So, what if you had a study where identical twins were subject to difference occupations and followed over time to see if there was any difference in the development of disk degeneration? I think everyone would agree that would be a fascinating study. If we had just a study, maybe we would have enough data to answer the question of genetics over environment. Does increased occupational stress increase disk degeneration? Does genetics have a role in the development of disk degeneration?
Well, in the Spine Journal of January 2009, Battie, et al reported on a 1991 Twin Spine Study about a multinational research project that followed twins from Canada, Finland and the United States. The study gather data regarding disk degeneration and relationships with occupational exposure, smoking, driving and whole body vibrational exposure, anthropomorphic characteristics, inheretability and the potential genetic nature of degeneration.
The study indicated a significant genetic effect associated with the development of disc degeneration. For many of the twins, there was a significant difference in occupational and recreational spinal loads. Identical twins had different interests, and had jobs with significant physical demands. Yet, the development of disc degeneration was similar in these identical twins.
The study concluded that the conventional wisdom of assuming occupational and physical loading causes disc degeneration was not correct. The identical twins developed disc degeneration in similar manners despite differences in occupation and recreational exposures. The study indicates that genetics determine the development of disc degeneration rather than “wear and tear” of life or occupational exposure.
This article was a followup to a 5 year twin study published in 2006. In that study, it concluded that in identical twins, only 2%-10% of the degeneration can be attributable to occupational and physical loading. The vast majority of disc degeneration is secondary to genetics and similar environmental exposures.
Currently, there is a significant amount of research being devoted to identifying the genetic markers associated with accelerated disc degeneration, and other musculoskeletal manifestations. In clinic practice, at times, we see families that have serial generations with similar findings. Often times, we are not sure if the clinical complaints are completely environmental, familial pattern of behavior, or genetics. In the future, we may have genetic testing that may enlighten us to the cause of these familial patterns.
While research continues, these studies do indicate lumbar disc degeneration does have a significant genetic component. This information may inflame the debate on the theories of occupational and traumatically induced disc degeneration.
- Battié MC, Videman T, Kaprio J, Gibbons LE, Gill K, Manninen H, Saarela J, Peltonen L. The Twin Spine Study: contributions to a changing view of disc degeneration. Spine J. 2009 Jan-Feb;9(1):47-59. PubMed PMID: 19111259