- Email: [email protected]
Pharmacogenetics in cerebrovascular disease
Seminars in Cerebrovascular Diseases and Stroke Vol. 3 No. 1 2003
Pharmacogenetics in Cerebrovascular Disease KATRINA GWINN-HARDY Bethesda, Maryland
ABSTRACT The principles of pharmacogenetics are a longstanding component of clinical practice, in which the physician chooses therapy based on the profile of the patient's historic and diagnostic features, to maximize benefit and minimize adverse events. However, the tools of modern molecular biology have allowed increased sophistication to be applied to the profiling of patients to optimize treatment. While these tools are not yet available to the practicing clinician, an awareness of the concepts on which they are based is of interest, as they are likely to become available and 'widely used in the future. Keywords: pharmacogenetics, genetics, stroke, risk factors.
Although pharmacogenetics is the subject of considerable hype, the concepts underlying it are not new. For example, when a clinician considers treatment based on ethnicity or gender, family histo12r and/or allergies (all of which are influenced by genetic factors), he or she is using pharmacogenetic principles. Glucose-6-phosphate dehydrogenase (G6PD) deficiency, which can lead to adverse drug reactions, has long been known to be more common in African and Mediterranean people than in those of northern European origin.1 Malignant hyperthermia, 2 long QT syndrome 3 venous thromobembolic disease, 4 and tardive dyskinesia 5 among many other examples, have all been associated with underlying genetic risk factors. New tools such as DNA microarray technology, 6 high-output screening systems, and advanced bioinformatics, when combined with the infrastructures of large simple clinical trials, will lead to a better understanding of pharmacogenetics. Genetic causes of disease range from classic Mendelian (a single gene leads to disease) to complex (multiple genes contribute to risk for disease in combination with other genetic and/or environmental factors). While rare, single gene disorders are important, in part because they
elucidate pathways leading to disease. 7 Pharmacogenetic studies, however, are based on common genes of lesser influence. One method of identifying genetic risk factors is the candidate gene association study, in which a given polymorphism in a gene of interest is compared between cases or controls; if the polymorphism is more common in affected subjects, a contribution to risk for disease is implied. A candidate gene is usually selected because the gene product is intuitively related to the disease process.
Stroke Genetics and Pha rmacogenetics Many genetic influences on stroke and its risk factors have been established. 8 Single gene disorders that cause stroke include hemoglobinopathies, dyslipoproteinemias, and cardioembolic disorders. 9,1~ Family history of ischemic stroke is a major risk factor for the disease.9,11 Ethnicity is also a risk factor; age-standardized mortality rates for stroke is higher among African Americans than Whites.12 Family history is an independent risk factor for subarachnoid hemorrhage (SAH). 13 Most clinicians separate stroke into ischemic and hemorrhagic types as two broad categories (and those into subcategories), and one might surmise that such stratification would be important for gene discovery. The experience in stroke suggests the opposite; grouping all types of stroke together has been successful. A genome scan of 476 patients (from 179 extended Icelandic pedigrees) considered all types of -
From the National Institute of Neurological Disorders and Stroke, Bethesda, MD.
Address reprint requests to Katrina Gwinn-Hardy, MD, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892. E-mail: gwinnk @ninds.nih.gov. 9 2003 Elsevier Inc. All rights reserved.
1528-9931/03/0301-0008530.00/0 doi: 10.1053/scds.2003.00014
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Seminars in Cerebrovascular Diseases and Stroke Vol. 3 No. 1 March 2003
stroke together, and revealed linkage to a 20 centiMorgan (cM) region on 5q12 where a gene for stroke is likely to lie. TM Genes related to the coagulation system are logical candidates for genetic susceptibility studies. Factor V Leiden and prothrombin (Factor II) mutations are putative risk factors for stroke. 15-19The higher risk for thromboembolic disease in those carrying factor V Leiden mutations is thought to increase 10-fold further when the subjects use oral contraceptives. 4 Elevated homocysteine was associated with a risk for stroke in one study 2~ but another found no increase in stroke risk associated with a common polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene, which in turn leads to increased serum homocysteine concentrations. 21 Platelet receptor genes have also been explored as candidates in association studies although their influence remains debatable. 22,23 Other logical candidates are genes coding for enzymes which metabolize medications used to treat stroke. Rates of metabolism by several of the CYP450 enzymes vary because of genetically determined polymorphisms. Recent data reveal that approximately 20% of the white population carries one of at least two different CYP450 point mutations which cause sensitivity to Warfarin. 24 This suggests that CYP2C9 genotypes may someday be helpful in planning initial Warfarin dosing.
Genetics and Pharmacogenetics of Related Risk Factors for Stroke Cardiovascular Disease A family history of cardiovascular disease is a risk factor for stroke.~ ~ Cardiac diseases have a large number of causes, including genetic. Mutations in ion channels, contractile proteins, structural proteins, and signaling molecules all have been identified as causal for cardiovascular diseasesY Genome wide linkage scans have revealed multiple loci that contribute to susceptibility for cardiovascular risk factors. The clinical c0urse of the congenital long QT syndrome (LQTS) can be predicted through genotypic analysis7 6 It is suggested that patients with LQTS because o f a sodium channel mutation (SCN5A) are better treated with class Ib sodium channel blockers, not beta-blockers (the current mainstay of therapy). 2 7 While these and other cardiac disorders might not directly relate to, a risk of stroke, they underscore the utility of such studies and give clues to possible additional targets ,for study in stroke.
