| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
(Stroke. 2003;34:1364.)
© 2003 American Heart Association, Inc.
Original Contributions |
From the Department of Clinical Neurosciences, St Georges Hospital Medical School, London, UK.
Correspondence to Dr Paula Jerrard-Dunne, Department of Clinical Neurosciences, St Georges Hospital Medical School, Cranmer Terrace, Tooting, London SW17 0RE, UK. E-mail pjerrard{at}sghms.ac.uk
| Abstract |
|---|
|
|
|---|
Methods One thousand consecutive white subjects with ischemic stroke and 800 white controls matched for age and sex were recruited. A first-degree family history of stroke and myocardial infarction was obtained by structured interview. Stroke subtype was determined with the use of modified Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria.
Results A family history of stroke at
65 years was a significant risk factor for large-vessel disease (odds ratio [OR], 2.24; 95% CI, 1.49 to 3.36; P<0.001) and for small-vessel disease (OR, 1.93; 95% CI, 1.25 to 2.97; P=0.003). When only cases aged
65 years were considered, these ORs increased to 2.93 (95% CI, 1.68 to 5.13) (P<0.001) and 3.15 (95% CI, 1.81 to 5.50) (P<0.001), respectively. No significant associations were seen for cardioembolic stroke or stroke of undetermined etiology.
Conclusions A family history of vascular disease is an independent risk factor for both large-vessel atherosclerosis and small-vessel disease, especially in cases presenting before age 65 years. The estimated sample sizes for case-control studies illustrate how candidate gene studies for ischemic stroke might be made more effective by focusing on these specific phenotypes, in which the genetic component of the disease appears to be strongest.
Key Words: cerebral infarction epidemiology genetics risk factors stroke classification
| Introduction |
|---|
|
|
|---|
Recent advances in neuroimaging have made it easier to identify underlying disease mechanisms and appropriately classify stroke. It is likely that the genetic risk profile at the molecular level differs according to ischemic stroke subtype. For example, the factors leading to carotid atherothrombosis may be different from those that predispose to cerebrovascular small-vessel disease or to cardioembolism.
While certain genes, such as those that predispose to cerebral ischemia, may increase ischemic stroke risk in all the major subtypes, other genetic factors that predispose to underlying disease mechanisms, such as carotid atherosclerosis or microangiopathy, may be relatively more important in specific etiologic subtypes. An example of this is seen in the monogenic stroke disorder CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), in which the notch 3 mutation predisposes specifically to lacunar infarction.5
Future candidate gene studies investigating the genetic basis of ischemic stroke may be more successful if they focus on selected patient groups in which genetic factors are most important. In particular, it has been suggested that familial factors are more important in individuals presenting with stroke at a young age4 and in certain stroke subtypes.5 Using a positive family history as a marker of increased genetic risk, in this study we sought to determine the familial component of different ischemic stroke subtypes, specifically focusing on younger age groups that are likely to have the greatest genetic component.
| Subjects and Methods |
|---|
|
|
|---|
Risk factors documented in both cases and controls included age, sex, smoking status, hypertension, diabetes, hyperlipidemia, and ischemic heart disease. Smoking status was categorized as current smoker (patient admission or
1 cigarette per day in the past 12 months), ex-smoker, or never-smoker. Hypertension was defined as pharmacological treatment for hypertension or systolic blood pressure
160 mm Hg and/or diastolic blood pressure
95 mm Hg persisting >7 days after the acute event (World Health Organization classification).6 Diabetes was defined as reported or medical notes record of either diet-controlled, oral hypoglycemictreated, or insulin-treated diabetes. Hyperlipidemia was defined as pharmacological treatment or total serum cholesterol
6.5 mmol/L. Ischemic heart disease was defined as self-reported or hospital record of MI or angina. Details were corroborated by patients medical records. Relatives medical records were not available to validate family history data. Informed consent was obtained from all subjects, and the local ethics committee approved the study.
