Pharmacogenetic screening of the gene deletion and duplications of CYP2D6

Cytochrome P450 (CYP) 2D6 is one of the most important enzymes involved in the metabolism of drugs. Multiple, clinically relevant, genetic variants of this gene have been identified and, among them, a gene deletion as well as multiplications of the gene. These large structural mutations in CYP2D6 occur at a relatively high frequency in several populations. Genotyping of CYP2D6 could therefore be applied to individualize drug therapy to improve therapeutic efficacy and decrease adverse effects in patients. However, a prerequisite for the pharmacogenetic screening of CYP2D6 in a clinical setting is the development of fast, reliable and cost-effective techniques for the routine genotyping of patients. In the case of CYP2D6, besides the general problems that arise in the detection of large gene deletions and multiplications, the presence of two highly homologous pseudogenes, CYP2D7 and CYP2D8, forms an extra challenge. This review provides an overview of the techniques that have been described to detect the CYP2D6 gene deletion and multiplication: Southern-blotting RFLP, long-template PCR, and real-time PCR. Of these techniques, real-time PCR is the only technique giving quantitative information about the exact copy number of the gene. Considering all of the other advantages of this method over other methods, such as cost-effectiveness and suitability for high throughput screening, real-time PCR is the most promising method for the genotyping of large structural alterations in the CYP2D6 gene in a routine clinical setting.     

Pharmacogenetic Screening of the Gene Deletion and Duplications of CYP2D6

Cytochrome P450 (CYP) 2D6 is one of the most important enzymes involved in the metabolism of drugs. Multiple, clinically relevant, genetic variants of this gene have been identified and, among them, a gene deletion as well as multiplications of the gene. These large structural mutations in CYP2D6 occur at a relatively high frequency in several populations. Genotyping of CYP2D6 could therefore be applied to individualize drug therapy to improve therapeutic efficacy and decrease adverse effects in patients. However, a prerequisite for the pharmacogenetic screening of CYP2D6 in a clinical setting is the development of fast, reliable and cost-effective techniques for the routine genotyping of patients. In the case of CYP2D6, besides the general problems that arise in the detection of large gene deletions and multiplications, the presence of two highly homologous pseudogenes, CYP2D7 and CYP2D8, forms an extra challenge.

This review provides an overview of the techniques that have been described to detect the CYP2D6 gene deletion and multiplication: Southern-blotting RFLP, long-template PCR, and real-time PCR. Of these techniques, real-time PCR is the only technique giving quantitative information about the exact copy number of the gene. Considering all of the other advantages of this method over other methods, such as cost-effectiveness and suitability for high throughput screening, real-time PCR is the most promising method for the genotyping of large structural alterations in the CYP2D6 gene in a routine clinical setting.     

Familial varieties of primary aldosteronism

1. Improved approaches to screening and diagnosis have revealed primary aldosteronism (PAL) to be much more common than previously thought, with most patients normokalaemic. The spectrum of this disorder has been further broadened by the study of familial varieties. 2. Familial hyperaldosteronism type I (FH-I) is a glucocorticoid-remediable form of PAL caused by the inheritance of an adrenocorticotrophic hormone (ACTH)- regulated, hybrid CYP11B1/CYP11B2 gene. Diagnosis has been greatly facilitated by the advent of genetic testing. The severity of hypertension varies widely in FH-I, even among members of the same family, and has demonstrated relationships with gender, degree of biochemical disturbance and hybrid gene crossover point position. Hormone "day curve" studies show that the hybrid gene dominates over wild-type CYP11B2 in terms of aldosterone regulation. This may be due, in part, to a defect in wild-type CYP11B2-induced aldosterone production. Control of hypertension in FH-I requires only partial suppression of ACTH and much smaller glucocorticoid doses than previously recommended. 3. Familial hyperaldosteronism type II (FH-II) is not glucocorticoid remediable and is not associated with the hybrid gene mutation. Familial hyperaldosteronism type II is clinically, biochemically and morphologically indistinguishable from apparently non-familial PAL. Linkage studies in one informative family did not show segregation of FH-II with the CYP11B2, AT1 or MEN1 genes, but a genome-wide search has revealed linkage with a locus in chromosome 7. As has already occurred in FH-I, elucidation of causative mutations is likely to facilitate earlier detection of PAL.     

