Genetic variation in the serotonin transporter gene influences adult attachment style

Objective: To ascertain if the 5-HTTLPR short allele was associated with an insecure style of attachment in a mixed sample of healthy subjects and psychiatric patients. Method: Three hundred and thirty five adults (222 healthy subjects and 113 psychiatric patients) were genotyped for the 5-HTTLPR serotonin transporter polymorphism. Adult attachment style was assessed by using the Relationship Questionnaire (RQ). The personality trait of harm avoidance was assessed by using the Temperament and Character Inventory (TCI). The depression subscale of the Profile of Mood States (POMS-D) was used to assess mood state. Harm avoidance and depression were measured to control their potential confounding effects on the relationship between the 5-HTTLPR serotonin transporter polymorphism and adult attachment style.Results: We found a significant association between insecure attachment and the 5-HTTLPR short allele. Separate analyses in the subcohorts of healthy subjects and psychiatric patients confirmed the association between attachment style and 5-HTTLPR. Such an association was not a byproduct of the relationship between the serotonin transporter polymorphism and neuroticism or negative affectivity because insecure attachment, but not the harm avoidance scale of the TCI, was associated with the short variant of 5-HTTLPR. Moreover, inclusion of harm avoidance and depressive symptoms into a multiple regression model did not weaken the significant correlation between the 5-HTTLPR and insecure attachment. The effect size seen in our study (Cramer’s phi = 0.15-0.21 approximately corresponding to Cohen’s d = 0.30-0.40) compares favorably to those reported in previous studies of association between the 5-HTTLPR polymorphism and personality traits. Conclusions: This study suggests that part of the variation in adult attachment styles can be accounted for by genetic differences among individuals