If your mother or father had PTSD, you have an increased risk of developing the problem. But that doesn’t prove that it’s genetic. Family life with a stressed out parent carries it’s own morbidity. In a study of the children of Holocaust survivors, the mom’s trauma history was significantly more important than the dad’s, suggesting that the quality of mothering might be more relevant than genes.
The long-term effects of early deprivation have been well documented for over forty years. We now know that babies raised by depressed, absent, or stressed mothers have changes not only in behavior but also in their neurochemistry.
In these kids the hypothalamus to pituitary to adrenal gland (HPA) pathway, when compared to normal kids, shows changes in the timing and amounts of cortisol released during times of stress.
But these changes can take different forms. They can increase or decrease the person’s odds of developing anxiety, depression, or PTSD. It looks as if a little deprivation can actually build up your resilience, but a lot leaves your nervous system over-sensitive.
More recent research shows that early stress also changes which genes we use. Stress can turn our genes on and off by adding a methyl group to the nucleotide cysteine. This epigenetic change is permanent. It can even be passed down to future generations, much like a real mutation.
Scientists are trying to develop medications that remove methyl groups and free the genes, but whether these will prove both helpful and safe is still untested and unknown.
With our new knowledge about the human genome, there’s been a rush of studies linking genes to disorders. Several gene mutations are more frequently found in people with PTSD, suggesting that those mutations may increase the risk. More studies are underway on genes that are known to increase anxiety or depressive illness, particularly those that effect the neurotransmitter serotonin. But if PTSD acts like other mental problems, we’ll find many mutations that can weaken our resistance and no single gene that is the cause.
One study released last year in JAMA Psychiatry by collaborators at University of Michigan and Columbia University School of Public Heath described a specific mutation of the ADRB2 gene, which when combined with childhood adversity, significantly increased the risk of PTSD. Two groups were studied, a group of combat soldiers in the National Guard, and a group of black, inner city women. All the folks with this particular mutation AND aversive childhood experience, were more likely to develop PTSD as an adult. However, the increased risk for people with both the mutation and childhood adversity was only a fraction of the total risk—like being near to a disaster instead of farther off.
Twin studies are a cornerstone of genetic research since identical twins share the same genetics but may live very different lives. Twin studies done in Vietnam showed that 30% of the risk for PTSD could be traced back to genetics.
In one twin study the researchers measured hippocampal size, since previous research found smaller hippocampal volumes in MRIs done on veterans with PTSD. This research studied twin pairs where only one twin had PTSD symptoms, but MRIs found no difference between the two twins’ hippocampal volumes. This argues that a smaller hippocampus is caused by genetics and not stress. The researchers suggest that a smaller hippocampus might put you at greater risk of PTSD, which would explain this finding among PTSD diagnosed veterans.
Some people have a higher risk of PTSD symptoms due to early trauma, epigenetics, and genetics, but these factors explain only 30% of the total risk and pale beside overwhelming trauma. We don’t yet know enough to effectively screen people so we can protect those who will suffer most. The length of time you’re exposed and severity of trauma are still the most accurate predictors of your risk.