Stroke Subtyping
All cases were examined by a neurologist and underwent neuroimaging (CT and/or MRI) and an ECG. Ninety-five percent had extracranial carotid and vertebral duplex ultrasound. Echocardiography (31%) and MR angiography and/or transcranial Doppler ultrasound (9%) were performed when clinically indicated. With the use of clinical, radiological, cardiac, and ultrasound test results, each case was assessed according to modified Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria7 to determine stroke subtype. Large-vessel disease was defined as >50% stenosis or occlusion of an appropriate major brain artery or branch cortical artery in the absence of sources of cardiac embolism. Small-vessel disease was defined as a clinical lacunar syndrome with a relevant infarct of <1.5 cm in the absence of a cardioembolic source or carotid stenosis >50%. Cardioembolic stroke was defined as the presence of atrial fibrillation, MI in the past 6 months, or a high-risk source of embolism identified on echocardiogram according to TOAST criteria.7 Stroke of undetermined etiology was used when no etiologic source could be identified. A tandem (combined) classification was used when >1 etiology was identified. Stroke of other determined etiology included those with carotid dissection, vasculopathies, and hematologic disorders. Subjects with a monogenic cause of stroke, eg, CADASIL, were excluded from the study. Tandem strokes and strokes of other determined etiology accounted for only a small number of ischemic strokes, and therefore analysis by subtype was confined to the 4 major subtypes: large-vessel disease, small-vessel disease, cardioembolic stroke, and ischemic stroke of undetermined etiology.
Statistical Methods
Differences between groups were examined with the
2 test to calculate proportions and with Students t test for continuous variables. Multivariate odds ratios (ORs) and 95% CIs for a family history of stroke or MI in cases versus controls were calculated with the use of binary logistic regression analysis controlling for age, sex, arterial hypertension, diabetes mellitus, serum cholesterol, and smoking status. ORs were calculated for overall ischemic stroke and for the 4 major subtypes. Because there is some evidence to suggest that genetic factors are more important in younger individuals, a prespecified analysis of families with disease onset at a young age (
65 years) was also performed. To determine whether the effect of a positive family history was dependent on age, the population was then stratified according to the age of onset of stroke (in 5-year categories), and ORs were recalculated.
To determine potential implications for planning future candidate gene studies, we created a model using the observed multivariate ORs to estimate the sample size requirements for case-control studies with specific stroke subtypes and age groups compared with ischemic stroke overall. Sample sizes were estimated on the basis of standard tests for the difference between proportions based on the anticipated OR.8 For this model, sample sizes required to detect an effect equal to the magnitude of the observed multivariate OR were calculated, with a 2-tailed significance level of 0.05 and a power of 0.8, with the assumption of candidate gene allele frequencies of 5%, 10%, or 15%. The software used for sample size calculations was DSTPLAN version 4.2 (University of Texas, MD Anderson Cancer Center, 2000).
| Results |
|---|
|
|
|---|
There were no significant differences between cases and controls with regard to age, sex, or number of siblings in the overall analysis. Arterial hypertension, diabetes mellitus, ischemic heart disease, hyperlipidemia, and current smoking were all significantly more common in cases than in controls (Table 1). The distribution of stroke subtypes was as follows: large-vessel disease, 262 (26.2%); small-vessel disease, 232 (23.2%); cardioembolic, 118 (11.8%); ischemic stroke of undetermined etiology, 296 (29.6%); tandem, 69 (6.9%); and other determined etiology, 23 (2.3%). Demographic and risk factor profiles according to the 4 major stroke subtypes are given in Table 1. Subjects with cardioembolic stroke were older and had a more equal sex distribution than controls. A greater proportion of subjects with stroke of undetermined etiology were female compared with the other stroke subtypes.
