pharmacogenetic test (Neuropharmagen) in patients with a variety of psychiatric conditions whose previous treatment regimen had failed.
Methods
This retrospective, naturalistic, multicenter study included adult psychiatric patients (depression, psychosis, anxiety, bipolar, etc.) who had been seen at 3 private clinics. All patients had received pharmacogenetic testing (Neuropharmagen) and were classified depending on whether or not their post-test treatment regimen followed the test recommendations. Clinical severity was assessed with the Clinical Global Impression of Severity (CGI-S) at baseline (pre-test) and 3-month follow-up, and adverse events were recorded.
Results
182 patients were available for analysis. After multivariate adjustment, patients whose treatment followed the test recommendations had odds of improvement about 4 times greater than patients whose treatment did not follow the recommendations (adjusted OR=3.86, 95%CI 1.36–10.95; p=0.011). Importantly, psychiatric diagnosis did not significantly affect the odds of improvement. Also, in the subpopulation with baseline CGI-S score >3 (N=170), the rate of stabilization at follow-up (defined as CGI-S≤3) was significantly higher in patients whose treatment followed the pharmacogenetic recommendations (p=0.033). There was no apparent difference in the incidence of adverse events (6 patients in each group).
Conclusions
Non–drug naïve patients whose treatment followed the recommendations of pharmacogenetic testing were more likely to improve their condition than patients whose treatment did not. These results are consistent with previous clinical research on depressed patients, and this study also suggests that this benefit can be extended to psychiatric conditions other than depression.
A great interindividual variability exists in biological response to drugs. This variability is partly attributable to pharmacodynamic factors (drug - receptor interactions) and partly to pharmacokinetic factors. Drugs can be eliminated from the body by renal clearance, metabolism or both. Although every tissue has some ability to metabolise xenobiotics like drugs, the liver is the principal organ of biotransformation. Major metabolising enzymes are the cytochrome-P450 mono-oxygenases, epoxide hydrolase, glucuronosyl-transferase, acetyl-transferase, sulfo-transferase and xanthine oxidase. Some of these enzymes display in a subset of subjects a ‘normal’ activity and in another subset of subjects a reduced or a greatly increased activity. This altered activity may be genetically determined and is then called genetic polymorphism. Clinically relevant metabolic differences traditionally have been defined by their genotypie expression such as ‘poor’ and ‘extensive’ metaboliser. The recent developments of powerful methods for DNA (or genomic) analysis portends a revolutionary expansion of our understanding of physiology as well as pathology. Pharmacogenetics is the study of genetic variation underlying differential response to drugs. Genotyping may become a useful tool in optimising drug treatment. Another part of the genetic research is directed towards the discovery of genetic alterations leading to diseases. Once identified, these genetic alterations can become targets for drug treatment (e.g. gene therapy). Pharmaco-genomics applies the large-scale systematic approaches of genomics to speed the discovery of drug response markers, whether they act at the level of the drug target, drug metabolism or disease pathway. Table I gives some examples of genetic alterations that are identified together with their effects. Some of these examples will be briefly discussed here.