Chronic Pain’s Paralell Universe: Congenital Analgesia

Being unable to feel pain sounds enticing, but people with congenital analgesia frequently bite their tongues, break bones or burn themselves without being aware of it, sometimes leading to severe damage-or early death. According to some reports, people who have this condition rarely live past the age of 30 because of the physical toll a life without pain actually takes on the body.
I often write about chronic pain, but we should all stop to think of life if each of us had to live it chronically without pain. The physical damage mentioned in the first sentence is troubling enough. But imagine the potential for psychological injury in those unable to feel pain: Really, how will the individual suffering from congenital analgesia ever be able to "feel your pain"? Those with congenital analgesia may truly believe that you just need to "suck it up" the next time you smash your thumb with the hammer. How many friends and loved ones want to associate with that sort of person? No sympathy, and he does not even feel the pain of a well executed bitch-slap!
The diagnostic criteria generally agreed upon for this disorder include a generalized indifference to pain dating from birth; no impairment of other sensory modalities; normal intelligence; normal deep tendon reflexes; no visceral pain perception; normal skin biopsy; no diminution of myelinated or un-myelinated nerve fibres in sural nerve biopsy; normal motor and sensory nerve conduction velocities; and normal karyotype.
Interestingly, those with congenital analgesia can still feel sensations such as normal body-to-body contact, which means that the brain can receive some information filtered through the nervous system: Perception of passive movement, joint position, and vibration is normal, as are tactile thresholds and light touch perception. Likewise, the ability to distinguish sharp and dull stimuli and detect differences in temperature also appears to remain intact. Reflexes are maintained. However, when it comes to extreme temperature changes, or any bodily damage that signals the body to react in an emergency fashion, the body simply doesn't respond.
It is known that the inability to feel pain is due to a particular defective gene (SCN9A), which codes for a particular type of sodium channel protein. These sodium channels are essential for pain nerves to be able to send messages from the periphery of the body to the brain. Any slight mutation of this gene makes it completely non-functional, disabling the brain's ability to interpret input pertinent to health.
Curiously, the SCN9A gene is also involved in the loss of sense of smell, according to an article published in the journal "Nature" last year. The researchers tested three people in their 30s with congenital analgesia and found they were unable to smell at all (a condition known as anosmia). Interestingly, none of the subjects had been aware that they could not smell. The researchers hypothesized that sodium channels could be important in smell detection too.
In fact, the researchers demonstrated that the olfactory sensory nerves that relay smell information in both humans and mice did indeed contain the sodium channels. Next, they created a genetically-altered strain of mice that lacked the sodium channels and were unable to smell. These mice were compared with normal mice, carefully recording the electrical activity of single nerve cells as the animals were exposed to smells. Surprisingly, the nerve cells responded normally to smell, but the signals were not reaching further into the brain. The sodium channels appear to be essential for triggering the release of neurotransmitter, which is essential for transmission of information from one nerve cell to the next.
Thinking ahead, smell (or lack of it) may be a side-effect we have to consider when we take a drug for severe pain in years to come, as several pharmaceutical companies are racing to develop pain relief drugs targeting these particular sodium channels.
On the plus side, two of the individuals studied in the "Nature" paper had given birth with completely pain-free labor. PT blogger and author Jena Pincott in her latest book "Do Chocolate Lovers Have Sweeter Babies?" reflects on "a purpose to painful birth." She discusses the claim that, for many, childbirth is "ecstatic pain, like running a marathon," and afterwards endorphins will work their magic, leaving in their wake a memory of achievement. While the pain of labor may be, as Pincott writes, "Eve's burden," it also may be a reminder-albeit modulated via those endorphins-of the great work of art a new life is, deserving of all the care a mother and a society can give. And I cannot help wondering whether those congenital analgesia patients with their pain-free labor will feel, or even intellectually experience, that sense of wonder that seems to accompany all new life.
Or will they just turn to their respective screaming roommates in Labor and Delivery, and in between cell phone conversations calmly suggest they just suck it up?