|
The relationship between family history parameters and ischemic stroke is shown in Table 2. The strongest risk factors for stroke were a family history of stroke at
65 years (OR, 1.69; 95% CI, 1.25 to 2.29; P=0.001) and a family history of MI at any age (OR, 1.57; 95% CI, 1.29 to 1.91; P<0.001). Additional adjustment for age, sex, and vascular risk factors only slightly attenuated these ORs, which remained significant (Table 2). The observed relationships were similar when maternal, paternal, or sibling risk was studied individually; for example, the OR for ischemic stroke at any age conferred by a paternal history of stroke at
65 years was 1.90 (95% CI, 1.23 to 2.93) compared with 1.63 (95% CI, 1.04 to 2.54) for a maternal history.
|
Table 3 presents the ORs for both a family history of stroke at
65 years and a family history of MI at any age, according to stroke subtype. The strongest associations with family history parameters were seen for large-vessel disease (multivariate OR, 2.32; 95% CI, 1.68 to 3.21; P<0.001 for a family history of MI; multivariate OR, 1.67; 95% CI, 1.08 to 2.66; P=0.021 for a family history of stroke at
65 years). The relationship between large-vessel disease and family history of stroke at a young age was significant regardless of the age group analyzed, although the strength of the relationship increased progressively as the age at which the stroke occurred decreased. An OR of 2.34 (95% CI, 1.21 to 4.52) (P=0.011) was seen for stroke occurring at age
65 years (Table 4).
|
|
Small-vessel disease was less strongly associated with a family history of MI (multivariate OR, 1.46; 95% CI, 1.05 to 2.03; P=0.025). The association with a family history of stroke at
65 years was just outside significance on multivariate analysis (multivariate OR, 1.49; 95% CI, 0.94 to 2.37; P=0.088) (Table 3). For small-vessel disease, a significant interaction was found between age and a family history of stroke at
65 years (P for interaction=0.015). The ORs progressively increased as age decreased, and for cases aged
65 years the multivariate OR was 2.69 (95% CI, 1.46 to 4.96) (P=0.002). When individuals aged >65 years were included, this association was greatly weakened (Table 4). In contrast to the findings for large- and small-vessel disease, no significant associations were seen for cardioembolic stroke or for ischemic stroke of undetermined etiology. (Table 3).
Table 5 shows estimated sample sizes required to detect an effect equal to the observed multivariate ORs. With the use of this model and assumption of an allele frequency of 10%, a case-control study including all unselected ischemic stroke cases would require a sample size of 1481 cases and 1481 controls. Focusing on specific stroke subtypes considerably reduced the estimated sample sizes. Including either large- or small-vessel disease cases of all ages would reduce the number of cases to 542 and 946, respectively. Further confining the study to subjects with onset of stroke at a young age (
65 years) would have a major impact on sample size, with n=205 for all ischemic stroke and n=175 and n=123 for large- and small-vessel disease, respectively.
|
| Discussion |
|---|
|
|
|---|
65 years), in whom the genetic component of the disease appears to be strongest.
Previous studies examining the role of a positive family history in ischemic stroke risk have yielded conflicting results. The strongest evidence comes from twin concordance studies, which found a 2- to 4-fold increase in stroke risk in monozygotic versus dizygotic twin pairs.1,2 Prospective cohort studies have found a family history of stroke to be predictive of future stroke,3,4,9,10 and numerous case-control studies have shown positive associations.1113 In contrast, others, including a large prospective cohort study of >13 000 subjects, have been negative.1416 Positive results were more often seen in selected subgroups, for example, in younger subjects17 or in subjects with a family history of disease onset at a young age,4 suggesting that the extent to which genetic factors contribute to stroke risk may be age dependent. This is consistent with the findings of this study, in which positive associations were strongest among younger probands, and a positive association was seen for a family history of stroke at
65 years but not for a family history of stroke at any age.