Hypertension It is well known that hypertension is a major risk factor for stroke7 8 The risk of stroke is higher in hyper-
tensive than in nonhypertensive relatives of stroke patients, suggesting that underlying etiological factors are shared. 29 Single gene causes of hypertension suggest possible candidate genes for pharmocogenetic studies in stroke. These include the genes for glucocorticoid-remediable aldosteronism (GRA), an autosomal dominant cause of hypertension associated with cerebral hemorrhage, 3~ and Liddle's syndrome (aut0somal dominant hypertension with alkalosis and hypokalaemia), the latter of which is because of a mutation in a sodium channel subunit gene. 3~ In a genome scan on 490 hypertensive patients from 120 extended Icelandic families, linkage to Ch. 18q was found with a LOD score of 4.60, suggesting that a gene influencing hypertension risk lies therein. 32 A polymorphism in the gene coding for the cytoskeleton protein, alpha-adducin, has been linked to essential hypertension in hypertensive sibpairs; this gene is associated specifically with sodium sensitivity and responsiveness to diuretic therapy. 33 Angiotensin genotype appears to influence therapeutic response to treatment with ACE inhibitorsY Evidence for association of the ACE gene with hypertension and blood pressure in men, but not women, was found in a case control study of over 3,000 subjectsY However, in other studies, no significant difference was found in ischemic cerebrovascular disease between genotype classes of the ACE gene polymorphism in women or men, making these candidates less intriguing for the study of stroke. 36
Hyperlipidemia and Obesity It is not clear whether or not obesity or hyperlipidemia are independent risk factors for stroke, or contribute to other risks (including diabetes, hypertension), which in turn influence stroke. There is mounting evidence, however, that the genetics of lipid disorders will be importan t for stroke risk assessment. Although serum cholesterol traditionally has been considered a poor predictor of total stroke risk, very high levels of serum cholesterol seem to be a significant contributing factor? v Elevated serum cholesterol is associated positively with ischemic and negatively with hemorrhagic stroke risk. 38 Epidemiological evidence supports the relationship of lipids as a risk factor for ischemic stroke, and treatment of hyperlipidemia is often addressed in the context of stroke prevention. An increased serum lipoprotein(a) and intermediate density lipoprotein abnormalities, together with decreased high-density lipoprotein levels, are major risk factors for ischemic cerebrovascular disease, even in those with otherwise normal serum lipids and cholesterol. 39 Apolipoproteins are likely to be important in neurological illness, and the apolipoprotein (Apo) epsilon 4 allele (E4) is clearly a risk factor for Alzheimer's disease. 4~ ApoE4 may also be a predisposing genetic marker for ischemic cerebrovascular disease. 4~ The E2
Pharmacogenetics in Cerebrovascular Disease 9 Katrina Gwinn-Hardy and/or the E4 alleles may be risk factors for cerebral amyloid angiopathy independent of their influence on the risk for Alzheimer's disease, but this remains controversial. 42,43 Subjects with an ApoE2 or ApoE4 allele were found to be at greater risk for intracranial hemorrhage (ICH) independent of environmental risk factors in one study. 44 ApoA-I and ApoB alleles have been associated with a risk of severe carotid artery atherosclerosis in an elderly population, more so in African Americans and Whites than in Hispanics, although their influence on stroke remains to be discovered. 4s Polymorphisms in the ApoB-100 gene and the fatty acid-binding protein 2 gene have been identified, which influence not only insulin resistance and obesity in men 45,46 but also obesity and coronary artery, disease generally. 47 However, it is not clear that these in turn lead an increase in stroke.
Diabetes Diabetes, along with hypertension, is considered one of the modifiable risk factors for stroke 49 but it is not known if the genetic risks for diabetes contribute directly to a risk for stroke. Mutations in genes for insulin and insulin related genes have been shown to be causal for Mendelian type I diabetes. 5~ Studies of siblings and their HLA types have revealed a genetic component to type I diabetes generally. 52,53 It remains to be seen where these genetic features of diabetes overlap the genetic risk for stroke, if at all.
Pharmacogenetics and Genomics Many pharmaceutical companies are aware of the value of collecting genetic data during clinical trials and are in the process of doing so. 54,55 Single nucteotide polymorphisms (SNPs) of unknown function can be screened via microarray for a pattern associated with a drug response, which may ultimately be less cumbersome than using the traditional candidate gene approachY These studies are conceptually simpler than candidate gene studies, since, one need not make any assumptions about gene function to predict drug responsiveness using these data. Proteomics is the study of human proteins to understand their function, and will be the next step toward deciphering genes influence disease and treatment. It is suspected thafproteomics will provide additional information on treatment responses, which will further allow stratification of diseases into biologically meaningful categories.
45
Summary and Future Directions The field of genetics of neurological disorders includes a range from single gene Mendelian disorders to very complex (where multiple genetic factors of unknown influence are explored). Pharmacogenetics is on the complex end of this spectrum. Clearly, before pharmacogenetics can generally be brought into clinical practice, additional study is warranted. To elucidate pharmacogenetic factors in an increasingly sophisticated fashion, a large, diverse, and well-characterized sample and associated clinical database is needed. Pharmacogenetics research is bi-directional with clinical trials efforts: efficacy data collected during clinical trials can be correlated with genetic polymorphisms, which in turn will be useful to refine subject groups for treatment stratification analysis. Genotyping, including via microarray, can be used subsequently in clinical practice to predict drug responsiveness and safety profiles. It has been imagined that the tools of pharmacogenetics could allow a patient with a given diagnosis to undergo a genome scan, and have an appropriate medication chosen based on risk and efficacy, data derived via such genotyping. At this point, however, these ideas are in the realm of fantasy, and pharmacogenetics is in its infancy. Nonetheless, genotyping is likely to become an important tool for weighing treatment options in clinical practice in the future.