Congenital adrenal hyperplasia: epidemiology, management and practical drug treatment

Congenital adrenal hyperplasia (CAH) owing to 21-hydroxylase deficiency is a common disorder, and is characterised by a defect in cortisol biosynthesis with or without a defect in aldosterone synthesis and androgen excess. The classic form, also known as the severe form, occurs in 1:15,000 births worldwide, while the nonclassic or mild form occurs in approximately 1:1,000 births worldwide and is much more common (up to 1:20) in certain ethnic groups. In classic 21-hydroxylase deficiency, glucocorticoids are given in doses sufficient to suppress adrenal androgen secretion, and mineralocorticoids are given to normalise electrolytes and plasma renin activity. The management of CAH may be complicated by iatrogenic Cushing's syndrome, inadequately treated hyperandrogenism, or both. Prenatal treatment may decrease virilisation of the affected female foetus, but the efficacy and safety of treating CAH prenatally remains to be fully defined. Close clinical monitoring of growth and development is essential to optimise treatment outcome. New treatment approaches are currently under investigation in the most severely affected patients, while nonclassic CAH does not always require treatment.     

新生儿先天性肾上腺皮质增生症筛查中17羟孕酮切值的建立

目的回顾性分析2010年1月-2010年9月,我院新生儿先天性肾上腺皮质增生症（CAH）的筛查数据,初步探讨不同性别、出生孕周及体重的新生儿17-羟孕酮（17-OHP）分布情况,并结合临床确诊病例,设定合理的筛查切值。方法采用时间分辨荧光免疫分析方法检测新生儿末稍血17-OHP浓度,采用百分位数法确定切值。结果新生儿筛查的17-OHP检测水平呈偏态分布;不同性别、体重及孕周的17-OHP亦有显著性差异;根据稳健回归统计发现孕周与170HP的相关性最好,所以在设定切值时分设早产儿和足月儿即可。早产新生儿（〈37周117-OHP的99％百分位数值为66．1nmol／L;正常孕周（≥37周）新生儿17-OHP的99％百分位数值为26．6nmol／L,与早产新生儿组差异有显著性（P〈0．01）。本文跟踪统计了从2010年1月到2011年8月间筛查的88061例活产新生儿,一共确诊了17例CAH,其中失盐型2例,发病率为1／44030;单纯男化型1例,发病率为1／88061;非典型14例,发病率为1／6290。结论中山地区的CAH发病率明显低于全国水平。用统一的17-OHP切值30nmol／L对新生儿CAH筛查结果有一定影响,建议早产儿筛查切值为60nmol／L,以减少假阳性率和召回率。     

新生儿疾病筛查人群中CYP21基因P30L和V281L突变携带者频率的研究

目的研究新生儿疾病筛查人群中CYP21基因P30L和V281L突变杂合子的频率分布。方法58份新生儿干血滤纸片测定17-OHP,同时提取新生儿脐带血DNA,应用PCR扩增和限制性内切酶分析P30L和V281L两种与21-OHD相关的CYP21基因突变,计算杂合子频率。结果在116个等位基因中有1个鉴定出P30L突变,未鉴定出V281L突变。本研究人群中P30L的携带者频率为0.9%,V281L的携带者频率为0。结论本研究新生儿筛查正常人群中可检出CYP21基因突变携带者,对人群中CYP21基因突变携带者的研究有助于对漏检21-OHD的基因突变分析。     

Genetic Polymorphism of Drug Metabolizing Enzymes: New Mutations in CYP2D6 and CYP2A6 Genes in Japanese

Genetic polymorphism of drug metabolizing enzymes, particularly cytochrome P450 (CYP), is an important cause of adverse drug reactions. Multiple gene mutations in CYP have been shown to be phenotype. The occurrence of genetic polymorphism has been seen in genes for CYP1A1, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A5. This review discusses the molecular mechanism of two genetic polymorphisms, debrisoquine/sparteine (CYP2D6) coumarin (CYP2A6) polymorphisms. In addition, elucidation of gene mutations of CYP2D6 and CYP2A6 in Japanese will be discussed.     

细胞色素P450氧化酶基因多态性对药物代谢影响的研究进展

细胞色素P450氧化酶是人体内的一种重要代谢酶,它能代谢和/或活化许多种药物、前致癌物、前毒物和致变剂。细胞色素P450氧化酶的基因具有遗传多态性,在人类存在等位基因的突变体。本文从基因结构、底物和影响其活性的因素、遗传多态性的分子机制等方面综述细胞色素P450氧化酶的研究进展。     

Molecular study of FMF patients in Armenia

Familial Mediterranean Fever (FMF, MIM 249100), or Periodic disease, is a recessively transmitted and ethnically restricted condition prevalent in population from the Mediterranean decent. FMF notoriously has been hard to diagnose until mutations in the MEFV gene have been identified and as a tremendous help are used for the diagnosis of difficult cases. Since FMF can be controlled by medication, it is extremely desirable to have a firm diagnosis. The aim of this study was to establish the frequency of the most common mutations and genotypes in Armenian population. Molecular analysis of MEFV gene mutations in 3000 Armenian patients has demonstrated direct correlation between the clinical severity and the molecular diagnostic criteria of the disease, including the development of renal amyloidosis with MEFV genotypes. MEFV genotyping performed in the framework of a genetic counseling may reveal and identify affected individuals in presymptomatic phase, providing the possibility of a precocious start of the therapy.     

