Background
Some may not know that before an individual can enter chiropractic college/university, they must first attend undergraduate college. The vast majority of modern chiropractors have undergraduate degrees, primarily in the sciences (science is a requirement for chiropractic college acceptance). In fact, many chiropractic colleges/universities also have programs to educate and grant accredited undergraduate science degrees.
After undergraduate college, chiropractic college/university is an additional 4-5 year program. After completing the program and having passed all national and state board examinations, the graduate is awarded the degree of DC, which stands for Doctor of Chiropractic. Yet, while being educated, instructors often note that the DC degree actually stands for “Doctor of Chronic.” This is because chiropractors thrive on chronic pain patients, especially chronic spinal pain patients.
There is no doubt that chiropractic and spinal manipulation works well in the treating of chronic spinal pain problems, including in patients who have failed to achieve an acceptable clinical response to other more traditional approaches to their problems (1, 2, 3, 4, 5, 6, 7, 8, 9). There are a number of published plausible explanations for these outcomes, including:
A new plausible explanation is evolving, and this article explores it: Genetics.
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Questions
Why do two individuals of similar physique, age, fitness, etc., injured in the same accident, have completely different post-event pain presentations?
Why do two individuals of similar physique, age, fitness, etc., after receiving similar injury (let’s say a sprained ankle or a whiplash neck injury), have very different pain recovery times? (One may recover in days to weeks, the other takes months or even years).
Are there scientific, physiological explanations that account for individual variation in pain recovery rates?
Why do so many chronic pain patients gravitate towards chiropractic? And what are some of the evolving explanations as to why chiropractic helps such individuals?
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Biology 101
Our structure, hormones, neurotransmitters, enzymes, and more, are made up of proteins. All told, the human body uses about 22,000 proteins.
Proteins are derived from building blocks called amino acids.
The amino acids that are used to build our proteins come from our diet. (Some of these amino acids are essential, meaning that they must come from our diet; others can be manufactured in our body from other molecules, primarily other amino acids).
When humans consume protein in the diet, our digestive system breaks the protein down into its individual amino acids.
These dietary amino acids are reassembled into the approximate 22,000 proteins that the human body requires to run efficiently.
The reassembly of these amino acids into the functional proteins of life is the job of the human genome, our genetic material. Our genes are essentially a protein assembly factory.
Stated differently, approximately 22,000 human genes code for (assemble) approximately 22,000 proteins.
Our genetic material is often referred to as DNA, an abbreviation for deoxyribonucleic acid. A component of this deoxyribonucleic acid is the nucleotide bases.
Even though there are only four different nucleotide bases that make up the human genome, their total number is approximately 3 billion. Essentially, approximately 3 billion nucleotide bases code for (assembling) approximately 22,000 proteins. (Not all nucleotide bases code for protein, some is quiescent, or non-coding, or “junk [probably not]” or not yet understood).
All of this genetic material (nucleotide bases) is packed into 23 pairs of chromosomes. Each cell in our body (about 75 trillion of them) has a complete copy of all 23 chromosomes with its approximate 3-billion nucleotide bases. (There are two exceptions. Red blood cells [approximately 25 trillion of them] contain no genetic material. Sex cells have only one copy of the 23 chromosomes, not a pair; the pair is reestablished when the parents conceive a baby).
When assembling a protein, each amino acid building block is assigned to three adjacent nucleotide bases. The three nucleotide bases that are hooked up to one amino acid is call a codon. The section of a chromosome that codes (assembles) a single protein is called a gene. An example of putting it all together:
Damage to the nucleotide bases of the DNA alters the assembly of the proteins of life. This is the rationale for minimizing exposure to ionizing radiation, free radicals, toxic chemicals, etc.
All proteins of life are important. The emphasis of this paper is a special class of proteins called enzymes.
Enzymes are proteins that act to help the body complete metabolic/biochemical processes. Our life is not possible without these enzymes. The biochemistry of life, without enzymes, would require so much heat or so much pressure that either would kill us.
All enzymes are proteins, meaning that we have a gene that codes for (assembles) them. When reading science, one can always identify enzymes because they end in the letters ase.
All episodes of CSI or any other crime television program emphasize there are differences in each of our DNA, or specifically in the nucleotide base sequence of our DNA. These differences account for the differences between people, such as height, eye-skin-hair color, etc. The point of this discussion is that in a similar fashion, each of us has a different expression (assembling) of the genes that code for (assembles) enzymes. One such enzyme has become particularly important in the understanding of the benefits of the chiropractic adjustment in the treatment of chronic pain.
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Physiology
Pain is an electrical signal in the brain. Oversimplified, five structures are involved for the pain electrical signal to reach the brain:
The Receptor
The receptor converts an environmental stress into the electrical signal.
The Primary Afferent Neuron
The primary afferent neuron brings the electrical signal from the receptor to the spinal cord.
The Synapse
The synapse is the gap between the primary afferent neuron and the second order afferent neuron.
The Second Order Afferent Neuron
The second order afferent neuron brings the electrical signal from the synapse to the brain for the perception of pain.
The Brain for the perception of pain
The brain perceives the electrical signal of pain.
Important for this discussion, the threshold and sensitivity of the primary afferent neuron is influenced by a chemical called norepinephrine (noradrenaline). Norepinephrine is produced by post-ganglionic sympathetic neurons. Norepinephrine makes the primary afferent neuron more sensitive, or making more painful, increasing the pain electrical signal to the brain:
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Genetics
Increasingly, individual differences in the intensity, duration and recovery from pain syndromes is being attributed to genetic differences, and specifically to the production of particular enzymes that influence the electrical threshold and transmission of the pain neurons. The genetics of pain is detailed in the 5th edition of the book Wall and Melzack’s Textbook of Pain, 2006 (14). Chapter 9 is titled “The Genetics of Pain.” The summary of this book includes:
“Pain is associated with considerable variability between individuals. Humans exhibit robust differences in their thresholds and tolerances to controlled noxious stimuli, in their analgesic response to drugs, and in their susceptibility to (and severity of) clinical pain syndromes.”
Pain genetics is better understood in the 2014 book by Judy Foreman, titled “A Nation in Pain.” Her pertinent chapter, chapter 3 is also titled “The Genetics of Pain.” (15) Ms. Foreman notes that genetics influence both the susceptibility and sensitivity to pain, which she defines as:
Genetic susceptibility means the likelihood that you’ll get a chronic pain condition.
Genetic sensitivity means how much it hurts if you do have a chronic pain condition.
On this topic, Ms. Foreman states:
“Scientists now think that genes control perhaps 50 percent of susceptibility to chronic pain.”
“Across a number of different kinds of pain, genes seem to be at least half the driver of how much pain you experience.”
In her review of the literature, Ms. Foreman notes that a “favorite gene of pain geneticists is COMT.”
COMT is an enzyme. It’s the abbreviation for:
Catechol-Oxygen-Methyltransferase = Catechol-O-Methyltransferase
In review, note that this enzyme ends in the suffix ase, further establishing that it is a protein, and as such there is a gene that codes for (assembles) it. And all genes express differently person to person. Apparently the individual expression of COMT can significantly alter one’s sensitivity to pain. Ms. Foreman states:
“We all have the COMT gene, but some people have a form of the gene with high activity, and some, the form with low activity.”
“High activity is better! High COMT means low pain and low COMT means high pain.”
“The luckiest 40 percent of Caucasians have the high-activity form and are relatively unsusceptible to pain.” These individuals are only half as likely as others to develop chronic pain syndromes.