References 1. Weber WW: Populations and genetic polymorphisms. Mol Diagn 4:299-307, 1999 2. Urwyler A, Deufel T, McCarthy T, et al: Guidelines of molecular genetic detection of susceptibility to malignant hyperthermia. Br J Anesth 86:283-287, 2001 3. Ackermann MJ: The long QT syndrome. Pediatr Rev 19: 232-238, 1998 4. Vandeubrouke JP, Koster T, Bri6t E, et al: Increased risk of venous thrombosis in oral-contraceptive users who are carriers of factor V Leiden mutations. Lancet 344:14531457, 1994 5. Kapitany T, Meszaros K, Lenzinger E, et al: Genetic polymorphisms for drug metabolism (CYP2D6) and tardive dyskinesia in schizophrenia. Schizophrenia Res 32: 101-106, 1998 6. Gershon D: Microarray technology: An array of opportunities. Nature 416:885-891, 2002 7. Hardy J, Gwinn-Hardy K: Neurodegenerative disease: A different view of diagnosis. Mol Med Today 5:514-517, 1999 8. Hademos GJ, Alberts MJ, Awad I e t al: Advances in the genetics of cerebrovascular disease and stroke. Neurology 56:997-1008, 2001 9. Natowicz M, Kelley Rt: Mendelian etiologies of stroke. Ann Neurol 22:175-192, 1987
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10. Ruchoux MM, Brulin P, Brillault J, et al: Lessons from CADASIL. Ann NY Acad Sci 977:224-231, 2002 1 l. Kiely DK, Wolf PA, Cupples LA, et al: Familial aggregation of stroke. The Framingham study. Stroke 24:13661371, 1993 12. Ayala C, Greenlund KJ, Croft JB, et al: Racial/ethnic disparities in mortality by stroke subtype in the United States, 1995-1998. Am J Epidemiol 154:1057-1063, 2001 13. Kissela BM, Sauerbeck L, Woo D, et al: Subarachnoid hemorrhage: a preventable disease with a heritable component. Stroke 33:1321-1326, 2002 14. Gretarsdottir S, Sveinbjomsdottir S, Jonsson HH, et al: Localization of a susceptibility gene for common forms of stroke to 5qi2. Am J Hum Genet 70:593-603, 2002 15. Ridker PM, Hennekens CH, Lindpaintner K, et al: Mutation in the gene coding for coagulation factor V and the risk of myocardial infarction stroke, and venous thrombosis in apparently healthy men. N Engl J Med 332:912-917, 1995 16. Tatlisumak T, Syrjala M, Lndsberg P, et al: FV-ARG-506GLN-mutation-associated resistance to activated protein C in ischemic stroke. J Stroke Cerebrovasc Dis 5:192-196, 1995 17. Rosendaal Fr, Siscovick DS, Schwartz SM, et al: A common prothrombin variant (20210 G to A) increases the risk of myocardial infarction in young women. Blood 90:17471750, 1997 18. Longstreth WT, Rosendaal FR, Siscovick DS, et al: Risk of stroke in young women and two prothrombiti mutations: Factor V Leiden and prothrombin gene variant (G20210A). Stroke 29:577-580, 1998 19. Press RD, Liu XY, Beamer N, et al: Ischemic stroke in the elderly. Role of the common factor V mutation causing resistance to activated protein C. Stroke 27:44-48, 1996 20. Perry IJ, Refsum H, Morris RW, et al: Prospective study of serum total homocysteine concentrations and risk of stroke in middle-aged British men. Lancet 346:1395-1398, 1995 21. Markus HS, Ali N, Swaminathan R, et al: A common polymorphism in the methylenetetrahydrofolate reductase gene, homocysteine, and ischemic cerebrovascular disease. Stroke 28:1739-1743, 1997 22. Carlsson LE, Greinacher A, Spitzer C, et al: Polymorphisms of the human platelet antigens HPA-1,-HPA-2, HPA-3, and HPA-5 on the platelet receptors for fibrinogen (GPIIb/IIIa), von Willebrand factor (GPIb/IX) and collagen (GPIa/Iia) are not correlated with an increasedrisk for stroke. Stroke 28:1392-1395, 1997 23. Wagner KR, Giles WH, Johnson CJ, et al: Platelet glycoprotein receptor I!Ia polymorphism P1A2 and ischemic stroke risk: The Stroke prevention in young women study. Stroke 29:581-585, 1998 24. Aithal GP, Da~ CP, Kesteven PJL, et al: Association of the polymorphisms in the cytochrome P450 CYP2C9 with warfarin dose requirement and risk of bleeding complications. LanCet 353:717-719, 1999 25. Keating MT, Sanguinetti MC: Molecular genetic insights into cardiovascular disease. Science 272:681-685, 1996 26. Zareba W, Moss AJ, Schwartz P, et al: Influence of the genotype on the clinical course of the long-QT syndrome. N Engl J Med 339:960-965, 1998
27. Schwartz PJ, Priori SG, Locati EH, et al: Long QT syndrome patients with mutations of the SCN5A and HERG genes have differential responses to Na + channel blockage and to increases in heart rate: Implications for gene specific therapy. Circulation 92:3381-3386, 1995 28. Donnan GA, Davis SM, Thrift A: The role of blood pressure lowering before and after stroke. Curr Opin Neurol 16:81-86, 2003 Feb 29. Nicolaou M, DeStefano AL, Gavras I, et al: Genetic predisposition to stroke in relatives of hypertensives. Stroke 31:487-492, 2000 Feb 30. Lifton RP, Dluhy RG, Powers M, et al: A chimaeric 1 beta-hydroxytase/aldosterone synthase gene causes glucocorticoid-remediable aldosterism and human hypertension. Nature 355:262-265, 1992 31. Shimkets RA, Warnock DG, Bositis