While it has been proposed that defining specific subtypes may be key in elucidating the genetic contribution to stroke risk,18 few studies to date have examined the familial component of different etiologic subtypes. In a sample of 310 subjects with ischemic stroke, Meschia et al19 found no relationship between a positive family history of stroke and proband stroke subtype. However, this study did not include a control population and may therefore have been underpowered. A more recent case-control study (421 cases and 239 controls) found that both large- and small-vessel strokes were associated with a positive family history of stroke, with no association seen for cardioembolic stroke or for stroke of undetermined etiology, consistent with the findings of our study.12
Because stroke is the end result of a number of pathologically different processes, it is possible that many genes, each conferring a small amount of risk, are involved in influencing the end phenotype. Conventional case-control candidate gene studies may not be sufficiently powerful to detect the contribution of an individual disease allele since, to date, this approach has not yielded consistent results.5 Our modeling data, estimating sample sizes for specific stroke subtypes, suggest that using these phenotypes may be an effective way to increase power in case-control studies. Recent studies examining the role of genetic factors in specific stroke subtypes further support this hypothesis. For example, it has been suggested that a deletion polymorphism in the angiotensin-converting enzyme gene may be a specific risk factor for lacunar but not other stroke subtypes20 by predisposing to lipohyalinosis. The apolipoprotein E4 allele and the AA genotype of the ß-fibrinogen G/A-455 polymorphism were found to be risk factors for large-vessel disease but not other stroke subtypes, possibly mediated via an increased risk of atherosclerosis and atherothrombosis.21
Other mechanisms, including familial aggregation of stroke risk factors, cannot be excluded as a potential explanation for the findings of this study. Hypertension, dyslipidemia, and diabetes mellitus have all been shown to aggregate in families affected by stroke.2224 Although adjustment for vascular risk factors attenuated the observed associations, a positive family history remained an independent predictor of large-vessel disease and of small-vessel disease in younger subjects. This suggests that aggregation of risk factors cannot completely explain the relationship and that additional genetic factors may be involved.
The familial contribution to vascular disease is likely to reflect both shared genetic load and environmental exposures. The strong association seen between stroke and family history of MI in this study suggests that certain inherited etiologic factors are common to both diseases, for example, a genetic predisposition to arterial atherosclerosis in the case of large-vessel disease or to shared risk factors such as hypertension in the case of small-vessel disease. A trend was also seen toward an association between a family history of MI and cardioembolic stroke, which may reflect a shared familial risk for ischemic heart disease. The nonsignificant OR may have been affected by the lower number of cardioembolic strokes in the cohort compared with other stroke subtypes. The lack of association between a family history of stroke and cardioembolism may be a consequence of the heterogeneous etiology of the cardioembolic source, which may, for example, include rheumatic valvular disease, ischemic heart disease, and nonischemic cardiomyopathies.
A strength of this study is that the hospital-based cohort was extensively investigated, which permitted accurate stroke subtyping. However, this was at the expense of the exclusion of community stroke cases. Limitations of this study include possible family information bias, whereby cases are more likely to recall a relative affected by the same illness. Relatives medical records were not available to validate family history data, and it was not possible to distinguish between ischemic and hemorrhagic strokes at interview. However, if anything, the inclusion of hemorrhagic strokes would be expected to weaken the observed associations.
In summary, we found that a positive family history of vascular disease was an independent risk factor for both large-vessel atherosclerosis and small-vessel disease. This relationship was especially strong in individuals aged
65 years. In contrast, no association was seen with either cardioembolic stroke or stroke of undetermined etiology. The data modeling sample sizes suggest that studies investigating the genetic basis of polygenic ischemic stroke may be more effective if they focus on these specific etiologic subtypes and on younger age groups, which appear to have a particularly strong familial component of their stroke risk.
