GENETIC FACTORS IN DRUG THERAPYClinical and molecular pharmacogenetics

David A. Price Evans, MD, DSc, PhD, FRCPDirector of Medicine, Riyadh Armed Forces Hospital, Saudi Arabia

CAMBRIDGEUNIVERSITY PRESS

CONTENTS

Preface page xxiii

^Part I Introduction1 The arrangement of the information in this volume 12 General introduction 2

Adverse reactions 2Lack of efficacy 2Variation: the raw material of genetics 3Historical perspective 3

3 Classification of pharmacogenetic phenomena 6Introduction 6Discovery of single gene effects 6The concept of polymorphism 7Polygenic effects 7Inter-ethnic variability 8

Part II Cytochrome P450 based phenomena4 Cytochromes P450 - general features 9

Introduction 9Molecular structure 10A protein in evolution 10Function 11Categories in human cytochromes P450 13Inducibility 16Chromosomal localization 17

5 Arylhydrocarbon hydroxylase (cytochrome P450 1A1 and 1A2) 19Introduction 19The Ah locus in the mouse 19

A non-invasive test 19The responsible cytochromes P450 20The Ah receptor 20The relationship of the Ah gene to the cyp lal gene 20The effects of Ah responsiveness in mice 21

Studies of arylhydrocarbon hydroxylase in humans 21

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CONTENTS

Human lymphocyte preparations 21Human peripheral blood monocytes 22Bronchogenic carcinoma 23Leukaemia and solid tumours 27Smoking appears to protect against aflatoxin hepatoma 27Earlier menopause in smoking women 27Arylhydrocarbon hydroxylase activity and drug metabolism 27The molecular genetics of cytochromes P4 50 1A1 and 1A2 in man 30

Conclusions 31The mephenytoin hydroxylation polymorphism (cytochrome P450 2C18) 35

The discovery of the polymorphism 35Genetic nature of the polymorphism 36Comparisons of various populations 37Metabolic differences between phenotypes 40Enzymic basis of the polymorphism 42Chemical inhibition studies 42Studies on molecular structure and gene localization 44Other drugs metabolized polymorphically by the mephenytoin

polymorphism 45Drugs which are not influenced by the mephenytoin polymorphism 48Induction 48Phenotyping procedures 48Direct clinical effects 49Association of phenotypes with spontaneous disorders 49Similar polymorphism in non-human primate 50

The debrisoquine/sparteine polymorphism (cytochrome P450 2D6) 54The metabolism of debrisoquine and the definition of phenotypes 54The sparteine polymorphism 55Family studies of debrisoquine metabolism 56Family studies of other drugs 57Drugs whose metabolism is controlled by the alleles controlling the

debrisoquine and sparteine hydroxylation polymorphism 57Phenotyping tests 59Drugs whose metabolism is not controlled by the debrisoquine/sparteine

polymorphism 61Interactions in vivo between drugs known to be substrates for

debrisoquine/sparteine polymorphic oxidation 61Other interactions 62The effects of inducer and inhibitor compounds in vivo on drug

metabolism mediated by the debrisoquine/sparteine polymorphism 64Enzymological studies 64In vitro inhibition studies of the cytochrome P450 responsible for the

debrisoquine/sparteine polymorphism 65Molecular genetics 69Chromosomal localization 73Inter-ethnic variability 74Clinical consequences 78Associations between debrisoquine/sparteine phenotypes and spontaneous

disorders 82Conclusion 88

CONTENTS

8 The cytochrome P450 3A subfamily 102Introduction 102Nifedipine 102

The frequency distributions of pharmacokinetic parameters 102Additional information 103Biochemical aspects 105Molecular genetics 105Gene mapping 105Inducibility of cytochrome P450 3A4 106Likely substrates for cytochrome P450 3A4 as suggested by

immuno-inhibition studies 106Inter-subject variability 106Inter-ethnic variability 107

Cyclosporine 107Lidocaine 109Tamoxifen 109Conclusion 110

9 Tolbutamide 113Introduction, and a genetic hypothesis 113In vivo assessments of interactions of other drugs with tolbutamide

metabolism 114In vitro observations using human liver preparations 114Molecular genetics 116