CM, et al: Liddle's syndrome: Heritable human hypertension causes by mutations in the beat-subunit of the epithelial sodium channel. Cell 79:407-414, 1994 32. Kristjansson K, Manolescu A, Kristinsson A, et al: Linkage of essential hypertension to chromosome 18q. Hypertension 39:1044-1049, 2002 33. Bianchi G, Tripodi G, Casari G, et al: Two point mutations within the adducin genes are involved in blood pressure variation. Proc Natl Acad Sci 91:3999-4003, 1994 34. Hingorani AD, Jia H, Stevens PA, et al: Renin-angiotensin system gene polymorphism influence blood pressure and the response to angiotensin converting enzyme inhibition. J Hypertens 13:1602-1609, 1995 35. O'Donnell CJ, Lindpaintner K, Larson MG, et al: Evidence for association and genetic linkage of the angiotensinconverting enzyme locus with hypertension and blood pressure in men but not women in the Framingham Heart Study. Circulation 97:1766-1772, 1998 36. Agerholm-Larsen B, Tybjaerg-Hansen A, Frikke-Schmidt R, et al: ACE gene polymorphism as a risk factor for ischemic cerebrovascular disease. Ann Intern Med 127: 346-355, t997 37. Postiglione A, Napoli C: Hyperlipidaemia and atherosclerotic cerebrovascular disease. Curt Opin Lipidol 6:236242, 1995 38. Ansell BJ: Cholesterol, stroke risk, and stroke prevention. Curt Atheroscler Rep 2:92-96, 2000 39. GorelickPB, Schneck M, Berglund LF, et al: Status of lipids as a risk factor for stroke. Neuroepidemiology 16: 107-115, 1997 40. Roses AD: Apolipoprotein E in neurology. Curt Opin Neurol 9:265-270, 1996 41. Pedro-Botet J, Senti M, Nogues X, et al: Lipoprotein and apolipoprotein profile in men with ischemic stroke, Role of lipoprotein(a), triglyceride-rich lipoproteins, and apolipoprotein E polymorphism. Stroke 23:1556-1562, 1992 42. Nicoll JA, Burnett C, Love S, et al: High frequency of apolipoprotein E epsilon 2 allele in hemorrhage due to cerebral amyloid :angiopathy. Ann Neurol 41:716-721, 1997 43. Greenberg SM, Rebeck GW, Vonsattel JP, et al: Apolipoprotein E epsilon 4 and cerebral hemorrhage associated with amyloid angiopathy. Ann Neurol 38:254-259, 1995 44. Woo D, Sauerbeck LR, Kissela BM, et al: Genetic and
Pharmacogenetics in Cerebrovascular Disease
45.
46.
47.
48.
49.
environmental risk factors for intracerebral hemorrhage: Preliminary results of a populations-based study. Stroke 33:1190-1196, 2002 Vohl MC, Tchernof A, Dionne FT, et al: The ApoB-100 gene EcoRI polymorphism influences the relationship between features o f the insulin resistance syndrome and the hyper-ApoB and dense LDL phenotype in men. Diabetes 45:1405-1411, 1996 Yamada K, Yan X, Ishiyama S, et al: Association between ala54the substation of the fatty acid-binding protein 2 gene with insulin resistance and intra abdominal fat thickness in Japanese men. Diabetologia 40:706-710, 1997 Hokanson JE: Lipoprotein lipase gene variants and risk of coronary disease-a quantitative analysis of populationbased studies (review). Int J Clin Lab Res 27:24-34, 1997 Jeng JS, Sacco RL, Kargman DE, et al: Apolipoproteins and carotid artery atherosclerosis in an elderly multiethnic population: The Northern Manhattan stroke study. Atherosclerosis 165:317-325, 2002 Sacco RL: Reducing the risk of stroke in diabetes: What
50.
51.
52.
53.
54. 55.
9
Katrina Gwinn-Harcly ' 4 7
have we learned that is new? Diabetes Obes Metab 4:$27$34, 2002 (suppl 1) Awata T, Kurihara S, Kikuchi C, et al: Evidence for association between the class 1 subset of the insulin gene minisatellite (IDDM 2 locus) and IDDM in the NIDDM. Diabetes 46:1725-1732, 1997 Yamagata K, Oda N, Kaisaki PJ, et al: Mutations in the hepatocyte nuclear factor-1 alpha gene in maturity onset diabetes of the young (MODY3). Nature 384:455-458, 1996 Davies JL, Kawaguchi Y, Bennett ST, et al: A genomewide search for human type 1 diabetes susceptibility genes. Nature 371:130-136, 1994 Fava D, Gardner S, Pyke D, Leslie RDG: Evidence that the age oat diagnosis of IDDM is genetically determined. Diabetes Care 21:925-929, 1998 Gtizey C, Spigset O: Genotyping of drug targets. Drug Saf 25:553-560, 2002 Black R: GSK bets on the genomic route to drag safety. Reactions Weekly 841:3, 2001
Pharmacogenetics in Cerebrovascular Disease KATRINA GWINN-HARDY Bethesda, Maryland
ABSTRACT The principles of pharmacogenetics are a longstanding component of clinical practice, in which the physician chooses therapy based on the profile of the patient's historic and diagnostic features, to maximize benefit and minimize adverse events. However, the tools of modern molecular biology have allowed increased sophistication to be applied to the profiling of patients to optimize treatment. While these tools are not yet available to the practicing clinician, an awareness of the concepts on which they are based is of interest, as they are likely to become available and 'widely used in the future. Keywords: pharmacogenetics, genetics, stroke, risk factors.