| Acknowledgments |
|---|
Received October 8, 2002; revision received November 25, 2002; accepted December 17, 2002.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
H. S. Markus Genes, endothelial function and cerebral small vessel disease in man Exp Physiol, January 1, 2008; 93(1): 121 - 127. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Lee and M. Kong An Interactive Association of Common Sequence Variants in the Neuropeptide Y Gene With Susceptibility to Ischemic Stroke Stroke, October 1, 2007; 38(10): 2663 - 2669. [Abstract] [Full Text] [PDF] |
||||
![]() |
W. Lalouschek, G. Endler, M. Schillinger, K. Hsieh, W. Lang, S. Cheng, P. Bauer, O. Wagner, and C. Mannhalter Candidate Genetic Risk Factors of Stroke: Results of a Multilocus Genotyping Assay Clin. Chem., April 1, 2007; 53(4): 600 - 605. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. G. Wiklund, W. M. Brown, T. G. Brott, B. Stegmayr, R. D. Brown Jr, S. Nilsson-Ardnor, J. A. Hardy, B. M. Kissela, A. Singleton, D. Holmberg, et al. Lack of aggregation of ischemic stroke subtypes within affected sibling pairs Neurology, February 6, 2007; 68(6): 427 - 431. [Abstract] [Full Text] [PDF] |
||||
![]() |
M.J.E. van Rijn, A. J.C. Slooter, A. F.C. Schut, A. Isaacs, Y. S. Aulchenko, P. J.L.M. Snijders, L. J. Kappelle, J. C. van Swieten, B. A. Oostra, and C. M. van Duijn Familial aggregation, the PDE4D gene, and ischemic stroke in a genetically isolated population Neurology, October 25, 2005; 65(8): 1203 - 1209. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Dichgans and H. S. Markus Genetic Association Studies in Stroke: Methodological Issues and Proposed Standard Criteria Stroke, September 1, 2005; 36(9): 2027 - 2031. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. K. Lynch, C. J. Han, L. E. Nee, and K. B. Nelson Prothrombotic Factors in Children With Stroke or Porencephaly Pediatrics, August 1, 2005; 116(2): 447 - 453. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Gormley, S. Bevan, A. Hassan, and H. S. Markus Polymorphisms in Genes of the Endothelin System and Cerebral Small-Vessel Disease Stroke, August 1, 2005; 36(8): 1656 - 1660. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Jood, C. Ladenvall, A. Rosengren, C. Blomstrand, and C. Jern Family History in Ischemic Stroke Before 70 Years of Age: The Sahlgrenska Academy Study on Ischemic Stroke Stroke, July 1, 2005; 36(7): 1383 - 1387. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Moskau, A. Golla, C. Grothe, M. Boes, C. Pohl, and T. Klockgether Heritability of Carotid Artery Atherosclerotic Lesions: An Ultrasound Study in 154 Families Stroke, January 1, 2005; 36(1): 5 - 8. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. F. Meschia Clinically Translated Ischemic Stroke Genomics Stroke, November 1, 2004; 35(11_suppl_1): 2735 - 2739. [Abstract] [Full Text] [PDF] |
||||
![]() |
H Markus Genes for stroke J. Neurol. Neurosurg. Psychiatry, September 1, 2004; 75(9): 1229 - 1231. [Full Text] [PDF] |
||||
![]() |
A. Slowik, T. Dziedzic, W. Turaj, J. Pera, L. Glodzik-Sobanska, P. Szermer, M. T. Malecki, D. A. Figlewicz, and A. Szczudlik A2 Alelle of GpIIIa Gene Is a Risk Factor for Stroke Caused by Large-Vessel Disease in Males Stroke, July 1, 2004; 35(7): 1589 - 1593. [Abstract] [Full Text] [PDF] |
||||
![]() |
U.G.R. Schulz, E. Flossmann, and P.M. Rothwell Heritability of Ischemic Stroke in Relation to Age, Vascular Risk Factors, and Subtypes of Incident Stroke in Population-Based Studies Stroke, April 1, 2004; 35(4): 819 - 824. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. J. Alberts Genetics of Cerebrovascular Disease Stroke, February 1, 2004; 35(2): 342 - 344. [Full Text] [PDF] |
||||
![]() |
E. Flossmann, U. G.R. Schulz, and P. M. Rothwell Systematic Review of Methods and Results of Studies of the Genetic Epidemiology of Ischemic Stroke Stroke, January 1, 2004; 35(1): 212 - 227. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Stroke Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 2003 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |