These twin studies also provide information about whether indirect associations exist between early trauma, such as childhood sexual abuse, and risk of psychiatric disorder. For example, children who are abused are more likely to come from high-risk family backgrounds (e.g., a family with an alcoholic parent), and therefore are likely to be exposed to other environmental factors that may also predict increased risk of psychopathology. This interpretation is supported by the observation that in twin pairs where only one twin has been abused, the nonabused twin still is more likely to report a history of psychiatric disorder as an adult than are twins from families where neither twin has been abused (Nelson et al. 2002). Such an increased risk would be expected if additional familial environmental risk factors for psychiatric disorder existed that were more common in families where child abuse occurred.
