When I was a very young school girl, I still remember very well, my Dad used to tell me to bear the pain out and not to scream and cry whenever I hurt myself and was in severe pain. I never ever saw my dad uttering even a simple 'bah' - even when his entire toe nail came out when he hit his foot on the steps of our house. And I screamed on his behalf when I saw this happening to him making him laugh!
I always wanted to be like my dad but could never figure out how that could be done when the pain was so severe for me and made me scream. I always wondered how my dad managed his pain. He was a hero to me then.
But now I know why my dad could bear the pain so well while I cannot. Now my dad is not there to tell him I am not at fault and other things made me scream! Dad, where ever you are, are you listening? This is what I want to tell you:

According to new research results, Pain threshold genes are amplified by lifestyle. Environmental factors might retune your genes to make you more sensitive to pain! Stressful life events such as diet, smoking, drinking and exposure to pollution all have effects on your genes, but we didn't know if they specifically affected pain genes. Now, a study of identical twins suggests they do. It seems that epigenetic changes – environmentally triggered chemical alterations that affect how active your genes are – can dial your pain threshold up or down. This implies that tweaks of this kind, such as the addition of one or more methyl groups to a gene, may account for some differences in how our senses operate.

Tim Spector of King's College London and his colleagues assessed the ability of hundreds of pairs of twins to withstand the heat of a laser on their skin, a standard pain test. They selected 25 pairs who showed the greatest difference in the highest temperature they could bear. Since identical twins have the same genes, any variation in pain sensitivity can be attributed to epigenetic differences.

The researchers screened the twins' DNA for differences in methylation levels across 10 million gene regions. They found a significant difference in nine genes, most of which then turned out to have been previously implicated in pain sensitivity in animal experiments.

The greatest difference was seen with the TrypA1 promoter gene, which governs the activity of an ion channel on the surface of nerve cells that detect pain. "It's like a thermostat, dictating how we perceive heat and turn that into pain," says Spector. An increase in methylation of around 10 per cent in TrypA1 equated roughly to feeling pain at 2 degrees lower (Ref 1)

The results were corroborated in 50 unrelated individuals: those that had the highest levels of methylation on those nine genes were the most sensitive to pain, and vice versa.

Identification of epigenetically altered pain genes opens up ways to screen people for which painkiller might work best, and potentially identify new drugs, says Spector.

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Scientists have also found that  mutations in a gene functions like an on-off switch for agony (3). 

The gene in question is SCN9A, which is responsible for producing a pain-related protein called Nav1.7. In patients who feel nothing, SCN9A is pretty much broken. In those who feel searing random pain, the gene is cranking out far too much Nav1.7.

That discovery raises an obvious question: Can blocking Nav1.7 provide relief for many types of pain—and someday, perhaps, replace dangerous opioid therapies and anti-inflammatories like ibuprofen or with opioids, which bring serious side effects and the potential for abuse?

A pill based on this knowledge tested by Pfizer did well in patients with inherited erythromelalgia, but had little effect on dental pain. A later study testing the same pill on nerve pain related to diabetes was similarly disappointing, and Pfizer quietly shelved the effort last year.

So although the science has been so fascinating, the drug discovery has been challenging. but scientists are optimistic. It’s just a matter of finding the right way to approach the problem.

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Dad, although I inherited half of my genes from you, epigenetic factors might have changed my pain threshold. I know now you want me to change my lifestyle so that I too can increase my pain threshold. Well, I already have a good lifestyle. I don't smoke, drink, or do drugs. I eat very healthy food ( Ref 2). But pollution and stress are what I have no control on. But still I will try to increase my tolerance to pain! Promise!

References:
1. http://www.nature.com/ncomms/2014/140204/ncomms3978/full/ncomms3978...

2. http://kkartlab.in/group/some-science/forum/topics/the-road-to-a-he...

3. https://www.statnews.com/2016/07/05/pain-drug-opioid-alternative/

(Read the full paper on pain tolerance by clicking on the first link)

Q: Is there a difference between pain threshold and pain tolerance?

Krishna: Yes! Pain ‘threshold’ or pain ‘tolerance’? Because they’re different things.

Your pain threshold is the point where a sensation (temperature, pressure, the spiciness of food and so on) crosses a line, going from being innocuous to causing you to experience actual pain. The extent to which you can withstand and endure the pain you’re experiencing, while continuing to function, is your pain tolerance.

Pain thresholds and tolerance are things where age, sex and other factors have a significant impact. For instance, it’s regularly assumed that women have much higher pain tolerance than men because they can experience childbirth. But research shows that, while women often report experiencing more pain than men, their pain tolerance increases dramatically during pregnancy and labour, due to the many significant physiological and hormonal changes they undergo as a result of the process.

Overall, someone’s ability to experience, process and endure pain is determined by many, constantly shifting, factors. It’s hard to say how many of these apply to us. But there’s no guarantee that they always will.