title: Genetic influences on developmental smoking trajectories.
abstract: OBJECTIVE
  To investigate the relative contribution of genetic and environmental factors on smoking trajectory membership and to test whether individual smoking trajectories represent phenotypical thresholds of increasing genetic risk along a common genetic liability dimension.
  
  
  METHODS
  Prospective study of a birth cohort of female like-sex twin pairs.
  
  
  METHODS
  Participants completed diagnostic interview surveys four times from adolescence (average age 16) to young adulthood (average age 25).
  
  
  METHODS
  Female twins who had smoked ≥100 cigarettes life-time (n = 1466 regular smokers).
  
  
  METHODS
  Number of cigarettes smoked per day during the heaviest period of smoking (two waves) or during the past 12 months (two waves).
  
  
  RESULTS
  A four-trajectory class solution provided the best fit to cigarette consumption data and was characterized by low (n = 564, 38.47%), moderate (n = 366, 24.97%) and high-level smokers (n = 197, 13.44%), and smokers who increased their smoking from adolescence to young adulthood (n =339, 23.12%). The best genetic model fit was a three-category model that comprised the low, a combined increasing + moderate and high trajectories. This trajectory categorization was heritable (72.7%), with no evidence for significant contribution from shared environmental factors.
  
  
  CONCLUSIONS
  The way in which smoking patterns develop in adolescence has a high level of heritability.
authors.affiliation: Department of Psychiatry, Washington University School of Medicine, St Louis, MO, USA. schlaggc@psychiatry.wustl.edu
authors.forename: Christina N
authors.initials: CN
authors.lastname: Lessov-Schlaggar
authors.forename: Sean D
authors.initials: SD
authors.lastname: Kristjansson
authors.forename: Kathleen K
authors.initials: KK
authors.lastname: Bucholz
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Heath
authors.forename: Pamela A F
authors.initials: PA
authors.lastname: Madden
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D004777:Environment; D005260:Female; D005838:Genotype; D006801:Humans; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000235:genetics*; D019966:Substance-Related Disorders / Q000235:genetics; D055815:Young Adult