Although pharmacogenetics is the subject of considerable hype, the concepts underlying it are not new. For example, when a clinician considers treatment based on ethnicity or gender, family histo12r and/or allergies (all of which are influenced by genetic factors), he or she is using pharmacogenetic principles. Glucose-6-phosphate dehydrogenase (G6PD) deficiency, which can lead to adverse drug reactions, has long been known to be more common in African and Mediterranean people than in those of northern European origin.1 Malignant hyperthermia, 2 long QT syndrome 3 venous thromobembolic disease, 4 and tardive dyskinesia 5 among many other examples, have all been associated with underlying genetic risk factors. New tools such as DNA microarray technology, 6 high-output screening systems, and advanced bioinformatics, when combined with the infrastructures of large simple clinical trials, will lead to a better understanding of pharmacogenetics. Genetic causes of disease range from classic Mendelian (a single gene leads to disease) to complex (multiple genes contribute to risk for disease in combination with other genetic and/or environmental factors). While rare, single gene disorders are important, in part because they
elucidate pathways leading to disease. 7 Pharmacogenetic studies, however, are based on common genes of lesser influence. One method of identifying genetic risk factors is the candidate gene association study, in which a given polymorphism in a gene of interest is compared between cases or controls; if the polymorphism is more common in affected subjects, a contribution to risk for disease is implied. A candidate gene is usually selected because the gene product is intuitively related to the disease process.
Stroke Genetics and Pha rmacogenetics Many genetic influences on stroke and its risk factors have been established. 8 Single gene disorders that cause stroke include hemoglobinopathies, dyslipoproteinemias, and cardioembolic disorders. 9,1~ Family history of ischemic stroke is a major risk factor for the disease.9,11 Ethnicity is also a risk factor; age-standardized mortality rates for stroke is higher among African Americans than Whites.12 Family history is an independent risk factor for subarachnoid hemorrhage (SAH). 13 Most clinicians separate stroke into ischemic and hemorrhagic types as two broad categories (and those into subcategories), and one might surmise that such stratification would be important for gene discovery. The experience in stroke suggests the opposite; grouping all types of stroke together has been successful. A genome scan of 476 patients (from 179 extended Icelandic pedigrees) considered all types of -
From the National Institute of Neurological Disorders and Stroke, Bethesda, MD.
Address reprint requests to Katrina Gwinn-Hardy, MD, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892. E-mail: gwinnk @ninds.nih.gov. 9 2003 Elsevier Inc. All rights reserved.
1528-9931/03/0301-0008530.00/0 doi: 10.1053/scds.2003.00014
43
44
Seminars in Cerebrovascular Diseases and Stroke Vol. 3 No. 1 March 2003
stroke together, and revealed linkage to a 20 centiMorgan (cM) region on 5q12 where a gene for stroke is likely to lie. TM Genes related to the coagulation system are logical candidates for genetic susceptibility studies. Factor V Leiden and prothrombin (Factor II) mutations are putative risk factors for stroke. 15-19The higher risk for thromboembolic disease in those carrying factor V Leiden mutations is thought to increase 10-fold further when the subjects use oral contraceptives. 4 Elevated homocysteine was associated with a risk for stroke in one study 2~ but another found no increase in stroke risk associated with a common polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene, which in turn leads to increased serum homocysteine concentrations. 21 Platelet receptor genes have also been explored as candidates in association studies although their influence remains debatable. 22,23 Other logical candidates are genes coding for enzymes which metabolize medications used to treat stroke. Rates of metabolism by several of the CYP450 enzymes vary because of genetically determined polymorphisms. Recent data reveal that approximately 20% of the white population carries one of at least two different CYP450 point mutations which cause sensitivity to Warfarin. 24 This suggests that CYP2C9 genotypes may someday be helpful in planning initial Warfarin dosing.
Genetics and Pharmacogenetics of Related Risk Factors for Stroke Cardiovascular Disease A family history of cardiovascular disease is a risk factor for stroke.~ ~ Cardiac diseases have a large number of causes, including genetic. Mutations in ion channels, contractile proteins, structural proteins, and signaling molecules all have been identified as causal for cardiovascular diseasesY Genome wide linkage scans have revealed multiple loci that contribute to susceptibility for cardiovascular risk factors. The clinical c0urse of the congenital long QT syndrome (LQTS) can be predicted through genotypic analysis7 6 It is suggested that patients with LQTS because o f a sodium channel mutation (SCN5A) are better treated with class Ib sodium channel blockers, not beta-blockers (the current mainstay of therapy). 2 7 While these and other cardiac disorders might not directly relate to, a risk of stroke, they underscore the utility of such studies and give clues to possible additional targets ,for study in stroke.
