A study of gene-environment interactions

This 2018 Hungary/UK study used Bayesian analysis to better understand gene-environment interactions that produce depression:

“Most genetic studies do not consider the effect of stressors which may be one reason for the lack of replicable results in candidate gene studies, GWAS [genome-wide association studies] and between human studies and animal models..Animal models of depression usually imply environmental factors, such as chronic unpredictable stress or learned helplessness.

Relevance of functional polymorphisms in seven candidate genes previously implicated in animal and human studies on a depression-related phenotype given various recent stress exposure levels was assessed with Bayesian relevance analysis in 1682 subjects.

Our data support the strong causative role of the environment modified by genetic factors, similar to animal models.”

From the Methods and Materials section:

“In order to identify recent negative life events (RLE) we used the List of Threatening Experiences questionnaire which queried problems related to illnesses/injuries, financial difficulties, problems related to intimate relationships, and social network occurring in the last year. Based on corresponding items the number of RLEs was counted for each subject, and categorized (low = 0–1, moderate = 2, high = 3/more).”

One item from the findings, and two from the cited references were:

“5-HTTLPR [serotonin transporter], the most extensively investigated polymorphism with respect to interaction with life events, showed only very low relevance.

Compared to heritability which accounts for 37–42% in the variance in general population samples, influence of environmental effects is estimated at 63% in depression.

Etiologically relevant distal and proximal stressors are relatively common, and while frequency of severe life events is estimated to be one in every 3–4 years, depression is triggered in only about one fifth of those with acute stress exposure.”

The methods of this study bypassed problems with GWAS and provided evidence for the lasting effects of “Etiologically relevant distal..stressors.” This was another way of saying that traumatic experiences beginning from the earliest parts of our lives still affect our biology and behavior.

As mentioned in Changing an individual’s future behavior even before they’re born, GWAS:

“Focuses on the average effect of alternative alleles averaged in a population.”

What this methodology often missed was:

“When phenotypic variation results from alleles that modify phenotypic variance rather than the mean, this link between genotype and phenotype will not be detected.”

The problems found in GWAS may also be found in epigenome-wide association studies. Researchers conducting DNA methylation analyses in particular may benefit from changing their approach if what they’re doing follows the GWAS paradigm.

Using twins to estimate the extent of epigenetic effects summarized three studies’ methods that showed:

“The epigenetic effects of each of our unique experiences of our non-shared environment predominately determine our individual physiology.”

This study’s approach should be considered, given the almost 2:1 relative impacts of environmental over genetic factors in influencing our biology and behavior. It’s especially indicated when human studies don’t replicate animal studies’ findings from strictly controlled experimental environments.

It wasn’t the study’s purpose to evaluate effective treatments for depression. Yet the abstract ended with:

“Galanin-2 receptor, BDNF and X-type purin-7 receptor could be drug targets for new antidepressants.”

The researchers were very careful to document the benefits of using a different approach to a problem. I hope that in the future, they will maintain their carefulness and independence in their approach to solutions, and not be influenced by:

“Consultancy, speaking engagements and research for Bristol-Myers Squibb, AstraZeneca, Eli Lilly, Schering Plough, Janssen-Cilag and Servier..share options in P1vital..consultancy fees from Alkermes, Lundbeck-Otsuka Ltd., Janssen-Cilag Ltd and fees for speaking from Lundbeck.”

https://www.nature.com/articles/s41598-018-22221-z “Significance of risk polymorphisms for depression depends on stress exposure”


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s