The CYP2C19 enzyme polymorphism

The genetic test is gradually replacing probe drugs as the primary tool for screening populations for the CYP2C19 polymorphism. A full appreciation for the clinical and toxicological relevance of this genetic variation is presently limited. Further research is needed in several areas. The development and use of 3-D models of the CYP2C19 enzyme to automate and increase the rate at which CYP2C19 substrates are identified could reap great benefits. Meanwhile, clinical research should begin to determine whether the CYP2C19 polymorphism affects therapeutic outcomes and toxicity of drugs in actual patient settings. Combining research efforts in molecular modeling, genetic testing, clinical and epidemiological research will be required if better appreciation of this genetic variation and its importance in the population at large is to emerge.     

Genetic polymorphisms of the drug-metabolizing enzyme cytochrome P450 3A5 in a Uyghur Chinese population

1. Detection of CYP3A5 variant alleles, and knowledge about their allelic frequency in Uyghur ethnic groups, is important to establish the clinical relevance of screening for these polymorphisms to optimize pharmacotherapy.

2.?We used DNA sequencing to investigate the promoter, exons and surrounding introns, and 3′-untranslated region of the CYP3A5 gene in 96 unrelated healthy Uyghur individuals. We also used SIFT and PolyPhen-2 to predict the protein function of the novel non-synonymous mutation in CYP3A5 coding regions.

3.?We found 24 different CYP3A5 polymorphisms in the Uyghur population, three of which were novel: the synonymous mutation 43C?>?T in exon 1, two mutations 32120C?>?G and 32245T?>?C in 3′-untranslated region, and we detected the allele frequencies of CYP3A5*1 and *3 as 64.58% and 35.42%, respectively. While no subjects with CYP3A5*6 were identified. Other identified genotypes included the heterozygous genotype 1A/3A (59.38%) and 1A/3E (11.46%), which lead to decreased enzyme activity. In addition, the frequency of haplotype “TTAGGT” was the most prevalent with 0.781.

4.?Our data provide new information regarding CYP3A5 genetic polymorphisms in Uyghur individuals, which may help to improve individualization of drug therapy and offer a preliminary basis for more rational use of drugs.     

细胞色素氧化酶CYP2C9的研究进展

CYP2C9是人类肝脏中含量丰富的一种CYP450酶,它能代谢和／或活化许多种药物、前致癌物、前毒物和致突变剂。CYP2C9基因具有遗传多态性,在人类存在几种等位基因的突变体。本文从基因结构、底物和探针药、影响其活性的因素、遗传多态性的分子机制等方面综述CYP2C9的研究进展。     

Clinical pharmacogenetics and potential application in personalized medicine

The current 'fixed-dosage strategy' approach to medicine, means there is much inter-individual variation in drug response. Pharmacogenetics is the study of how inter-individual variations in the DNA sequence of specific genes affect drug responses. This article will highlight current pharmacogenetic knowledge on important drug metabolizing enzymes, drug transporters and drug targets to understand interindividual variability in drug clearance and responses in clinical practice and potential use in personalized medicine. Polymorphisms in the cytochrome P450 (CYP) family may have had the most impact on the fate of pharmaceutical drugs. CYP2D6, CYP2C19 and CYP2C9 gene polymorphisms and gene duplications account for the most frequent variations in phase I metabolism of drugs since nearly 80% of drugs in use today are metabolised by these enzymes. Approximately 5% of Europeans and 1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant drug metabolising enzyme that demonstrates genetic variants. Studies into CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and CYP2C9*3 alleles. Extensive polymorphism also occurs in a majority of Phase II drug metabolizing enzymes. One of the most important polymorphisms is thiopurine S-methyl transferases (TPMT) that catalyzes the S-methylation of thiopurine drugs. With respect to drug transport polymorphism, the most extensively studied drug transporter is P-glycoprotein (P-gp/MDR1), but the current data on the clinical impact is limited. Polymorphisms in drug transporters may change drug's distribution, excretion and response. Recent advances in molecular research have revealed many of the genes that encode drug targets demonstrate genetic polymorphism. These variations, in many cases, have altered the targets sensitivity to the specific drug molecule and thus have a profound effect on drug efficacy and toxicity. For example, the beta (2)-adrenoreceptor, which is encoded by the ADRB2 gene, illustrates a clinically significant genetic variation in drug targets. The variable number tandem repeat polymorphisms in serotonin transporter (SERT/SLC6A4) gene are associated with response to antidepressants. The distribution of the common variant alleles of genes that encode drug metabolizing enzymes, drug transporters and drug targets has been found to vary among different populations. The promise of pharmacogenetics lies in its potential to identify the right drug at the right dose for the right individual. Drugs with a narrow therapeutic index are thought to benefit more from pharmacogenetic studies. For example, warfarin serves as a good practical example of how pharmacogenetics can be utilized prior to commencement of therapy in order to achieve maximum efficacy and minimum toxicity. As such, pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and licensed drugs.     

