Students of human nature have long grappled with questions about the replication of parents' traits into their offspring. Nonmedical writings have alluded to the fact that "sins" may be transmitted from parents to children. However, the first extensive elaboration on the impact of parents' neuroses on their children came in the late 1800s from the emerging field of psychoanalysis. All subsequent schools of psychology examining trauma have been concerned with the handing down of neurotic traits. It was only in the post-Holocaust era that a consistent literature on the intergenerational effects of parents' traumas emerged. Soon after the description of the Holocaust syndrome by Niederland (1961), Rakoff et al. (1966) reported on the transmission of the effects of the Holocaust trauma to the "second generation." Since then, several hundred articles on intergenerational transmission--mainly limited to clinical cases and anecdotal reports--have been published, raising criticisms about the initial lack of systematic empirical studies. This initial paucity of systematic research was partly due to a lack of consensus about what was being transmitted. There were early hints of a certain complex of symptoms or even specific psychopathology in children of Holocaust survivors (Barocas and Barocas, 1973).

Meanwhile, pointing to the heterogeneity of this group, Danieli (1981) identified four subtypes of families of Holocaust survivors: victim families, numb families, fighter families and families of "those who made it." In a seminal study, Solomon et al. (1988) examined Israeli soldiers who developed posttraumatic stress disorder during the Lebanese war and found that soldiers who were offspring of Holocaust survivors had a more protracted course of PTSD. Thus, the existence of a factor of vulnerability carried by healthy children of survivors was raised. Nader (1998) reported similar findings in children whose parents experienced significant traumata in life. Such children were more likely to present symptoms of PTSD after witnessing a violent incident.

Drawing on findings that repeated trauma exposure may alter the responsiveness of the hypothalamus-pituitary-adrenocortical axis even before the onset of PTSD, Yehuda et al. (1998) found that healthy offspring of Holocaust survivors are more likely to develop PTSD after traumatic events and report a larger number of symptoms. Similarly, Novac and Huber-Schneider (1998) reported increased comorbidity in previously healthy children of survivors who were seen in a psychiatric clinic for anxiety and depressive disorders. The authors hypothesized on the different mechanisms of transmission of trauma.

Other studies have further confirmed that offspring of Holocaust survivors are more vulnerable to psychological distress after developing breast cancer (Baider et al., 2000) and that healthy children of war veterans may show abnormalities in the Stroop Color Test (Motta et al., 1997). Danieli (1998) also covered a large number of studies in detail, including animal models for transmission.

The importance of this subject has also been recognized by the International Society of Traumatic Stress Studies (ISTSS), with the founding and maintaining of a Special Interest Area Group on Intergenerational Transmission of Trauma and Resiliency. At the annual ISTSS meetings, there are an increasing number of presentations on intergenerational transmission. There are also progressively more reports of psychopathology in the "third generation" (i.e., grandchildren) of Holocaust survivors.

In clinical practice, patients with parents suffering with PTSD often describe damaged, preoccupied parents who are emotionally limited. Symptoms in parents such as traumatic reliving, emotional numbing and dissociative phenomena do not help a child develop a reasonable sense of safety and predictability in the world. These parents are also less able to respond optimally during usual developmental crises and help the world to be more comprehensible to the child. The parent suffering with PTSD also has difficulty modeling a healthy sense of identity and autonomy, appropriate self-soothing mechanisms and affect regulation, and maintaining a balanced perspective when life challenges arise. Instead, they can model catastrophic or inappropriately numbed and disassociated responses. Therefore, the parent's high levels of anxiety can significantly interfere with the child's developmental progress.

Children's self-image and object relations are also obviously affected by their image of their parents. Parents' success in coping and being resilient determines whether the child can be proud, ashamed or confused about their parents.