There's no known genetic cause of DDD. Tobacco use has a known negative effect on the disc. You didn't mention your age. Degenerative disc disease (DDD) often occurs gradually over time with the aging process.
As we age, the water and protein content of the disc changes. This change results in a weaker, thinner disc. Wear and tear makes the problem worse. The gradual deterioration of the disc between the vertebrae is called degenerative disc disease. This condition is seen on an X-ray or MRI as a narrowing of the normal disc space.
Degeneration of the disc tissue makes the disc at risk for herniation. The disc doesn't have much of a blood supply. Once it's injured, it can't repair itself easily. A small tear in the outer covering of the disc can lead to major problems.
Any of these changes can occur in adults, even those who've never been active in sports or heavy lifting.