| Abstract: | To investigate environmental factors that protect against or exacerbate obsessive-compulsive (OC) symptoms, we selected 25
monozygotic (MZ) twin pairs discordant, 17 MZ twin pairs concordant high and 34 MZ pairs concordant low on OC symptoms from
a large longitudinal Dutch sample of adult twin pairs and their family members, applying stringent criteria for OC symptomatology.
Data were collected on psychopathology, family structure, health, lifestyle, birth complications and life events. Unique environmental
factors were studied using within-discordant MZ pair comparisons, whereas between-concordant MZ pair comparisons were used
to study environmental factors that are shared by the twins of an MZ pair. The high-scoring MZ twins of the discordant group
reported more life events (especially sexual abuse) than their low-scoring twin-siblings. The between-pair comparisons showed
lower birth weight in the discordant MZ pairs than in the concordant MZ pairs. Further, the concordant high MZ pairs as well
as their spouses had a lower educational level than the two other groups. On scale scores of anxious-depression, neuroticism,
and somatic complaints, concordant high MZ pairs showed highest scores, and the discordant MZ pairs scored intermediate, except
for neuroticism, on which the high-scoring twins of discordant MZ pairs were equal to the concordant high pairs. Discordance
on psychological scale scores between the concordant MZ pairs was evident from 1991 onward, and within the discordant MZ pairs
from 1997 onward, confirming previous reports of an association of early-onset OC symptoms with higher genetic load. Parent
scores of OC symptoms and anxious-depression suggested intermediate genetic load in the discordant MZ group. In conclusion,
this study reports on both unique and shared environmental factors associated with OC symptomatology. Whether these factors
operate in addition to or in interaction with genetic disposition is to be elucidated in future studies.
Edited by Tatiana Foroud. |
