title: Heritability of carotid intima-media thickness: a twin study.
abstract: OBJECTIVE
  To estimate the heritability of carotid intima-media thickness (IMT), a surrogate marker for atherosclerosis, independent of traditional coronary risk factors.
  
  
  RESULTS
  We performed a classical twin study of carotid IMT using 98 middle-aged male twin pairs, 58 monozygotic (MZ) and 40 dizygotic (DZ) pairs, from the Vietnam Era Twin Registry. All twins were free of overt cardiovascular disease. Carotid IMT was measured by ultrasound. Bivariate and multivariate analyses were used to determine the association between traditional cardiovascular risk factors and carotid IMT. Intraclass correlation coefficients and genetic modeling techniques were used to determine the relative contributions of genes and environment to the variation in carotid IMT. In our sample, the mean of the maximum carotid IMT was 0.75+/-0.11. Age, systolic blood pressure and HDL were significantly associated with carotid IMT. The intraclass correlation coefficient for carotid IMT was larger in MZ (0.66; 95% confidence interval [CI], 0.62-0.69) than in DZ twins (0.37; 95% CI, 0.29-0.44), and the unadjusted heritability was 0.69 (95% CI, 0.54-0.79). After adjusting for traditional coronary risk factors, the heritability of carotid IMT was slightly reduced but still of considerable magnitude (0.59; 95% CI, 0.39-0.73).
  
  
  CONCLUSIONS
  Genetic factors have a substantial influence on the variation of carotid IMT. Most of this genetic effect occurs through pathways independent of traditional coronary risk factors.
authors.affiliation: Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30306, United States.
authors.forename: Jinying
authors.initials: J
authors.lastname: Zhao
authors.forename: Faiz A
authors.initials: FA
authors.lastname: Cheema
authors.forename: J Douglas
authors.initials: JD
authors.lastname: Bremner
authors.forename: Jack
authors.initials: J
authors.lastname: Goldberg
authors.forename: Shaoyong
authors.initials: S
authors.lastname: Su
authors.forename: Harold
authors.initials: H
authors.lastname: Snieder
authors.forename: Carisa
authors.initials: C
authors.lastname: Maisano
authors.forename: Linda
authors.initials: L
authors.lastname: Jones
authors.forename: Farhan
authors.initials: F
authors.lastname: Javed
authors.forename: Nancy
authors.initials: N
authors.lastname: Murrah
authors.forename: Ngoc-Anh
authors.initials: NA
authors.lastname: Le
authors.forename: Viola
authors.initials: V
authors.lastname: Vaccarino
mesh_terms: D050197:Atherosclerosis / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000235:genetics*; D002339:Carotid Arteries / Q000000981:diagnostic imaging / Q000473:pathology*; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012042:Registries; D017539:Tunica Intima / Q000000981:diagnostic imaging / Q000473:pathology*; D017540:Tunica Media / Q000000981:diagnostic imaging / Q000473:pathology*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D014463:Ultrasonography; D014481:United States / Q000453:epidemiology