Hypertension It is well known that hypertension is a major risk factor for stroke7 8 The risk of stroke is higher in hyper-
tensive than in nonhypertensive relatives of stroke patients, suggesting that underlying etiological factors are shared. 29 Single gene causes of hypertension suggest possible candidate genes for pharmocogenetic studies in stroke. These include the genes for glucocorticoid-remediable aldosteronism (GRA), an autosomal dominant cause of hypertension associated with cerebral hemorrhage, 3~ and Liddle's syndrome (aut0somal dominant hypertension with alkalosis and hypokalaemia), the latter of which is because of a mutation in a sodium channel subunit gene. 3~ In a genome scan on 490 hypertensive patients from 120 extended Icelandic families, linkage to Ch. 18q was found with a LOD score of 4.60, suggesting that a gene influencing hypertension risk lies therein. 32 A polymorphism in the gene coding for the cytoskeleton protein, alpha-adducin, has been linked to essential hypertension in hypertensive sibpairs; this gene is associated specifically with sodium sensitivity and responsiveness to diuretic therapy. 33 Angiotensin genotype appears to influence therapeutic response to treatment with ACE inhibitorsY Evidence for association of the ACE gene with hypertension and blood pressure in men, but not women, was found in a case control study of over 3,000 subjectsY However, in other studies, no significant difference was found in ischemic cerebrovascular disease between genotype classes of the ACE gene polymorphism in women or men, making these candidates less intriguing for the study of stroke. 36
Hyperlipidemia and Obesity It is not clear whether or not obesity or hyperlipidemia are independent risk factors for stroke, or contribute to other risks (including diabetes, hypertension), which in turn influence stroke. There is mounting evidence, however, that the genetics of lipid disorders will be importan t for stroke risk assessment. Although serum cholesterol traditionally has been considered a poor predictor of total stroke risk, very high levels of serum cholesterol seem to be a significant contributing factor? v Elevated serum cholesterol is associated positively with ischemic and negatively with hemorrhagic stroke risk. 38 Epidemiological evidence supports the relationship of lipids as a risk factor for ischemic stroke, and treatment of hyperlipidemia is often addressed in the context of stroke prevention. An increased serum lipoprotein(a) and intermediate density lipoprotein abnormalities, together with decreased high-density lipoprotein levels, are major risk factors for ischemic cerebrovascular disease, even in those with otherwise normal serum lipids and cholesterol. 39 Apolipoproteins are likely to be important in neurological illness, and the apolipoprotein (Apo) epsilon 4 allele (E4) is clearly a risk factor for Alzheimer's disease. 4~ ApoE4 may also be a predisposing genetic marker for ischemic cerebrovascular disease. 4~ The E2
Pharmacogenetics in Cerebrovascular Disease 9 Katrina Gwinn-Hardy and/or the E4 alleles may be risk factors for cerebral amyloid angiopathy independent of their influence on the risk for Alzheimer's disease, but this remains controversial. 42,43 Subjects with an ApoE2 or ApoE4 allele were found to be at greater risk for intracranial hemorrhage (ICH) independent of environmental risk factors in one study. 44 ApoA-I and ApoB alleles have been associated with a risk of severe carotid artery atherosclerosis in an elderly population, more so in African Americans and Whites than in Hispanics, although their influence on stroke remains to be discovered. 4s Polymorphisms in the ApoB-100 gene and the fatty acid-binding protein 2 gene have been identified, which influence not only insulin resistance and obesity in men 45,46 but also obesity and coronary artery, disease generally. 47 However, it is not clear that these in turn lead an increase in stroke.
Diabetes Diabetes, along with hypertension, is considered one of the modifiable risk factors for stroke 49 but it is not known if the genetic risks for diabetes contribute directly to a risk for stroke. Mutations in genes for insulin and insulin related genes have been shown to be causal for Mendelian type I diabetes. 5~ Studies of siblings and their HLA types have revealed a genetic component to type I diabetes generally. 52,53 It remains to be seen where these genetic features of diabetes overlap the genetic risk for stroke, if at all.
Pharmacogenetics and Genomics Many pharmaceutical companies are aware of the value of collecting genetic data during clinical trials and are in the process of doing so. 54,55 Single nucteotide polymorphisms (SNPs) of unknown function can be screened via microarray for a pattern associated with a drug response, which may ultimately be less cumbersome than using the traditional candidate gene approachY These studies are conceptually simpler than candidate gene studies, since, one need not make any assumptions about gene function to predict drug responsiveness using these data. Proteomics is the study of human proteins to understand their function, and will be the next step toward deciphering genes influence disease and treatment. It is suspected thafproteomics will provide additional information on treatment responses, which will further allow stratification of diseases into biologically meaningful categories.
45
Summary and Future Directions The field of genetics of neurological disorders includes a range from single gene Mendelian disorders to very complex (where multiple genetic factors of unknown influence are explored). Pharmacogenetics is on the complex end of this spectrum. Clearly, before pharmacogenetics can generally be brought into clinical practice, additional study is warranted. To elucidate pharmacogenetic factors in an increasingly sophisticated fashion, a large, diverse, and well-characterized sample and associated clinical database is needed. Pharmacogenetics research is bi-directional with clinical trials efforts: efficacy data collected during clinical trials can be correlated with genetic polymorphisms, which in turn will be useful to refine subject groups for treatment stratification analysis. Genotyping, including via microarray, can be used subsequently in clinical practice to predict drug responsiveness and safety profiles. It has been imagined that the tools of pharmacogenetics could allow a patient with a given diagnosis to undergo a genome scan, and have an appropriate medication chosen based on risk and efficacy, data derived via such genotyping. At this point, however, these ideas are in the realm of fantasy, and pharmacogenetics is in its infancy. Nonetheless, genotyping is likely to become an important tool for weighing treatment options in clinical practice in the future.
