Pharmacocogenetics In Forensic Sciences

The completion of Human Genome Project and advancement of analytical technology with  the large-scale identification of genome polymorphisms have contributed to the field of forensic science, especially in the studies on genetic basis of most important inherited arrhythmia syndromes responsible to sudden cardiac death, a major cause of death worldwide, and of individual differences in response to potential toxicants, with a new emerging area of interest, the so called pharmacogenetics. One of the goals of pharmacocogenetics is the identification of the molecular genetic bases for interindividual variations in susceptibility to the anticipated effects of a drug or of xenobiotics. There is no doubt that adverse drug reactions (ADRs) are a common cause of morbidity and mortality, despite extensive and well-regulated registration processes for proving drug efficacy and drug safety, and are associated with substantial costs of medical care. Genetic studies could also clarify the origins of addictions, a diverse set of common, complex diseases, that are to some extent tied together by shared genetic and environmental etiological factors. The use and abuse of legal and illegal substances is a worldwide public health priority with repercussions extending from the level of the individual to the family, community, and society. Any substance that is capable of producing a therapeutic effect can also produce unwanted or adverse effects; the risk of such effects ranges from near zero to high. An adverse drug reaction (ADR), according to the World Health Organization definition, is “a response to a drug that is noxious, unintended, and undesired effect of a drug, which occurs at doses used in man for prophylaxis, diagnosis, or therapy of disease, or for modification of physiological function”. This definition excludes therapeutic failures, intentional and accidental poisoning (ie, overdose), and drug abuse. Also, this does not include adverse events due to errors in drug administration or non-compliance (taking more or less of a drug than the prescribed amount); using this narrow definition avoids overestimating the ADR incidence. The terms adverse reaction and adverse effect are interchangeably, but must be kept in mind that is the “drug” that has an adverse effect whereas it is the “patient” that experience an adverse reaction. However, the two terms must be distinguished from “adverse event”, that is an averse outcome that occurs while a patient is taking a drug, but is not necessarily attributable to it. The occurrence of ADRs is associated with morbidity and mortality and substantial costs of medical care. Numerous studies provide a wide range of epidemiological data regarding adverse drug reactions. ADRs are one of the top ten causes of death in the United States, causing over 100 000 deaths annually; approximately 2–5% of all hospital admissions can be attributed to adverse drug reactions. Unfortunately, many physicians still consider adverse drug reactions to be an exception, rather than a primary diagnosis and adverse drug reactions have become cases of medical professional liability, with great increase of lawsuits. Potential risk factors for ADRs include patients’ age, sex, race, nutritional status, organ function, especially of liver and kidneys, co-morbidities, co-medication, as well as some lifestyle variables (smoking habits, concomitant use of alcohols and drugs) and, of course, genetics. Some ADRs caused by genetic variation, previously considered unpredictable, may now be preventable. In general, genetic factors are estimated to account for 15-30% of interindividual differences in drug metabolism and response, but for certain drugs this can be as high as 95%. ADRs may be reduced by means of the introduction of “personalized medicine”, which anticipates the screening of patients for polymorphisms associated with a drug response, usually performed prior to the initiation of therapy. Despite significant progress in this field, only few drugs, such as cetuximab, dasatinib, maraviroc and trastuzumab, require a pharmacogenetic test before being prescribed: there are several gaps that limit the application of pharmacogenetics based upon the complex nature of the drug response itself. This kind of policy foresees the introduction of new sophisticated tests, especially in the field of genetics, like DNA microarrays or DNA chips. Drug addiction is a chronic, relapsing disorder in which compulsive drug-seeking and drugtaking behavior persists despite serious negative consequences; continued use induces adaptive changes in the central nervous system that lead to tolerance, physical dependence, sensitization, craving, and relapse. This mental health disorder imposes a significant burden on those directly affected, health care systems, and society in general, since it is associated with considerable morbidity and mortality, violence, and legal issues. Polydrug use of psychoactive substances, legal and illegal, characterizes and defines the style of consumption prevailing more and more common among younger subjects. There is another emerging market worldwide for an increasing number of psychoactive substances whose compositions are not well known and whose effects have not yet been recorded by physicians and they are difficult to recognize, delaying the diagnosis and treatment of patients themselves. In addition there is another phenomenon in recent years: it is a marked shift in the marketing of licit and illicit drugs through online pharmacies, without requiring a prescription. The new generations are particularly vulnerable to this risk because they are very prone to use new technologies. The several classes of medications that are commonly abused include: analgesics opioids, which are most often prescribed to treat severe pain (morphine, oxycodone, hydrocodone, hydromorphone, codeine); central nervous system depressants, commonly prescribed to treat anxiety and sleep disorders (barbiturates and benzodiazepines); stimulants, which are used primarily to treat attention defict disorder, attention defict hyperactivity disorder (ADHD) and narcolepsy (dextroamphetamine and methylphenidate). The OTC medicines, such as certain cough suppressant (dextromethorphan), sleep aids (doxylamine), antihistamines (diphenhydramine), decongestants and others can be abused for their psychoactive effects. The current challenge is to transfer the important increase of the knowledges of addiction's neurobiology in patients with addiction problems and to identify specific genes responsible for the particular vulnerability or resistance to addiction. Some schools of thought contend that addiction is entirely preventable through proper legislative action and individual choice, and claim that genetic research in this field is to assume a role as a low priority. The genetic influences are more prominent in the later phases of individuals’ progression