Research on Twins and Disc Degeneration
Hi, I'm Dr. John Shim, and I'd like to discuss genetics and back pain. Let's get this out of the way first. None of us can control our genetics. We are born with physical characteristics from both our parents. The more scientists learn the more we realize many things about our health is programmed by our genetics. As we continue to learn we now believe genetics is relevant to conditions such as heart disease, certain types of cancers, and type 1 diabetes. From an athletic perspective, some scientific data suggests there are specific genes that provide potential for more endurance, more muscle power, or more flexibility. But we cannot completely blame our genes for everything or attribute our successes to our genetics. As individuals, we should accept the principle that despite your genetics. You can enhance your health or athletic achievement with hard work, healthy habits, and a positive attitude. Potential does not mean achievement. Predisposition does not mean certainty. So what about your genetics and back pain? There have been several studies following identical twins throughout their lives, and the results have been interesting but not necessarily conclusive. Nevertheless, we should explore some of the results. A study of twins was published in The Spine Journal in 2009. To summarize, scientists studied twin males since 1991. Twins were followed for MRI findings of disc degeneration. Twins that were studied, include pairs, with one smoking cigarettes, while the other was not a smoker. Another twin group included pairs that perform significantly different physically demanding careers. Heavy labor versus moderate or light labor. In this study, the smoking twin did show more disk degeneration. Surprisingly, the more physically demanding career twin had the same amount of degeneration as the less physically demanding career twin. There seems to be a disconnect from conventional wisdom. For the most part, scientists agree smoking is associated with increased disc degeneration. However, it was a bit of a surprise to see that activity levels, high demand versus moderate to less demand, did not have an effect on the amount of disk degeneration identified. With the study there's now more ongoing research on whether genetics is a significant contributing factor to development of disk degeneration. While the science is being debated; from a practical standpoint remember that potential does not mean achievement and predisposition does not mean certainty. We must still do the common-sense things to safeguard our spine, regardless of our genetics. Do not smoke. Do not gain weight. Exercise and maintain your core muscles. You cannot choose your parents, but you can choose to acquire healthy habits that will lead to a healthier and less painful spine. This is Dr. John Shim, discussing genetics in your spine. I hope you found this information interesting.
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