We are truly intricate and complex — a biological system — and genetic variants often don’t have a huge impact on their own. Instead, the impact comes in the combination of gene variants or the interaction of a variant with the environment (toxins, stress, sleep, diet, pathogens, etc.).
A brain imaging study recently showed that the combination of a BDNF genetic variant plus a serotonin receptor variant literally changes the brain. Instead of just looking at a single genetic variant, this article digs into how the combination of these two variants interact to increase the risk of depression, anxiety, and bipolar disorder.
Let’s get into some background science and then go into how BDNF and serotonin work together.
Background on BDNF:
You may think you only have the brain cells you were born with. Perhaps your parents told you this when you were a teenager to prevent you from drinking :-)
However, research now shows that you can actually add brain cells to certain areas of your brain, especially in the hippocampus. You can also increase the connections between the neurons, increasing the brain’s plasticity.
BDNF is the key to producing more neurons.
BDNF stands for brain-derived neurotrophic factor. It is a type of protein called neurotrophin. BDNF works in several ways:
- BDNF encourages new neuronal growth from stem cells
- it protects neurons from injury and cell death
- it improves neuronal function (important in learning and mood)
To improve the way the neurons function, BDNF binds to receptors that are located in the synapses between neurons. BDNF potentiates or increases the signal from one neuron to the next.
In addition to being found in the brain, BDNF is also found in the peripheral nervous system – helping muscle nerves to function well. This connection with muscles is one way that exercise increases BDNF.
Studies on BDNF show:
- Chronic stress causes a decrease in BDNF.[ref]
- Low BDNF is linked to Alzheimer’s disease[ref] and Parkinson’s[ref][ref]
- People with depression usually have lower levels of BDNF.[ref][ref][ref]
- Mothers with postpartum or during-pregnancy depression have low BDNF[ref], and the elderly with depression also have low BDNF.[ref]
- Low BDNF is linked to obesity.[ref]
BDNF doesn’t necessarily act alone in causing diseases. It often interacts with neurotransmitters or cytokines. For example, a recent study found that in people with schizophrenia, lower BDNF levels correlated with higher IL-2 (interleukin-2) levels. IL-2 is an inflammatory cytokine that is part of the immune system.[ref]
BDNF Genotype Report:
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There is one well-studied genetic variant in the BDNF gene. (Literally, thousands of studies on it…) It is knowns as the Val66Met (rs6265) variant.
Check your genetic data for rs6265 (23andMe v4, v5; AncestryDNA):
- T/T: decreased BDNF[ref] referred to in studies as Met/Met
- C/T: somewhat decreased BDNF, referred to as Val/Met
- C/C: typical BDNF, referred to as Val/Val
Members: Your genotype for rs6265 is —.
The T allele (decreased BDNF in the brain) is linked in studies to:
- decreased hippocampal volume if exposed to early-life stress[ref]
- altered learning and recall[ref][ref]
- more likely to be overweight[ref]
- increased anxiety and altered response to antidepressants[ref]
- less likely to respond to citalopram and escitalopram (antidepressants).[ref] Note that this doesn’t mean that those antidepressants absolutely won’t work, just that a larger proportion of people carrying the T allele didn’t respond compared with people carrying the C/C genotype
Not all studies show that the rs6265 T allele affects depression or anxiety.[ref] There are a lot of conflicting studies that muddy the water… It isn’t as simple as T-allele = bad brain.
First, lifestyle factors increase or decrease BDNF (more on these in the Lifehacks section below).
Second, other genetic variants are important. Such as the serotonin gene variant below.
Third, the T-allele is also linked with positive traits, such as being more resistant to social defeat.[ref] The song lyrics “I get knocked down, but I get up again, You are never gonna keep me down…” may apply to people with the T-allele.
Background on Serotonin:
Serotonin is often thought of as a happy neurotransmitter and is linked to feelings of well-being. (Serotonin does many things in the body and is not just in the brain. But here, I’m just focusing on its role as a brain neurotransmitter.)
Tons of research exists showing links between serotonin and depression. To sum up the research: depression and serotonin seem linked somehow. Yep, pretty wishy-washy for decades of research. Again, it doesn’t seem like there are simple answers here, such as simply increasing serotonin to cure depression.
Serotonin works as a neurotransmitter to transmit signals in a variety of neurons in the brain. It is released by a neuron into the synapses and then binds to the next neuron causing the signal to be transmitted.
Whole books could be (and have been) written on serotonin and depression. Instead of getting too deep into the weeds here, I’m going to dive into one specific serotonin receptor…
HTR1A Serotonin Receptor:
The serotonin receptor known as 5-HT1A is coded for by the HTR1A gene. Here, I’m just going to call it the serotonin 1A receptor. (There are a bunch of different serotonin receptors that do different things in the body.)
Basically, one neuron releases serotonin into the space (synapse) next to the beginning of the next neuron. Then serotonin binds to receptors on the next neuron, triggering a reaction that sends the signal along. The receptors are specific to serotonin — in this case, we’re talking about the serotonin 1A receptor.
BDNF is also active in the brain and potentiates the release of serotonin.[ref] It gives it a boost. Like adding nitrous to your car. OK, maybe not that big of a boost.
Research shows the serotonin 1A receptor variant has links to depression. A new study now points to an interaction between the serotonin receptor variant and the BDNF variant when it comes to depression.
Check your genetic data for rs6295 (23andMe v4, v5):
- C/C: typical risk of depression*
- C/G: linked with an increased risk of depression
- G/G: linked with an increased risk of depression in most (but not all) studies[ref]
Members: Your genotype for rs6295 is —.
* Given in plus orientation to match 23andMe data
A meta-analysis of several studies on rs6295 found links to an increased risk of depression in Asian populations.[ref] Not all studies agree, of course.[ref]
Combination of BDNF and serotonin variants:
While each of these variants has a link to increases in mood disorders on their own, not all studies agree, and the increase in risk isn’t all that large. Kind of like something is missing from the picture when you look at each gene separately.
The key to the increased risk of depression and anxiety disorders due to the serotonin 1a receptor and BDNF variants may be the combination of the risk alleles.
A recent study looked at the combined effects of carrying both the serotonin 1a receptor (rs6295) variant and the BDNF rs6265 variant.[ref]
The study used PET scan imaging of the brains of people with affective disorders (depression, bipolar, anxiety disorders) and at least three copies of the variant alleles (combos of rs6295 G-alleles and rs6265 T-alleles). Brain imaging showed that the risk variants altered the serotonin 1a receptor binding in ways associated with affective disorders.
There are several different ways that you can increase your BDNF levels:
Lifestyle changes for improving BDNF levels:
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Related Articles and Topics:
Bipolar disorder and the circadian clock genes:
New research shows that depression and bipolar disorder are linked to changes or disruptions in circadian genes. Some people carry genetic variants in the circadian genes that make them more susceptible to circadian disruption.
Tryptophan is an amino acid that the body uses to make serotonin and melatonin. Genetic variants can impact the amount of tryptophan that is used for serotonin. This can influence mood, sleep, neurotransmitters, and immune response.
Circadian Rhythm Genes: Mood Disorders
Circadian rhythm disruption can drive mood disorders. Learn more about the genes involved and the ways to normalize your circadian rhythm.
Anxiety: Genetics and personalized solutions
This article covers genetic variants related to anxiety disorders. Genetic variants combine with environmental factors (nutrition, sleep, relationships, etc.) when it comes to anxiety. There is not a single “anxiety gene”. Instead, there are many genes that can be involved – and many genetic pathways to target for solutions.
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