10 Phenytoin 119Introduction , 119Interaction between diphenylhydantoin and the polymorphic

acetylation of isoniazid 120Genetic control of phenytoin metabolism 121Correlation of diphenylhydantoin hydroxylation with the

hydroxylation of other compounds 123Poor parahydroxylation of phenytoin and Parkinson's disease 126Idiosyncratic adverse reactions and epoxide hydrolases 126Inter-ethnic variability in phenytoin metabolism 130

11 Some other drugs of special interest 132Warfarin 132Metronidazole 132Phenacetin 133

12 Cytochrome P450 reductase 13413 General conclusions 135

Part III Cholinesterase14 Cholinesterase 137

Introduction 137Mechanism of action of succinylcholine 137Assessment of the degree of neuromuscular block 137Early discoveries - multiple alleles 138New alleles 141Heterogeneity of the 'silent' phenotype 142The succinylcholine apnoea-prone person of 'normal' phenotype 143

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Electrophoretically determined polymorphisms 144High activity cholinesterase variants 146Genetic linkage and chromosomal localization 146Techniques for assessing cholinesterase activity and phenotypes

including the use of automated methods 147Molecular biology of cholinesterase 147Miscellaneous clinical topics 152The use of succinyldicholine as an in vitro test substance for

cholinesterase assessment 154Cholinesterase enzyme treatment to prevent apnoea caused by

succinylcholine 155The relationship between cholinesterase and plasma lipoproteins 155Inter-ethnic variability in the frequencies of the alleles controlling

cholinesterase variants 156Appendix 157

Part IV Alcohol and alcoholism15 Alcohol and alcoholism 177

The objectives of this chapter 177Historical background 177A pharmacogenetic approach 177Definitions 178Alcohol-related problems are influenced by heredity and environment 178

Familial studies 179Twin studies 179

The attributes of persons genetically susceptible to alcoholism:'at risk' individuals 180

The psychological attributes of 'at risk' individuals 180Physiological markers 181Alcohol and the electroencephalogram 181Biochemical markers 182Genetic control of a brain mechanism which responds to alcohol -

a first attempt 183Genetic control of the metabolism and effects of alcohol 183

Twin studies of the metabolism of alcohol 183Inter-ethnic variability in the effects of alcohol 183Inter-ethnic comparisons of the rates of alcohol metabolism 185

Alcohol dehydrogenase 186The metabolism of alcohol in man 186A variant form of alcohol dehydrogenase 186A complex genetic polymorphism 186Molecular genetics of ADH 189Chromosomal localization 189Gene organization 189Restriction fragment length polymorphisms 190ADH genotyping using DNA from leucocytes 190Application and speculation 191

Aldehyde dehydrogenase 192Different types of acetaldehyde dehydrogenase 192Cytosolic and mitochondrial liver aldehyde dehydrogenase 194

CONTENTS X I I I

A technical advance in studying the acetaldehyde dehydrogenasephenotype 194

Ethnic distribution 194Molecular genetics 195Chromosomal localization 196The pharmacological effects of alcohol in relation to aldehyde

dehydrogenase type 196Alcohol consumption in relation to the Japanese ALDH2

polymorphism 198An association of an acetaldehyde dehydrogenase phenotype with

alcoholism 198Some further considerations concerning ALDH deficiency 199

Two new associations of phenotypes within polymorphisms withalcoholism 200

Genetic predisposition to the sequelae of alcoholism 200The effects of alcohol on chromosomes and chromatids 202The fetal alcohol syndrome 202A resume and a perspective 203

Part V N-Acetyltransferase16 JV-Acetyltransf erase 211

Summary 211Introduction and initial discovery of the polymorphism 211

Genetic Investigations 212Drugs other than isoniazid which are polymorphically acetylated 214Techniques for determining the acetylator phenotype 215

Isoniazid tests 218Sulphamethazine tests 218Sulphapyridine 220Other phenotyping methods 222The search for a genotyping test 222

Factors influencing acetylator phenotyping tests 222The effect of age on the ]V-acetylation process and its polymorphism 226Height and weight 227

The metabolic basis of the polymorphism 227Further studies on the molecular nature of the enzyme polymorphism 228

Molecular biology 230Associations of clinical responses to drugs with acetylator phenotypes 232

