Saturday, 15 January 2005 - 10:00 AM

This presentation is part of: Environmental Influences on Psychological Distress

Genetic and Environmental Characteristics of Panic-Depression Comorbidity versus Single Disorders in a Twin Sample

Purpose: Guided by the hypothesis that early adversity can heighten the stress response, creating an enhanced vulnerability to anxiety and depression, this analysis compares the family environments and experience of traumatic events of individuals with lifetime comorbidity to those with a single disorder. It investigates the clustering of traumatic events in a twin sample, the family background factors associated with trauma clusters, and the relative effects of trauma, genetic effects, and family background factors on risk for three mutually-exclusive categories of disorder: (1) panic attack or disorder, (2) depression, and (3) comorbid depression and panic.

Methods: Information about childhood environment, lifetime experience of traumatic events, and mental disorder was elicited from a sample of Australian twins via diagnostic interview. Latent class analysis was used to define trauma classes characterized by different types and frequencies of trauma. Age at onset of first trauma and of first disorder were examined for each class using lifetables and Kaplan-Meier survival curves. Logistic regression was used to examine the family background factors associated with each class. Genetic effects were modeled as the interaction between zygosity and cotwin status on disorder. Multinomial logistic regression was used to examine associations of trauma classes, family background factors, and genetic effects with each category of disorder.

Results: Clustering of trauma: Ninety-five percent of the sample was concentrated in three trauma classes characterized by low rates of trauma or by nonassaultive events such as life-threatening accidents or witnessing injury or killing. The remaining five percent comprised three trauma classes characterized by experience of assaultive events such as rape, assault, and childhood physical and sexual abuse. This five percent was younger at first trauma and experienced a greater number of traumatic events. They had higher rates of all categories of disorder, particularly comorbidity, and had an earlier age at onset of disorder. Family background factors associated with trauma clusters: Parental alcohol problems were common to three trauma groups. Factors common to assaultive trauma categories were not having a close relationship with parents, frequent conflict with parents, and not being allowed to bring friends home. Effects on risk for disorder: Four of the trauma classes, genetic effects, and several family background factors had independent effects on risk for disorder. In the single disorder groups, trauma classes, genetic effects, and family background factors had similar effects. Trauma classes had larger effects on risk for comorbid depression and panic than for either disorder alone. Genetic effects on risk for disorder and the effects of family background factors were similar across diagnostic categories.

Implications: This analysis suggests that early adversity does enhance vulnerability to mental disorder, and particularly to comorbidity. The increased risk for disorder among individuals with comorbid conditions in this sample arises more from the effects of trauma than from genetic predisposition. This has implications for treatment of individuals with comorbid conditions, who may benefit from combined psycho- and pharmacotherapy to a greater degree than individuals with single disorders.

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