Are autoimmune diseases connected? I think yes!

A fellow Psoriatic Arthritis patient asked me to explain whether (and why) if someone has one autoimmune disease, they are more likely to get a second one. For example, in my case, is there some reason other than chance that I have both Psoriatic Arthritis and Celiac Disease?

To tell the truth... if I could answer that question I could win the Nobel prize and run a whole lot of people out of work. The immune system is incredibly complex, and a layperson like me can only skim the surface of understanding it.

Here's what I do know, however, after doing some sleuthing.

Yes, autoimmune diseases come in multi-packs, like underwear from Target. If you have one, you're likely to get two or three. This is called co-morbidity, btw. Just last month, an article in the American Journal of Epidemiology discussed some researchers' attempts to demonstrate autoimmune co-morbidity. The authors used public records to see how often rheumatoid arthritis, multiple sclerosis, autoimmune thyroiditis and insulin-dependent diabetes mellitus were present in the same individual. And they found that there was a high co-occurrence between rheumatoid arthritis, insulin-dependent diabetes mellitus and autoimmune thyroiditis. BUT... they found that there was an inverse relationship between RA and MS - which means that if you had one, you were LESS likely to have the other! Go figure. This reverse relationship does speak to a relationship... but what kind of relationship?

Dr. Noel Rose wrote an essay called The Common Thread discussing the etiology (the cause) of autoimmune diseases and the need for more research on the links between them. You can find the paper on the American Autoimmune Related Diseases Association website. Dr. Rose states:

Autoimmunity is an etiology: it is a cause of disease. Anatomically, autoimmune disease is very diverse; and that's why we see specialists in so many areas of medicine studying autoimmunity. They may be rheumatologists who are interested in joints; they may be dermatologists who are interested in skin; they may be cardiologists who are interested in the heart; they may be gastroenterologists who are interested in the gastrointestinal tract. But the common etiology for all of these disease--for Crohn's disease of the gut; for lupus of the skin; for rheumatoid arthritis of the joint--the common etiology that brings together all of these diseases is autoimmunity.

Dr. Rose doesn't necessarily say that one disease can cause another, but that's not what we're talking about. We're talking about whether they occur at the same time, and whether autoimmune diseases are all just one disorder with multiple symptoms. It does make sense that if you are having a problem with your immune system in general, that the problem won't always limit itself to one organ or region, but can be systemic. But how do we prove that all of these autoimmune diseases are related, or perhaps one underlying disease?

Here's one data point that suggests a connection: many different autoimmune diseases can be treated by the same medication - and I'm not just talking about diseases that look similar, like psoriatic arthritis and rheumatoid arthritis. For example, my husband and I could get Abbott labs to give us a bulk discount - Humira treats PsA and Crohn's Disease. Humira is a TNF-alpha blocker - and both of our diseases can be linked to an excess of TNF-alpha. On the other hand, so far, Humira doesn't seem to treat every auto-immune disease.

In their book "The Autoimmune Connection" Rita Baron-Faust, Jill P. Buyon, M.D. hypothesize about some of the reasons autoimmune diseases may co-occur, or may perhaps be one disease with multiple symptoms. They say:

While autoimmune diseases may target different areas of the body, the genes that affect immune responses may be the same. For example, genes that govern cytokines may have a mutation that causes too many inflammatory molecules to be released. Defective genes common to autoimmune diseases may also affect the way T-cells are programmed to recognize antigens, the number of receptors they carry, the number of T-cells with a faulty memory, or how many defective T-cells are eliminated.

Researchers are now trying to demonstrate, on a genetic level, that many autoimmune diseases are related. A group of researchers looked across 42 separate studies of 11 autoimmune diseases to see if they could find underlying genetic links. They found that several diseases shared some common genetic fingerprints (the HLA region of chromosome 6 lit up for many autoimmune diseases, as did many parts of chromosome 16). On the other hand, there were several genes that seemed to be involved with only one disease. This is from the Feb 2009 issue of the European Journal of Human Genetics - you can read the abstract here.

So, ok, what do we know about autoimmune co-morbidity? What do we think? Here's what I've learned:

• Many autoimmune diseases are likely to co-occur in the same person, but some aren't.
• Many researchers think that separate autoimmune diseases have a shared etiology, or cause, and may possibly be one disease. Some evidence supports this, but some doesn't.
  
• Many autoimmune diseases share similar genetic links, but not in all cases.

What does this mean? Folks, it means that we need more research. And of course, this means we need more funding for research. If you haven't yet, find some way to support research on your disease(s), or autoimmune disease in general. Go to the NPF website, or the AARDA website. Do something, and keep talking.

It also speaks to something I've discussed before in my blog - the fact that humans' compulsions to put things in boxes - to categorize - may limit how we understand disease. Maybe autoimmune diseases are all just one disease... maybe they aren't, but they just share a lot of qualities or root causes. Do the diagnostics get in the way of knowledge? I think yes, sometimes. Perhaps a more holistic approach to research, diagnosis, and treatment would help use understand these symptoms (not diseases) better.

It also means I have a lot more to learn before I ever attempt to write a logical post about this topic again. This is complicated stuff.