Isoniazid 232Hydralazine 241Dihydralazine and endralazine 244Sulphapyridine - a metabolite of salicylazosulphapyridine 244Nitrazepam 247Aminoglutethimide 247Procainamide 249Dapsone 250Caffeine 251Phenelzine 253Miscellaneous observations 254

When should one do an acetylator phenotyping test in clinical practice? 255

XIV CONTENTS

The global distribution of allele frequency 255Associations between acetylator phenotypes and spontaneous disorders 258

Bladder cancer 261Occupational exposure to polymorphically acetylated compounds 266Colorectal carcinoma 267Carcinoma of the larynx 269Bronchial carcinoma 269Cancer of the breast 269Lymphoma 269Rheumatoid arthritis 273Systemic lupus erythematosus 273Diabetes 276Miscellaneous disorders 277Discussion 285

Conclusions 285

Part VI Miscellaneous Phase II reactions showing genetic variability in drug metabolism17 The glucosidation of amobarbital 303

Introduction 303A new approach 303Inter-ethnic studies 304The possibility of in in vitro studies of glucosidation 304Stereoisomer formation 304Glucose conjugation of other drugs 305Epilogue 305

18 Glucuronosyltrarisf erases 306Introduction 306Relationship of drug glucuronidation to spontaneously occurring

genetic disorders 307Similarities to the cytochrome P450 system 310Recent advances in the molecular biology of UDP glucuronosyl-

transf erase enzymes 311The search for genetic polymorphisms of drug glucuronidation in man 313Differential induction of drug glucuronidation 314Possible future developments 314

19 Glutathione-S-transf erase 317Introduction 317Different classes of glutathione-S-transferases 318Genetic polymorphisms 319Gene structure 321Gene localization 322Tissue distribution 322Induction and inhibition 323Inter-ethnic distribution 323The glutathione-S-transferase mu polymorphism and spontaneous

disorders 323Glutathione-S-transferases and drug effects 325Relevance of GST to occupational medicine 326

20 Methylation reactions 330Introduction 330

CONTENTS XV

Thiopurine methyltransferase 330Assay and genetics 330Inter-ethnic variability 332TPMT in other cells and tissues 332In vitro substrates and inhibitors 333Clinical applications 333

Thiol methyltransferase 336Introduction 336Genetics 336Drugs metabolized 337Relation to spontaneous disease 337

Catechol-O-methyltransf erase 338Genetics 338Linkage and gene localization 339Identity of genetic control in erythrocytes and internal organs 339Clinical applications 340

HistamineJV-methyltransf erase 341Phenol methyltransferase 342Conclusions 342

21 Paraoxonase 346Introduction 346Genetic studies 346Advances in phenotyping and genotyping techniques 348Inter - ethnic variability 349Further genetic analyses 356Linkage of the paraoxonase locus with the cystic fibrosis locus 356Enzymology 357Relationship of paraoxonase to myocardial infarction and association

with HDL cholesterol 358Molecular genetics 360

22 Sulphotransferases 364Introduction 364Correlation of the phenol sulphotransferase activity of platelets with that

of other cells and tissues 365Genetic studies 365Thermostable (P-form) human phenol sulphotransferase cloned 366Inter-ethnic comparisons 367Correlations of variability in platelet PST with drug metabolism 367Relationship to a spontaneous disorder 368JV-sulphotransferase 369

23 Sulphoxidation deficiency 371Introduction 371Genetic aspects 372Relationship to established polymorphisms . 374Site of sulphoxidation 374A curiosity - black speckled dolls 374Clinical studies 374The story takes a new turn 377Other drugs which are sulphoxidized 377

24 Halothane hepatitis and other topics 382

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Halothane hepatitis 382Methoxyflurane 383Carbamazepinehypersensitivity 383Oral contraceptive steroids 384Anti-cancer drugs 386Trimethylamine 387Odoriferous urine after asparagus ingestion 388

Part VII Glucose-6-phosphate dehydrogenase deficiency25 Glucose-6-phosphate dehydrogenase deficiency 391

Introduction 391Haemolytic anaemia after primaquine ingestion 391Cross-transfusion experiments 391Enzymic basis 392Genetic studies 393Variant forms of G6PD 393Analysis of the protein structure 395Molecular genetics 395An evolutionary perspective 398Genetic linkage 399Gene localization 399G6PD in cells and tissues other than erythrocytes 399X-inactivation in the female 399The clinical effects of G6PD variants 401

