Using trajectory analyses to refine phenotype for genetic association: conduct problems and the serotonin transporter (5HTTLPR).
BACKGROUND
Conduct disorder is a serious, relatively common disorder of childhood and adolescence. Findings from genetic association studies searching for genetic determinants of the liability toward such behaviors have been inconsistent. One possible explanation for differential results is that most studies define phenotype from a single assessment; for many adolescents conduct problems decrease in severity over time, whereas for others such behaviors persist. Therefore, longitudinal datasets offer the opportunity to refine phenotype.


METHODS
We used Caucasians that were first assessed during adolescence from the National Youth Survey Family Study. Nine waves of data were used to create latent growth trajectories and test for associations between trajectory class and 5HTTLPR genotype.


RESULTS
For the full sample, 5HTTLPR was not associated with conduct problem phenotypes. However, the short (s) allele was associated with chronic conduct problems in females; a nominally significant sex by 5HTTLPR genotype interaction was noted.


CONCLUSIONS
Longitudinal studies provide unique opportunities for phenotypic refinement and such techniques, with large samples, may be useful for phenotypic definition with other study designs, such as whole genome association studies.
Sakai
Joseph T
JT
University of Colorado Denver, Aurora, Colorado, USA. joseph.sakai@ucdenver.edu
Boardman
Jason D
JD
Gelhorn
Heather L
HL
Smolen
Andrew
A
Corley
Robin P
RP
Huizinga
David
D
Menard
Scott
S
Hewitt
John K
JK
Stallings
Michael C
MC
D000293:Adolescent; D001483:Base Sequence; D002648:Child; D019955:Conduct Disorder / Q000235:genetics*; D017931:DNA Primers; D005260:Female; D005787:Gene Frequency; D006801:Humans; D008297:Male; D010641:Phenotype; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics*; D011795:Surveys and Questionnaires
D017931:DNA Primers; D050486:Serotonin Plasma Membrane Transport Proteins