A 'NORMAL' PAIN RESPONSE: GENETICS
Wherever there is a variation in a species or between species, it is obvious that genetics should be investigated as a possible source. One of the puzzles of pain in humans is that severe nerve injury can produce long-lasting intractable pain of great ferocity. However, an additional puzzle is that the prolonged pain occurs only in a fraction of those with apparently similar injuries. In military amputees, all have obvious serious problems but only 10 to 20 per cent have the devastating pains caused by injury to their large nerves.
At the Hebrew University in Jerusalem, a twenty-year study has been carried out on rats who begin to show possible signs of pain two weeks after their sciatic nerve had been cut. The animals were not allowed to suffer, and were killed as soon as they showed the first signs. It was noted that some strains of rat never suffered this condition. By selection, cross-breeding and DNA analysis, a single gene responsible for the condition has now been located. The next stage, which is being vigorously pursued in universities and pharmaceutical companies, is to identify the responsible protein. It is clear that a very specific treatment might emerge that would control the pains caused by nerve damage.
Some strains of mice have high thresholds to the ordinary pain tests. Some painful diseases clearly have a genetic origin. Sickle-cell anaemia, which is common in people of African origin, is a genetic disease that provides resistance to malaria in those with one gene but produces a disease with acutely painful crises in the minority who have two of the genes.
Although genetics plays some role in every aspect of humans, there is no evidence that it plays a large part in common pains. The main reason for this definite statement is that pain varies in the same individual, depending on the circumstances. This variation cannot be entirely due to genes as such because it is learned during the individual's lifetime.
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Pain Relief