Can PTSD Be Inherited?

What is PTSD: symptoms and diagnosis

Post-traumatic stress disorder (PTSD) is a disorder prompted by exposure to a traumatic event. A traumatic event can include abuse, war, death, torture, sexual violence, or neglect.

People can directly experience these events, witness them, or be repeatedly informed of them (e.g., first responders or police).

PTSD is characterized by four categories of symptoms: intrusion (sometimes referred to as re-experiencing), avoidance, arousal/reactivity, and mood changes. Such symptoms significantly reduce an individual's quality of life and include:

Intrusion

• Recurrent distressing dreams which are related to the event

• Recurrent, involuntary, and intrusive memories of the event

• Dissociative reactions, such as flashbacks where you may feel as if the traumatic event is reoccurring

• Intense distress at exposure to cues that resemble the previous traumatic event 

Avoidance

• Avoiding triggers/stimuli related to the event, e.g., people, places, or activities

• Avoiding discussions or thoughts about memories of the event

Arousal and reactivity

• Irritability

• Increased startle response

• Hypervigilance

• Impulsivity and reckless behavior

• Sleep disturbances

• Difficulties with concentration 

Negative cognitions and mood

• Persistent negative affect (feeling low or experiencing emotions such as anger, guilt, or shame)

• Memory loss surrounding the event

• Negative feelings about yourself and those around you

• Distorted cognitions around the traumatic event which lead you to blame yourself

• Reduced interest in previously pleasurable activities

• Shame, blame, guilt, or fear

• Isolation from others

• Inability to feel positive emotions such as happiness 

To be diagnosed with PTSD, the person must experience at least one intrusion symptom, at least one avoidance symptom, at least two arousal/reactivity symptoms, and at least two cognition/mood symptoms.

These symptoms must be prompted by direct or indirect exposure to at least one traumatic event and last for at least one month. These issues must not be caused by a drug or better explained by another condition.

It’s important to note that the above diagnostic criteria apply to individuals over the age of six (DSM-5). Additional special criteria must be met for children six and under.

Risk factors of PTSD

Most people will experience at least one traumatic event in their life, whether that be the death of a loved one, witnessing violence toward others, or a natural disaster.

However, not all people will develop PTSD.

The lifetime prevalence of PTSD is estimated to be just under 7% in US adults over 18.¹ So why are some people more likely to develop PTSD than others?

As with any psychological or physiological disorder, certain factors increase the risk of developing it. In the case of PTSD, many factors may increase its likelihood of occurring, including:

• Low socioeconomic status

• Increased severity of trauma

• Lack of social support

• Abuse in childhood

• Being in a minority race

• Psychiatric history

While these factors may not cause PTSD, they may increase one's likelihood of developing it. In saying this, someone with these risk factors may experience a traumatic event and not develop PTSD.

PTSD and genetics: Can PTSD be inherited?

In addition to the risk factors mentioned above, many experts have suggested that genetics play a significant role in PTSD development.

One report suggests that nearly a third of the variance in PTSD cases can be explained by genetics.² This has been demonstrated by twin studies in which monozygotic (genetically identical) twins were more likely to have PTSD than dizygotic (genetically different) twins after exposure to traumatic events.

Researchers have spent significant time researching any predisposing factors to PTSD. A 2012 study used twins to determine if a smaller hippocampus was caused by the diagnosis of PTSD or was perhaps an underlying risk factor for developing PTSD.³ In this study, twins with smaller hippocampi were more likely to have PTSD than twins with large hippocampi. 

This factor may be heritable and increase an individual's risk for PTSD. In saying this, the authors recognize a pre-existing shared environment may influence hippocampal size. So further research is required before drawing any conclusions.

A large gene-wide association study has also demonstrated a shared genetic risk between PTSD and other psychiatric conditions.⁴ Specifically, this study demonstrated a significant overlap of genetic risk factors between PTSD and schizophrenia and slight evidence of overlap between PTSD, bipolar disorder, and major depressive disorder.

However, the authors acknowledge that further studies with better power need to be undertaken in this area.

An additional study of over 30,000 people with PTSD and 170,000 controls (i.e., people without PTSD) also found evidence of heritability and a genetic relationship with other psychiatric conditions.⁵

A note on generational trauma

While generational trauma is not specifically inherited through genetics, it can be passed down through families. Many experts look at how the traumatic experiences of our parents and grandparents may be passed down to us.

For example, research in the late 90s suggested that Holocaust survivors’ children had a much higher risk of developing PTSD (alongside other psychiatric disorders) than controls (e.g., children whose parents did not experience the Holocaust).⁶

Similar results were found for descendants of Armenian refugees, who reported at least subclinical presentations of PTSD for most of their adult life.⁷ This result was worse in women.

This sort of generational trauma may be passed on by many mechanisms, including children identifying with their parents suffering at similar ages or the responsibility children take on to compensate for the suffering of their parents.

It may also be passed on more indirectly by differences in parenting prompted by trauma or differences in communication styles.

The lowdown

PTSD is a well-recognized disorder caused by exposure to a traumatic event. While many people will be exposed to a traumatic event in their lifetime, not all will develop PTSD. The likelihood of developing this disorder seems to be increased by genetic factors. Research into the specific genetics of PTSD is still in its early stages, and new evidence relating to this will likely be published in the coming years.

PTSD may be transmitted generationally without an associated genetic influence. Grandparents who have experienced extreme trauma can pass it on to their children, who may even pass it on to their own children.