Mutant Gene May Cause Back Pain     Research workers at Hahnemann University Medical Center in Philadelphia have identified a mutant gene that may be responsible for some cases of sciatica, a sometimes severe and chronic type of back and leg pain. This finding could help doctors identify other people at risk for sciatica.     Back pain has been one of the most common problems affecting patients throughout the world, but still is poorly understood as to why it occurs. Most adults will be affected at some point during their lives.     Sciatica is most often caused by a ruptured disc, which occurs when the material within the central aspect of the disc protrudes and causes pressure on a nerve root usually in the lower part of the back.     Scientists believe that smoking and occupational factors put people at higher risk for sciatica, but this gene may be another factor. If a person were to know that he carried this particular gene, he or she could be properly advised regarding activities and occupations.     The mutated gene alters an important protein inside the disc preventing it from forming into the correct shape. It changes the disc material and makes it less capable of absorbing shocks placed on the spine over time.     If genetic factors are found to underlie a substantial percentage of cases of sciatica it would drastically change the way we think about the disease and about risk factors and occupational causes. It might even lead to prevention.