Aetiological overlap between obsessive-compulsive and depressive symptoms: a longitudinal twin study in adolescents and adults.
BACKGROUND
Depression is commonly co-morbid with obsessive-compulsive disorder (OCD). However, it is unknown whether depression is a functional consequence of OCD or whether these disorders share a common genetic aetiology. This longitudinal twin study compared these two hypotheses.


METHODS
Data were drawn from a longitudinal sample of adolescent twins and siblings (n = 2651; Genesis 12-19 study) and from a cross-sectional sample of adult twins (n = 4920). The longitudinal phenotypic associations between OCD symptoms (OCS) and depressive symptoms were examined using a cross-lag model. Multivariate twin analyses were performed to explore the genetic and environmental contributions to the cross-sectional and longitudinal relationship between OCS and depressive symptoms.


RESULTS
In the longitudinal phenotypic analyses, OCS at time 1 (wave 2 of the Genesis 12-19 study) predicted depressive symptoms at time 2 (wave 3 of the Genesis 12-19 study) to a similar extent to which depressive symptoms at time 1 predicted OCS at time 2. Cross-sectional twin analyses in both samples indicated that common genetic factors explained 52-65% of the phenotypic correlation between OCS and depressive symptoms. The proportion of the phenotypic correlation due to common non-shared environmental factors was considerably smaller (35%). In the adolescent sample, the longitudinal association between OCS at time 1 and subsequent depressive symptoms was accounted for by the genetic association between OCS and depressive symptoms at time 1. There was no significant environmental association between OCS and later depressive symptoms.


CONCLUSIONS
The present findings show that OCS and depressive symptoms co-occur primarily due to shared genetic factors and suggest that genetic, rather than environmental, effects account for the longitudinal relationship between OCS and depressive symptoms.
Department of Child and Adolescent Psychiatry, King's College London, Institute of Psychiatry, London, UK.
K
K
Bolhuis
Social, Genetic and Developmental Psychiatry Centre, King's College London, Institute of Psychiatry, London, UK.
T A
TA
McAdams
Department of Psychosis Studies, Institute of Psychiatry, King's College London, Institute of Psychiatry, London, UK.
B
B
Monzani
Department of Psychology, Goldsmiths, University of London, London, UK.
A M
AM
Gregory
Department of Psychosis Studies, Institute of Psychiatry, King's College London, Institute of Psychiatry, London, UK.
D
D
Mataix-Cols
Department of Child and Adolescent Psychiatry, King's College London, Institute of Psychiatry, London, UK.
A
A
Stringaris
Social, Genetic and Developmental Psychiatry Centre, King's College London, Institute of Psychiatry, London, UK.
T C
TC
Eley
D000293:Adolescent; D000328:Adult; D003863:Depression / Q000209:etiology / Q000235:genetics*; D004200:Diseases in Twins / Q000209:etiology / Q000235:genetics*; D005260:Female; D058685:Genetic Pleiotropy / Q000235:genetics; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009771:Obsessive-Compulsive Disorder / Q000209:etiology / Q000235:genetics*; D012042:Registries; D035781:Siblings; D055815:Young Adult