Malaria 401Favism . 403Neonatal jaundice 405Hereditary non-spherocytic haemolytic anaemia 406Chemicals causing haemolysis in G6PD deficient subjects 407Bacterial and viral infections 409

Methods of detecting G6PD deficiency 409Miscellaneous observations 409

(a) Glucose tolerance 409(b) Hypertension, pulse rate and serum creatinine 410(c) Cancer 410(d) Clonal origin of tumours 411(e) Oestrogen receptors in breast cancer 411(f) Thyrotoxicosis and erythrocytic G6PD activity 412(g) Interactions between G6PD deficiency and sickle haemoglobin 412(h) Cataracts 413(i) Apparent severe deficiency of leucocyte glucose-6-phosphate

dehydrogenase 413Serum lipids 414Predictions of haemolysis in vivo from laboratory data 415Conclusion 415

Part VIII The hepatic porphyrias26 The hepatic porphyrias 423

Introduction 423Haem synthesis 423Classification of porphyria disorders 425The acute porphyrias 428

CONTENTS XVII

The mechanism of production of the acute porphyrias 428The therapy of the acute porphyrias 430

Porphobilinogen synthase deficiency 433Enzyme polymorphisms 433A type of acute pophyria 433Molecular biology 434Lead toxicity 435

Acute intermittent porphyria 435Clinical features 435Diagnosis and biochemical investigations 436Identification of the enzymic defect 436Molecular genetics 438Homozygous AIP 439

Hereditary coproporphyria 439Porphyria variegata 443

Clinical features 443Biochemical abnormalities 443Genetics 445Homozygous porphyria variegata 445

Porphyria cutanea tarda 445Metabolic abnormalities 446Enzymological and genetic studies 446Hepato-erythropoietic porphyria 447Enzyme-environment interaction 448Molecular genetics , 448Management 449

Dual porphyria and Chester porphyria 449Pseudoporphyria 451

Conclusions 452

Part DC Malignant hyperthermia27 Malignant hyperthermia 459

Clinical description 459Incidence 460Ethnic distribution 460Preventing MH 460When MH occurs 460The MH phenotype - a possible occupational hazard 461Tests which identify the MH-susceptible phenotype 462

The muscle contracture test 462Drugs and the in vitro muscle contracture test 465Creatine phosphokinase 466Prediction of MH susceptibility by means of clinical signs 466Muscle abnormalities to be found in the MHS phenotype 466Other predictive tests 467

Counselling and information 467Reactions of the MH type occurring in other disorders 468

Central core disease 468Duchenne muscular dystrophy 468The King-Denborough syndrome 468

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Myoadenylate deaminase deficiency 469Myotonia 469Other conditions 469

Possible associations between MH and other conditions 469Sudden infant death syndrome (cot death) 469Neuroleptic malignant syndrome 470

Aberrant physiology 470Normal muscle contraction 470The MH muscle 473Malignant hyperthermia in pigs 474

Genetic aspects 474Linkage 476

A single point mutation 477Appendixes 480

Part X Miscellaneous systems showing genetic variability in response to drugs28 Chlorpropamide-alcohol flushing 489

Introduction 489Differentiation from flushing on ethanol alone 489Inheritance 489Associations with diabetes 489Associations with the complications of diabetes 492Association with acetylator phenotype 492The possibility of an in vitro test 492Circulating metenkephalin in CPAF 492Prostaglandin synthetase inhibitors 493The phenotyping test 493Conclusion 497

29 Glucocorticosteroids and intraocular pressure 499An adverse reaction 499Population surveys 499Family studies 500Further genetic studies — conflicting evidence 501The contribution of the P" and PL alleles to the control of the basal

pressure of the healthy eye 501Predisposition to primary glaucoma detected by ocular corticosteroid test? 504Secondary glaucoma 505Two tests influenced by allelic genes PL and P" 505

(a) Glucose tolerance 505(b) The plasma cortisol suppression test 505

Conclusion 50530 Unstable haemoglobins 507

Clinical observations 507Laboratory investigations 507Genetic studies 508

The properties of haemoglobin Zurich 508A second haemoglobin Zurich family 509Phenazopyridine and carbon monoxide 509