toward substance dependence; this variation could add to allelic variations that could produce effects on addiction susceptability phenotypes by other routes that could include: differences in pharmacokinetic characteristics of the substance such as metabolism and biodistribution; differences in drug’s rewarding properties; differences in traits manifest by the addict, including personality differences; differences in addict’s psychiatric comorbidities. Individuals are all different from each other and much of this difference has a genetic basis. Two unrelated human beings also share 99.9% of their genomic sequence, and could be considered genetically almost identical: the difference has been estimated to be of 0.1% overall, but still, this means that there are at least several million nucleotide differences per individual. There are, on average, three million genetic differences between any two people; the human genome contains approximately 3 billion base pairs of DNA and the variability of genetic material between any two individuals averages approximately one variation for every 1,000. different susceptibility to induce adverse health effects. The types of genetic variations used in these studies have changed in the past 25 years and can be classified into five major classes: RFLP (restriction fragment length polymorphism), VNTR (variable number of tandem repeat), STR (short tandem repeat), SNP (singlenucleotide polymorphism) and CNV (copy-number variation); furthermore, construction of the international SNP database and recent development of high-throughput SNP typing platforms enabled us to perform genome-wide association studies, which have identified genes or genetic variations susceptible to common diseases or those associated with drug responses. SNPs are found at a frequency of about 1:1000 bases in humans and they are changes in a single base at a specific position in the genome, in most cases with two alleles. By definition, the more rare allele should be more abundant than 1% in the general population; if the variant is rare, with a frequency below 0.1%, it is referred to as a mutation. More than 99% of these genetic variations are biologically silent, while some polymorphisms can affect biological function according to their position within the genome. Gene polymorphisms account for the polymodal distribution of the frequency of response to a drug in a non-homogeneous population, i.e. one encompassing multiple genetic profiles capable of affecting response. To leave the cell, some drugs are actively transported by membrane transporter proteins. The major transporter enzymes are MDR1 (multidrug resistance proteins), MRP (multidrug resistance-associated proteins) and OATP (organic anion-transporting polypeptides), where several genetic polymorphisms have been demonstrated. MDRs are transmembrane transporters of the large ABC protein family: P-glycoprotein (P-gp, or MDR1/ABCB1), the best known, is highly polymorphic. It can influence substrate absorption at the level of the blood brain barrier; high P-gp concentrations can limit entry of the required amount of drug, whereas low levels may result in abnormal accumulation. Recently, allele frequencies and findings regarding functional variants in drug transporter systems were reported in an interesting review. Variations in the sequence of the genes encoding the primary therapeutic target, such as receptors and ion channels, are capable of inducing protein forms with different functional characteristics. This can account for abnormal drug responses, which may also underpin some adverse reactions. numerous genetic, neurobiological, environmental factors that are still not yet fully understood. Numerous genes are upand/ or down-regulated by alcohol exposure: the ethanol-responsive genes mainly encode functional proteins such as proteins involved in nucleic acid binding, transcription factors, selected regulatory molecules, and receptors. Pharmacogenetic studies can be categorized into two methodologic approaches: genomewide linkage analysis and candidate gene approach. whether specific alleles of marker genes are found more often in individuals with the disease than in healthy subjects. The whole genome is analysed using markers that are uniformly distributed on all chromosomes, seeking chromosome regions that could contain genes involved in complex disorder susceptibility. The linkage is sought only in recent ancestors. Since only a small number of recombination events are involved, the gene regions detected by linkage analysis are likely to be large and to encompass hundreds or even thousands of genes. Genetic association studies assess correlations between genetic variants and trait differences on a population scale and they have been used widely to identify regions of the genome and candidate genes that contribute to complex disease. The common errors encountered in association studies of complex diseases are the small sample size, subgroup analysis and multiple testing, random error, poorly matched control group, failure to attempt study replication and to detect linkage disequilibrium with adjacent loci, overinterpreting results and positive publication bias, unwarranted candidate gene declaration after identifying association in arbitrary genetic region. Association studies draw from historic recombination so disease-associated regions are extremely small in outbred random mating populations, encompassing only one gene or gene fragment. As the disease mutation is transmitted from one generation to the next, recombination will separate it from the alleles of its original haplotype.

The definitions of genetic testing used by 65 organisations and entities, including genetics professional organisations, insurance organisations, pharmaceutical companies, and legal organisations, was reviewed; it was found that the definitions used were extremely variable; ranging from DNA testing solely, to any source that can provide unambiguous genetic information, including family history. Toxicogenetics can learn from the forensic sciences: the widely used technique of “genetic fingerprinting” uses a small number of highly polymorphic, unlinked genetic markers that have no known implications to the health of an individual. Advanced diagnostic analyses, genetic counselling, and interdisciplinary and multidisciplinary approach, involving neurobiological, genetical, toxicological, psychological, and social sciences, should be integral parts of forensic practice. A better understanding of genetic susceptibility to addiction may be also useful for ascertaining the causes and circumstances of death. Some gene variants may, in fact, determine in some individuals more sensitive to the substance, with an increased risk of toxic effects, even death.

Acknowledgements:

The Police Department;

www.politie.nl and a Chief Inspector – Mr. Erik Akerboom     ©

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