"Is interstitial cystitis genetic" is a question we get asked a lot. Many people have noticed that IC runs in their family, or remember another family member who struggled with similar symptoms, even if they weren't diagnosed. And parents want to know whether they should be on the lookout for their children. We discuss the topic in more depth in The Interstitial Cystitis Solution, but the answer, as with most things about IC, is complicated.
Gene-Environment Interaction
When we talk about how genes affect our health and other traits, there are two areas that we need to understand.
Genetic Component: Some traits or conditions are 100% genetic - if you have the gene, you will certainly have the trait. Eye color is an example of a determined trait, and Huntington's disease is also 100% genetic.
Environmental Component: The other important aspect is the environment. There are obviously conditions that are determined solely by the environment - a papercut, as an easy example, or an infection. These don't care about your genes at all, it's just a factor of the environment.
The difficulty when we talk about conditions is that they are almost always some combination of genes and environment; researchers refer to this as gene-environment interaction. An easy example is height - obviously much of how tall we grow is determined by our parents, but it's also affected by many other things, including what we eat growing up, how much we exercise, and other factors. It's entirely possible to have two identical twins with the exact same DNA, raised in different environments, with a significant height difference or other physical differences.
The most important study with regards to interstitial cystitis studied identical twins (again, with the exact same DNA), and found that about 50% of siblings would also have IC when one was diagnosed. This clearly shows that IC can't be entirely genetic (otherwise 100% of siblings would have it), but that it's not solely environmental (in that case we would expect only about 10% of siblings to have it, the same as the general population). What we are seeing is that there is a gene-environment interaction; your genes make you more susceptible or predisposed to IC, but they are not destiny. More research is certainly needed to try and understand what environmental factors may be contributing to IC.
Underlying Genetic Component?
New research is focusing on trying to determine if there is an underlying genetic component that could be contributing not only to interstitial cystitis, but also to conditions like fibromyalgia and constipation, which are more prevalent in interstitial cystitis patients. A 2015 research paper looked at nearly 250 IC patients, and examined their first-degree (parents/siblings/children) and second-degree (aunts/uncles, nephews/nieces, grandparents) relatives.
They looked at a variety of conditions that patients with IC are more likely to experience, and found two that were more common in IC patients themselves, their first-degree, and their second-degree relatives. Fibromyalgia (or generalized myalgia) and constipation were more likely among all groups. This implies a solid genetic link between the conditions.
This new connection may help researchers as they try to pin down the genetic component of IC, which may help to identify people who are at risk for the condition.
Additional Resources
Dr. Nicole Cozean is the founder of PelvicSanity physical therapy, Orange County's premier pelvic floor physical therapy clinic. One of only 270 PTs to be board-certified in the pelvic floor, and the first PT to serve on the ICA Board of Directors, Nicole is the author of the acclaimed and best-selling book The Interstitial Cystitis Solution (2016). She is an adjunct professor at her alma mater, Chapman University. The PelvicSanity blog focuses on presenting practical, positive information to help patients beyond the walls of Nicole's clinic.