The molecular basis of the interaction of sulphonamides withhaemoglobin Zurich 509

CONTENTS XIX

Other unstable haemoglobins affected by sulphonamides 510Conclusions 510

31 Human lymphocyte antigens and adverse reactions to drugs 512Introduction 512Reactions to the treatment of rheumatoid arthritis 512Systemic lupus erythematosus-like syndrome (pseudolupus) 515Mechanism 516

32 The polymorphism for tasting phenylthiocarbamide (PTC synphenylthiourea) 518

Prologue 518Discovery 518The technique of detecting the PTC taste polymorphism 518Genetics 522Linkage 525Factors influencing the PTC taste-titre 525The mechanism which is responsible for the taste-testing polymorphism 526The physico-chemical investigation of taste thresholds 527Effect of thyroxine precursors on taste-testing 527Neurological considerations 527Substances other than PTC which detect the tasting polymorphism 528Another similar taste-testing polymorphism 533Inter-ethnic variability 534Associations of PTC phenotypes with spontaneous disorders 534

Thyroid disorders 534Food dislikes and preferences 539Other conditions 541

Epilogue 54333 Hereditary anticoagulant resistance 547

Clinical experience 547Vitamin K 549Hereditary warfarin resistance in rats 549Relevance of the work in rats to human hereditary warfarin resistance 551Variation in the response to oral anticoagulants in non-extraordinary

subjects 55234 NADH-cytochrome b5 reductase 555

The nature of methaemoglobin 555The formation of methaemoglobin 555Physiologic mechanisms for reduction of methaemoglobin 555Origin and development of erythrocytic NADH-cytochrome b5 reductase 556Genetic variation of NADH-cytochrome b5 reductase 557Different clinical types of congenital methaemoglobinaemia 558Structures and molecular genetics of NADH-cytochrome b5 reductase

and cytochrome b5 559Chromosomal localization 559Acquired methaemoglobinaemia 559Gene frequency of NADH-cytochrome b5 deficiency in Caucasians 561Methaemoglobinaemia due to haemoglobin variants 562Diagnosis 562Treatment 562

35 Catalase 568

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A clinical observation 568Oral gangrene (Takahara's disease) 568Catalase in cells and tissues other than erythrocytes 569Genetics of acatalasia 569Chromosomal localization of the catalase gene 570Molecular genetics 570Structure of catalase 571Function of catalase 571Genetic variants of acatalasia 571Ethnic distribution of acatalasia 572A speculation 572

36 Antibiotic-induced deafness, chloramphenicol toxicity and other topics 574Antibiotic-induced deafness 574Fluorouracil and familial pyridinaemia 574Chloramphenicol-induced marrow depression 577Nail pigmentation following cancer chemotherapy 577Hereditary predisposition in drug-induced Parkinsonism 578Minocyclinic-induced potassium loss from erythrocytes 578Tumour resistance to multiple chemotherapeutic agents 578Lithium 579Black thyroid associated with minocy dine therapy 580A green man after indomethacin 580Drug binding to plasma proteins 580Chloroquine-inducedpruritis 581

Part XI Polygenic effects in pharmacogenetics37 Polygenic effects in pharmacogenetics 585

Introduction 585Nortriptyline 586Phenylbutazone 586Dicumarol 588Antipyrine 588Theophylline 589Conclusion 590

Part XII Common themes38 Common themes 593

Introduction 593Occupational medicine 593Toxicological implications 595Cancer 596Inter-ethnic variability 598

Single gene (major gene) phenomena 598Quantitative, multifactorial or polygenic systems 600

A public health perspective 600Molecular modelling 605Implications of pharmacogenetic polymorphisms for drug development

and regulation 607Pharmacogenetic approaches to the study of the aetiology of common

disorders 609

CONTENTS

Part x m Conclusions39 Conclusions

Part XIV Appendixes

XXI

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Appendix I Computing the degree of dominance 619Appendix II Exponential decay 621Appendix HI The disentanglement of overlapping frequency distribution curves 622Appendix IV Chromosomal locations of genes 625Appendix V General bibliography 627

Index 629