title: Planning genetic studies in human stroke: sample size estimates based on family history data.
abstract: BACKGROUND
  Identification of stroke risk genes in humans has relied on case-control methods to determine the association between candidate genes and disease. Alternative approaches include linkage analysis using affected sibling pairs, transmission disequilibrium testing (TDT), and sibling TDT (S-TDT). Despite theoretical benefits, the feasibility of these methods in stroke remains unknown.
  
  
  METHODS
  Family history was determined in 727 patients with ischemic stroke and 623 control subjects. These data were used to estimate the number of stroke patients required for the different study designs.
  
  
  RESULTS
  A family history of any stroke occurring at < or =65 years was an independent risk factor for ischemic stroke at all ages (OR 1.47, 95% CI 1.02 to 2.12, p = 0.04) and a stronger risk factor for young (< or =65 years) ischemic stroke (OR 2.25, 95% CI 1.43 to 3.55, p < 0.0001). For early-onset ischemic stroke, the sibling risk ratio was estimated to be 3.08. Assuming three major stroke loci, collection of 953 affected sibling pairs (both < or =65 years) would be needed for a linkage study, and 115,472 ischemic stroke patients would have to be screened to achieve this sample size from the authors' population. The predicted sample sizes for association studies to detect a gene conferring an OR of 2.0 were case-control methodology (414), TDT (414), and S-TDT (617), which would require screening of 820, 31,680, and 3,062 cases.
  
  
  CONCLUSIONS
  Alternative genetic approaches are feasible, but TDT and linkage studies using the affected sib-pair methodology may require large multicenter collaborations. S-TDT approaches appear more practical. These estimates will aid in planning of such studies.
authors.affiliation: Department of Clinical Neurosciences, St. George's Hospital Medical School, London, United Kingdom.
authors.forename: Ahamad
authors.initials: A
authors.lastname: Hassan
authors.forename: Pak C
authors.initials: PC
authors.lastname: Sham
authors.forename: Hugh S
authors.initials: HS
authors.lastname: Markus
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D016001:Confidence Intervals; D005260:Female; D008040:Genetic Linkage / Q000235:genetics; D005820:Genetic Testing / Q000379:methods*; D006801:Humans; D015810:Linkage Disequilibrium / Q000235:genetics; D008297:Male; D008875:Middle Aged; D009679:Nuclear Family; D016017:Odds Ratio; D010375:Pedigree; D012307:Risk Factors; D018401:Sample Size; D020521:Stroke / Q000453:epidemiology* / Q000235:genetics*