21羟化酶缺乏症高风险胎儿的产前诊断分析

目的 对1例21羟化酶缺乏症（21OHD）先证者家系CYP21A2基因缺陷高风险胎儿进行产前分子诊断.方法 提取先证者及其父母的外周血DNA,分段扩增CYP21A2基因全长并测序,确定先证者及父母基因型.采用亲子鉴定试验排除母体DNA污染.针对先证者突变位点,扩增羊水DNA并测序.结果 测序结果显示先证者存在IVS2-13A〉G纯合突变,父母均为携带者.比较STR位点未见羊水DNA受母体DNA污染迹象.胎儿为该突变杂合子,判断胎儿为携带者.培养后羊水检测结果与培养前一致.胎儿娩出后发育良好,证实了产前诊断结果.结论 建立了21OHD产前分子诊断方法,并成功应用于1例21OHD高风险胎儿的产前诊断分析.     

厦门地区2960对育龄夫妇地中海贫血筛查及基因检测结果分析

目的 初步了解并分析厦门地区育龄青年地中海贫血(地贫)流行情况及其基因分布特征,为地贫基因诊断、遗传咨询及减少地贫漏诊和误诊提供理论依据.方法 对2013年4月至2016年4月来本院进行孕前优生健康检查的2 960对育龄夫妇进行血常规、血红蛋白电泳、血清铁、铁蛋白筛查,筛查阳性患者通过“PCR+膜杂交法”进行地贫基因检测.结果 2 960对育龄夫妇经血液学筛查结果中阳性共1 160例(占19.59％),检出地贫基因携带者408例,占6.89％;其中α地贫基因携带者286例,占4.83％,最常见的地贫基因型为--SEA/αα,占全部α地贫基因携带者的74.13％;β地贫基因携带者1 14例,占1.93％,最常见的地贫基因型为CD41-42(-TCTT)和IVS-2-654(C→T),分别占全部β地贫基因携带者的34.21％和32.46％;α地贫复合β地贫基因携带者8例,占0.14％.结论 厦门地区地贫基因突变类型复杂多样,α地贫基因携带者最常见的基因型为--SEA/α α,β地贫基因携带者最常见的基因型为CD41-42(-TCTT)和IVS-2-654(C→T);对于血液学筛查阳性的人群,进一步进行地贫基因诊断,可避免漏诊误诊,更好的为临床地贫诊断和遗传咨询提供依据.     

Pharmacogenetics in transplant patients: can it predict pharmacokinetics and pharmacodynamics?

Pharmacogenetics holds the potential to allow individualized dosing of immunosuppressive agents to optimize their therapeutic effect while minimizing adverse effects. As more pharmacogenetic information accumulates, the prospect of reducing or discontinuing the intensive therapeutic drug monitoring of immunosuppressants looks attractive. However, the long process of developing useful clinical information from basic information on the genes of interest is at a very early stage, and our present information does not supercede pharmacokinetic or blood concentration monitoring of immunosuppressants. The most extensive blood concentration/dose information available is on tacrolimus and its dosing related to CYP3A5 and ABCB1 gene polymorphisms. Although CYP3A5 genotype is definitely associated with tacrolimus dosing, the only recommendation presently published is for an arbitrary doubling of the starting tacrolimus dose in CYP3A5 expressors. For cyclosporine, sirolimus, and corticosteroids, the presently available pharmacogenetic information does not permit pharmacokinetic predictions. The pharmacodynamics of immunosuppressants, as evidenced by effects on acute rejection or adverse drug effects, have considerably more potential for prediction by pharmacogenetic models. Drug-resistant rejection, nephrotoxicity, steroid resistance and osteonecrosis, and even patient survival may ultimately be predicted by models incorporating multiple gene polymorphisms and other critical patient information. At this point, treatment algorithms can be developed that will allow us to individualize a transplant patient's immunosuppressive therapy.