References 1. Weber WW: Populations and genetic polymorphisms. Mol Diagn 4:299-307, 1999 2. Urwyler A, Deufel T, McCarthy T, et al: Guidelines of molecular genetic detection of susceptibility to malignant hyperthermia. Br J Anesth 86:283-287, 2001 3. Ackermann MJ: The long QT syndrome. Pediatr Rev 19: 232-238, 1998 4. Vandeubrouke JP, Koster T, Bri6t E, et al: Increased risk of venous thrombosis in oral-contraceptive users who are carriers of factor V Leiden mutations. Lancet 344:14531457, 1994 5. Kapitany T, Meszaros K, Lenzinger E, et al: Genetic polymorphisms for drug metabolism (CYP2D6) and tardive dyskinesia in schizophrenia. Schizophrenia Res 32: 101-106, 1998 6. Gershon D: Microarray technology: An array of opportunities. Nature 416:885-891, 2002 7. Hardy J, Gwinn-Hardy K: Neurodegenerative disease: A different view of diagnosis. Mol Med Today 5:514-517, 1999 8. Hademos GJ, Alberts MJ, Awad I e t al: Advances in the genetics of cerebrovascular disease and stroke. Neurology 56:997-1008, 2001 9. Natowicz M, Kelley Rt: Mendelian etiologies of stroke. Ann Neurol 22:175-192, 1987
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10. Ruchoux MM, Brulin P, Brillault J, et al: Lessons from CADASIL. Ann NY Acad Sci 977:224-231, 2002 1 l. Kiely DK, Wolf PA, Cupples LA, et al: Familial aggregation of stroke. The Framingham study. Stroke 24:13661371, 1993 12. Ayala C, Greenlund KJ, Croft JB, et al: Racial/ethnic disparities in mortality by stroke subtype in the United States, 1995-1998. Am J Epidemiol 154:1057-1063, 2001 13. Kissela BM, Sauerbeck L, Woo D, et al: Subarachnoid hemorrhage: a preventable disease with a heritable component. Stroke 33:1321-1326, 2002 14. Gretarsdottir S, Sveinbjomsdottir S, Jonsson HH, et al: Localization of a susceptibility gene for common forms of stroke to 5qi2. Am J Hum Genet 70:593-603, 2002 15. Ridker PM, Hennekens CH, Lindpaintner K, et al: Mutation in the gene coding for coagulation factor V and the risk of myocardial infarction stroke, and venous thrombosis in apparently healthy men. N Engl J Med 332:912-917, 1995 16. Tatlisumak T, Syrjala M, Lndsberg P, et al: FV-ARG-506GLN-mutation-associated resistance to activated protein C in ischemic stroke. J Stroke Cerebrovasc Dis 5:192-196, 1995 17. Rosendaal Fr, Siscovick DS, Schwartz SM, et al: A common prothrombin variant (20210 G to A) increases the risk of myocardial infarction in young women. Blood 90:17471750, 1997 18. Longstreth WT, Rosendaal FR, Siscovick DS, et al: Risk of stroke in young women and two prothrombiti mutations: Factor V Leiden and prothrombin gene variant (G20210A). Stroke 29:577-580, 1998 19. Press RD, Liu XY, Beamer N, et al: Ischemic stroke in the elderly. Role of the common factor V mutation causing resistance to activated protein C. Stroke 27:44-48, 1996 20. Perry IJ, Refsum H, Morris RW, et al: Prospective study of serum total homocysteine concentrations and risk of stroke in middle-aged British men. Lancet 346:1395-1398, 1995 21. Markus HS, Ali N, Swaminathan R, et al: A common polymorphism in the methylenetetrahydrofolate reductase gene, homocysteine, and ischemic cerebrovascular disease. Stroke 28:1739-1743, 1997 22. Carlsson LE, Greinacher A, Spitzer C, et al: Polymorphisms of the human platelet antigens HPA-1,-HPA-2, HPA-3, and HPA-5 on the platelet receptors for fibrinogen (GPIIb/IIIa), von Willebrand factor (GPIb/IX) and collagen (GPIa/Iia) are not correlated with an increasedrisk for stroke. Stroke 28:1392-1395, 1997 23. Wagner KR, Giles WH, Johnson CJ, et al: Platelet glycoprotein receptor I!Ia polymorphism P1A2 and ischemic stroke risk: The Stroke prevention in young women study. Stroke 29:581-585, 1998 24. Aithal GP, Da~ CP, Kesteven PJL, et al: Association of the polymorphisms in the cytochrome P450 CYP2C9 with warfarin dose requirement and risk of bleeding complications. LanCet 353:717-719, 1999 25. Keating MT, Sanguinetti MC: Molecular genetic insights into cardiovascular disease. Science 272:681-685, 1996 26. Zareba W, Moss AJ, Schwartz P, et al: Influence of the genotype on the clinical course of the long-QT syndrome. N Engl J Med 339:960-965, 1998
