title: Birth weight predicts risk of cardiovascular disease within dizygotic but not monozygotic twin pairs: a large population-based co-twin-control study.
abstract: BACKGROUND
  The widely reported inverse association between birth weight and risk of cardiovascular disease (CVD) has sparked theories about early life determinants of adult disease. Within-twin-pair analysis provides a unique opportunity to investigate whether factors shared within twin pairs influence the association.
  
  
  RESULTS
  In a population-based cohort of like-sexed twins with known zygosity born in Sweden from 1926 to 1958, disease-discordant twin pairs were identified through linkage to the National Inpatient and Cause of Death registers between 1973 and 2006. Co-twin-control analyses were performed on twins discordant for cardiovascular disease (n=3884), coronary heart disease (n=2668), and stroke (n=1372). Overall, inverse associations between birth weight and risk of cardiovascular diseases were seen within dizygotic but not monozygotic twin pairs. In dizygotic twins, the odds ratios for a 1-kg within-pair increase in birth weight were 0.74 (95% confidence interval, 0.56 to 0.98) for coronary heart disease and 0.57 (95% confidence interval, 0.37 to 0.88) for stroke. Conversely, no statistically significant associations were found within monozygotic twins (for coronary heart disease: odds ratio, 1.10; 95% confidence interval, 0.73 to 1.68; for stroke: odds ratio, 0.92; 95% confidence interval, 0.48 to 1.80).
  
  
  CONCLUSIONS
  We found an association between birth weight and risk of cardiovascular disease within disease-discordant dizygotic but not monozygotic twin pairs. This indicates that the association between birth weight and cardiovascular disease could be a result of common causes, and that factors that vary within dizygotic but not monozygotic twin pairs may help identify them.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, SE-171 77, Sweden. sara.oberg@ki.se
authors.forename: Sara
authors.initials: S
authors.lastname: Oberg
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
authors.forename: Sven
authors.initials: S
authors.lastname: Sandin
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: Anastasia N
authors.initials: AN
authors.lastname: Iliadou
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001724:Birth Weight; D002318:Cardiovascular Diseases / Q000235:genetics* / Q000401:mortality*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008505:Medical Staff, Hospital / Q000706:statistics & numerical data; D008875:Middle Aged; D011237:Predictive Value of Tests; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic