The structure of genetic and environmental risk factors for syndromal and subsyndromal common DSM-IV axis I and all axis II disorders

Abstract

Objective: The authors sought to clarify the structure of the genetic and environmental risk factors for 22 DSM-IV disorders: 12 common axis I disorders and all 10 axis II disorders.

Method: The authors examined syndromal and subsyndromal axis I diagnoses and five categories reflecting number of endorsed criteria for axis II disorders in 2,111 personally interviewed young adult members of the Norwegian Institute of Public Health Twin Panel.

Results: Four correlated genetic factors were identified: axis I internalizing, axis II internalizing, axis I externalizing, and axis II externalizing. Factors 1 and 2 and factors 3 and 4 were moderately correlated, supporting the importance of the internalizing-externalizing distinction. Five disorders had substantial loadings on two factors: borderline personality disorder (factors 3 and 4), somatoform disorder (factors 1 and 2), paranoid and dependent personality disorders (factors 2 and 4), and eating disorders (factors 1 and 4). Three correlated environmental factors were identified: axis II disorders, axis I internalizing disorders, and externalizing disorders versus anxiety disorders.

Conclusions: Common axis I and II psychiatric disorders have a coherent underlying genetic structure that reflects two major dimensions: internalizing versus externalizing, and axis I versus axis II. The underlying structure of environmental influences is quite different. The organization of common psychiatric disorders into coherent groups results largely from genetic, not environmental, factors. These results should be interpreted in the context of unavoidable limitations of current statistical methods applied to this number of diagnostic categories.

FIGURE 1

Parameter Estimates From the Best Overall Model for Genetic Factors for Syndromal and Subsyndromal Common DSM-IV Axis I and All Axis II Disorders^{a a}Four factors were identified using an oblique geomin rotation. Only those paths are depicted that account for more than 10% of the genetic variance in disease liability—that is, have a path estimate of ≥0.316. For all path estimates in the model, see Table 3. PD=personality disorder.

FIGURE 2

Parameter Estimates From the Best Overall Model for Individual-Specific Environmental Factors for Syndromal and Subsyndromal Common DSM-IV Axis I and All Axis II Disorders^{a a}Three factors were identified using an oblique geomin rotation. Only those paths are depicted that account for more than 10% of the individual-specific environmental variance in disease liability—that is, have a path estimate of ≥0.316. For all path estimates in the model, see Table 4. Two disorders—eating disorders and specific phobia—are not represented in this figure because they failed to load substantially on any of the three identified factors. PD=personality disorder.