27. Schwartz PJ, Priori SG, Locati EH, et al: Long QT syndrome patients with mutations of the SCN5A and HERG genes have differential responses to Na + channel blockage and to increases in heart rate: Implications for gene specific therapy. Circulation 92:3381-3386, 1995 28. Donnan GA, Davis SM, Thrift A: The role of blood pressure lowering before and after stroke. Curr Opin Neurol 16:81-86, 2003 Feb 29. Nicolaou M, DeStefano AL, Gavras I, et al: Genetic predisposition to stroke in relatives of hypertensives. Stroke 31:487-492, 2000 Feb 30. Lifton RP, Dluhy RG, Powers M, et al: A chimaeric 1 beta-hydroxytase/aldosterone synthase gene causes glucocorticoid-remediable aldosterism and human hypertension. Nature 355:262-265, 1992 31. Shimkets RA, Warnock DG, Bositis CM, et al: Liddle's syndrome: Heritable human hypertension causes by mutations in the beat-subunit of the epithelial sodium channel. Cell 79:407-414, 1994 32. Kristjansson K, Manolescu A, Kristinsson A, et al: Linkage of essential hypertension to chromosome 18q. Hypertension 39:1044-1049, 2002 33. Bianchi G, Tripodi G, Casari G, et al: Two point mutations within the adducin genes are involved in blood pressure variation. Proc Natl Acad Sci 91:3999-4003, 1994 34. Hingorani AD, Jia H, Stevens PA, et al: Renin-angiotensin system gene polymorphism influence blood pressure and the response to angiotensin converting enzyme inhibition. J Hypertens 13:1602-1609, 1995 35. O'Donnell CJ, Lindpaintner K, Larson MG, et al: Evidence for association and genetic linkage of the angiotensinconverting enzyme locus with hypertension and blood pressure in men but not women in the Framingham Heart Study. Circulation 97:1766-1772, 1998 36. Agerholm-Larsen B, Tybjaerg-Hansen A, Frikke-Schmidt R, et al: ACE gene polymorphism as a risk factor for ischemic cerebrovascular disease. Ann Intern Med 127: 346-355, t997 37. Postiglione A, Napoli C: Hyperlipidaemia and atherosclerotic cerebrovascular disease. Curt Opin Lipidol 6:236242, 1995 38. Ansell BJ: Cholesterol, stroke risk, and stroke prevention. Curt Atheroscler Rep 2:92-96, 2000 39. GorelickPB, Schneck M, Berglund LF, et al: Status of lipids as a risk factor for stroke. Neuroepidemiology 16: 107-115, 1997 40. Roses AD: Apolipoprotein E in neurology. Curt Opin Neurol 9:265-270, 1996 41. Pedro-Botet J, Senti M, Nogues X, et al: Lipoprotein and apolipoprotein profile in men with ischemic stroke, Role of lipoprotein(a), triglyceride-rich lipoproteins, and apolipoprotein E polymorphism. Stroke 23:1556-1562, 1992 42. Nicoll JA, Burnett C, Love S, et al: High frequency of apolipoprotein E epsilon 2 allele in hemorrhage due to cerebral amyloid :angiopathy. Ann Neurol 41:716-721, 1997 43. Greenberg SM, Rebeck GW, Vonsattel JP, et al: Apolipoprotein E epsilon 4 and cerebral hemorrhage associated with amyloid angiopathy. Ann Neurol 38:254-259, 1995 44. Woo D, Sauerbeck LR, Kissela BM, et al: Genetic and
Pharmacogenetics in Cerebrovascular Disease
45.
46.
47.
48.
49.
environmental risk factors for intracerebral hemorrhage: Preliminary results of a populations-based study. Stroke 33:1190-1196, 2002 Vohl MC, Tchernof A, Dionne FT, et al: The ApoB-100 gene EcoRI polymorphism influences the relationship between features o f the insulin resistance syndrome and the hyper-ApoB and dense LDL phenotype in men. Diabetes 45:1405-1411, 1996 Yamada K, Yan X, Ishiyama S, et al: Association between ala54the substation of the fatty acid-binding protein 2 gene with insulin resistance and intra abdominal fat thickness in Japanese men. Diabetologia 40:706-710, 1997 Hokanson JE: Lipoprotein lipase gene variants and risk of coronary disease-a quantitative analysis of populationbased studies (review). Int J Clin Lab Res 27:24-34, 1997 Jeng JS, Sacco RL, Kargman DE, et al: Apolipoproteins and carotid artery atherosclerosis in an elderly multiethnic population: The Northern Manhattan stroke study. Atherosclerosis 165:317-325, 2002 Sacco RL: Reducing the risk of stroke in diabetes: What
50.
51.
52.
53.
54. 55.
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Katrina Gwinn-Harcly ' 4 7
have we learned that is new? Diabetes Obes Metab 4:$27$34, 2002 (suppl 1) Awata T, Kurihara S, Kikuchi C, et al: Evidence for association between the class 1 subset of the insulin gene minisatellite (IDDM 2 locus) and IDDM in the NIDDM. Diabetes 46:1725-1732, 1997 Yamagata K, Oda N, Kaisaki PJ, et al: Mutations in the hepatocyte nuclear factor-1 alpha gene in maturity onset diabetes of the young (MODY3). Nature 384:455-458, 1996 Davies JL, Kawaguchi Y, Bennett ST, et al: A genomewide search for human type 1 diabetes susceptibility genes. Nature 371:130-136, 1994 Fava D, Gardner S, Pyke D, Leslie RDG: Evidence that the age oat diagnosis of IDDM is genetically determined. Diabetes Care 21:925-929, 1998 Gtizey C, Spigset O: Genotyping of drug targets. Drug Saf 25:553-560, 2002 Black R: GSK bets on the genomic route to drag safety. Reactions Weekly 841:3, 2001