title: Smoking and family history and risk of aneurysmal subarachnoid hemorrhage.
abstract: OBJECTIVE
  Smoking and family history of aneurysmal subarachnoid hemorrhage (aSAH) are independent risk factors for aSAH. Using a population-based case-control study of hemorrhagic stroke, we hypothesized that having both a first-degree relative with a brain aneurysm or SAH (+FH) and current smoking interact to increase the risk of aSAH.
  
  
  METHODS
  Cases of aneurysmal SAH were prospectively recruited from all 17 hospitals in the five-county region around the University of Cincinnati. Controls were identified by random digit dialing. Controls were matched to cases of aSAH by age (+/-5 years), race, and sex. Conditional multiple logistic regression was used to identify independent risk factors. For deviation from the additive model, the interaction constant ratio test was used.
  
  
  RESULTS
  A total of 339 cases of aSAH were matched to 1,016 controls. Compared to current nonsmokers with no first-degree relatives with aSAH (-FH), the odds ratio (OR) for aSAH for current nonsmokers with +FH was 2.5 (95% confidence interval [CI] 0.9-6.9); for current smokers with -FH, OR = 3.1 (95% CI 2.2-4.4); and for current smokers with +FH, OR = 6.4 (95% CI 3.1-13. 2). The interaction constant ratio, which measured the deviation from the additive model, was significant: 2.19 (95% CI 0.80-5.99). The lower bound of the 95% CI >0.5 signifies a departure from the additive model.
  
  
  CONCLUSIONS
  Evidence of a gene-environment interaction with smoking exists for aneurysmal subarachnoid hemorrhage. This finding is important to counseling family members and for screening of intracranial aneurysm (IA) as well as the design and interpretation of genetic epidemiology of IA studies.
authors.affiliation: Department of Neurology, University of Cincinnati College of Medicine, 260 Stetson Street ML 0525, Cincinnati, OH 45267-0525, USA. Daniel.woo@uc.edu
authors.forename: D
authors.initials: D
authors.lastname: Woo
authors.forename: J
authors.initials: J
authors.lastname: Khoury
authors.forename: M M
authors.initials: MM
authors.lastname: Haverbusch
authors.forename: P
authors.initials: P
authors.lastname: Sekar
authors.forename: M L
authors.initials: ML
authors.lastname: Flaherty
authors.forename: D O
authors.initials: DO
authors.lastname: Kleindorfer
authors.forename: B M
authors.initials: BM
authors.lastname: Kissela
authors.forename: C J
authors.initials: CJ
authors.lastname: Moomaw
authors.forename: R
authors.initials: R
authors.lastname: Deka
authors.forename: J P
authors.initials: JP
authors.lastname: Broderick
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D018672:Community Health Planning; D016001:Confidence Intervals; D005192:Family Health; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012189:Retrospective Studies; D012306:Risk; D012307:Risk Factors; D012907:Smoking; D013345:Subarachnoid Hemorrhage / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics*