The upright body position compresses on the spine and discs. I had several bulging discs in my mid 20's. Through simple strengthening exercises and diligent assessment of body posture when awake and asleep (don't ask how that was done) I was able to overcome it after a year. Had to deal with relapses for 20 years, but now there seems to be no pressure on the nerves. Certain seating positions are terrible for me, and others are not. I do find a traditional road bike with the curly bars helps my back significantly, but also find the recumbent is OK as long as the lower back is properly supported.
Every injury is particular to the body in which it occurred. Get a second and third opinion and see a PT that is up to date with new methods for this type of injury. If it is a genetic disorder, you're stuck with it.