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Keywords:

  • Heritability;
  • growth mixture models;
  • liability threshold models;
  • smoking trajectories;
  • substance use;
  • twins.

ABSTRACT

Aims  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.

Design  Prospective study of a birth cohort of female like-sex twin pairs.

Setting  Participants completed diagnostic interview surveys four times from adolescence (average age 16) to young adulthood (average age 25).

Participants  Female twins who had smoked ≥100 cigarettes life-time (n = 1466 regular smokers).

Measurements  Number of cigarettes smoked per day during the heaviest period of smoking (two waves) or during the past 12 months (two waves).

Findings  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.