Susceptibility to PTSD, Anxiety, Depression Hereditary

Caroline Cassels

December 22, 2008

December 22, 2008 — The genetic makeup of some individuals makes them substantially more vulnerable than others to develop symptoms of posttraumatic stress disorder (PTSD), anxiety, and depression.

A unique study that tracked individuals from 12 multigenerational families exposed to a massive earthquake in Armenia in 1988 found that 41% of the variation of PTSD symptoms was due to genetic factors and that 61% of the variation of depressive symptoms and 66% of anxiety symptoms were attributable to genetics.

"This was a study of multigenerational family members — parents and offspring, grandparents and grandchildren, siblings, and so on — and we found that the genetic makeup of some of these individuals renders them more vulnerable to develop PTSD, anxiety, and depressive symptoms," principal investigator Armen Goenjian, MD, from the University of California, Los Angeles department of psychiatry and biobehavioral sciences, said in a statement.

Furthermore, said Dr. Goenjian, the study suggests that a large percentage of genes are shared between these disorders — a finding that tracks with clinical experience.

"For example, in clinical practice, the therapist will often discover that patients who come in for treatment of depression have coexisting anxiety. Our findings show that a substantial portion of the coexistence can be explained on the basis of shared genes and not just environmental factors such as upbringing," he said.

The study is published in the December issue of Psychiatric Genetics.

Unique Study

According to the investigators, known risk factors for PTSD include female sex, past history and family history of anxiety, and prior exposure to traumatic experiences. Studies in twins have also suggested a link between heritability in PTSD and anxiety and PTSD and depression.

However, none of the research done to date has been able to assess heritability of PTSD symptoms.

"It's very hard to do family studies on PTSD, because typically only single individuals, not whole families, are exposed to a particular trauma. In our study, we were able to avert this problem, since all the subjects were exposed to the same severe trauma at the same time," said Dr. Goenjian.

To examine this potential link, the researchers recruited 200 participants from 12 families from Gumri, Armenia, who were exposed to the massive Spitak earthquake that claimed the lives of 17,000 people and destroyed more than half the city.

An earthquake-related profile was obtained for each participant that included information on objective experiences during the earthquake, including destruction of residence, deaths of relatives, seeing dead bodies, being injured, or witnessing the injury of another person.

Study subjects were also evaluated with respect to their subjective experiences, which included questions about fear of the earthquake, fear of getting hurt or dying, and fear that someone else would be badly hurt or die. PTSD, anxiety, and depressive symptoms were also assessed.

Disorders Share a Common Link

Unadjusted analyses showed covariates that were significantly associated with severity of PTSD and symptoms included female sex, witnessing death during the earthquake, and pre-earthquake exposure to traumatic experiences.

Covariates that were significantly associated with severity of depressive symptoms included female sex, older age, pre-earthquake traumatic experiences, and death of a family member.

Unadjusted analysis showed heritability of PTSD symptoms was 57%. However, after adjustment for age, sex, and multiple environmental risk factors, the investigators found heritability of PTSD symptoms was still substantial, at 41%.

"This estimate indicates that the proportion of the variation of PTSD symptoms among these participants,because of genetic factors, was 41%, and the rest of the variation is attributable to nongenetic factors," the authors write.

The investigators also note that the high heritability rates for anxiety (61%) and depressive symptoms (66%) in adjusted analyses extend earlier findings for these phenotypes.

In addition to showing that the genetic makeup of some individuals makes them more vulnerable to PTSD, anxiety, and depression, the researchers note the study also indicates that a "large portion of genetic vulnerabilities between the 3 phenotypes are shared and that these genetic factors may be a more important cause of comorbidity than environmental factors."

The study's findings also suggest that PTSD, anxiety, and depression belong to the same diagnostic spectrum of disorders. Finally, say the authors, the results have deepened the understanding of the biology of these disorders and will help in the identification of specific genes involved.

The authors report no conflicts of interest.

Psychiatr Genet. 2008;18:261-266. Abstract

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