by C. Thomas Dow, M.D.
An inadvertent researcher
I am an ophthalmologist; more than fifteen years ago I saw a patient who had an inflammatory condition in her eye that suggested a systemic disease, sarcoidosis. These patients frequently have an inflammatory mass in the lungs as well. She had imaging showing a lung mass and that was followed by a biopsy. The biopsy confirmed sarcoidosis Decades before this I received a degree in microbiology and learned of Mycobacterium avium ss. paratuberculosis, MAP. Because of that, I was aware of the long controversy surrounding MAP and Crohn’s disease; and a second disease that has been historically associated with MAP – sarcoidosis. Recalling that, I sent a portion of the lung biopsy to a lab that had the expertise to do a DNA probe for MAP. The test was positive. Time-wise, this coincided with broader use of the internet and the full access to the National Library of Medicine via PubMed. The availability of this vast resource combined with the excitement of finding MAP in the lung tissue of this particular patient stimulated me to perform regular “shotgun” searches of medical and veterinary literature (e.g. MAP, Crohn’s, sarcoidosis AND genetics) that would shed more light on the role of MAP in human diseases. The fruits of these searches and subsequent collaborations with REAL researchers are described in this summary.
“All roads lead to Rome” is the old axiom that described the central place the city of Rome played in its millennial world empire.
All roads lead from Crohn’s – this narrative discusses human diseases associated with MAP other than Crohn’s disease. For our purposes these roads are trails; genetic trails.
There are several genetic “defects” that impart susceptibility to Crohn’s disease. Interestingly, some of these genetic defects are also associated with susceptibility to mycobacterial infection – recall MAP is a mycobacteria (“cousin” to the mycobacteria that cause tuberculosis and leprosy.) Even more interesting is the fact that some of these defects are associated with other diseases. To date the diseases on these genetic trails implicating MAP include: sarcoidosis, Blau syndrome, autoimmune (Hashimoto’s) thyroiditis, autoimmune diabetes (T1DM) multiple sclerosis and lupus erythematosis. Wow, not so fast!
So there are genetic trails associated with Crohn’s that can be followed to investigate the other diseases on the trail to see if people with these diseases also have evidence of a MAP infection.
The first of these genetic trails was discovered in 2002 and was first called NOD2, now called CARD15. (Sorry for the alphanumeric names and the fact that they are subject to change – out of my control.) The CARD15 gene is associated with the ability to recognize bacteria. A loss-of-function defect of the CARD15 gene allows bacteria to persist undetected. This defect was found, not only in a good percentage of individuals with Crohn’s, but also in a rare disease: Blau syndrome. (There are components of genes called domains. The Crohn’s and Blau defects are on different domains of the CARD15 gene). An additional inflammatory condition is on this same genetic trail: psoriatic arthritis – low hanging fruit for a rheumatology researcher!
Blau syndrome is a multi-system inflammatory disease that, though rare, is interesting in that it is the only inflammatory disease that is inherited in an autosomal dominant pattern. (If you inherit the abnormal gene from only one parent, you can get the disease.) There can be several family members who have manifestations of the disease. Individuals who have no family members with the disease (“sporadic”) all have a new, “de novo”, genetic defect of the CARD15 gene in the domain associated with Blau syndrome. Because of the features of the disease, Blau syndrome is frequently called “juvenile sarcoidosis.” These two clues – sharing a gene defect with Crohn’s disease and looking like sarcoidosis – both associated with MAP, made me suspect that MAP may be the trigger of Blau syndrome. I contacted authors of articles about Blau syndrome in which there were pathologic specimens. I received six specimens from five different patients representing three different families. The specimens included synovium from joints afflicted with the arthritis associated with Blau syndrome, skin from areas of dermatitis, and inflammatory masses from the liver and kidney. All tissues tested positive for the DNA of MAP. In 2005 this information was presented in Copenhagen at the International Association for Paratuberculosis meeting.
Type I Diabetes
There is another genetic defect associated with Crohn’s disease: originally named NRAMP1, now called SLC11a1. Defects in the SLC11a1 gene are associated with both susceptibility to mycobacterial infections (including tuberculosis, leprosy and paratuberculosis – of cattle, sheep and goats) and a host of inflammatory diseases besides Crohn’s disease: autoimmune thyroiditis (Hashimotos’s), rheumatoid arthritis, Addison’s disease, multiple sclerosis, primary biliary cirrhosis and autoimmune diabetes, (Type 1 diabetes, T1DM). The SLC11a1 gene is responsible for killing bacteria – loss of the function of the gene is another manner in which mycobacteria can persist.
At the same Copenhagen meeting I gave a second presentation suggesting the MAP may be a trigger of several other diseases including T1DM. I presented the SLC11a1 connection between Crohn’s and T1DM. The proposed mechanism was that of “molecular mimicry.” In humans and in bacteria there are protective proteins made in response to stress called heat shock proteins. Mycobacteria are particularly capable of producing a protective protein, heat shock protein 65 (Hsp65). Unfortunately, there are human proteins that look similar to the mycobacterial Hsp65. The first one detected was a protein in the pancreas, glutamic acid decarboxylase or GAD. When a child is deemed to be at risk of developing T1DM (parents or siblings with T1DM) they are followed with blood tests looking for anti-GAD antibodies. Presence of these antibodies heralds T1DM. In simpler terms, what is suggested is that a persistent MAP bacteria produces its protective protein. Because this protein looks like a protein in the pancreas, an immune response against the MAP protein also is an immune response against the pancreas, and the insulin producing cells of the pancreas are destroyed by the collateral damage – all because genetically, MAP could not be killed in the first place. Moreover, I reiterate the known association of early exposure to cow’s milk and T1DM.
At the social event accompanying the Copenhagen meeting, I was approached by a notable MAP researcher, Dr. Leonardo Sechi. He said that he was particularly interested in the presentation about MAP and T1DM because in addition to the common paratuberculosis infection in sheep, his island of Sardinia also has the highest incidence in the world of T1DM (tied with Finland). He said that he was going to look for MAP in individuals with T1DM. Fast forward to 2013, and Dr. Sechi has published several studies linking MAP and T1DM (and some studies linking MAP multiple sclerosis.)
Autoimmune (Hashimoto’s) Thyroiditis
An internet PubMed search led me to clinicians in Italy who had published a case report of an individual with “orofacial granulomatosis” and autoimmune thyroiditis. Orofacial granulomatosis is sometimes thought of a different manifestation of Crohn’s disease. With Crohn’s and autoimmune thyroiditis both on the SLC11a1 genetic trail, I suspected that MAP may be involved. With the help of Dr. Michael Collins’ lab in Madison, Wisconsin and transatlantic one-day delivery, blood samples from these patients were cultured for MAP; and with the time and expertise required for such culture, MAP was grown from their blood. A follow-up of other family members with autoimmune thyroiditis yielded similar cultures positive for MAP. The same molecular mimicry was postulated as the mechanism by which MAP Hsp65 cross reacts with thyroid proteins causing damaging inflammation to the thyroid.
Systemic lupus erythematosis (SLE) is another systemic inflammatory disease that is on the SLC11a1 trail. A patient of mine with biopsy proven SLE agreed to have her blood tested for the presence of MAP. Again, with the assistance and expertise of Dr. Collins’ lab, MAP was successfully grown from her blood. A well used molecular tool for comparing DNA or proteins is called BLAST analysis. A BLAST comparison was made comparing the Hsp65 protein of MAP with anti-Ro and anti-La (antibodies common in SLE.) Significant homology (similarity) was demonstrated.
Conclusion: How Does MAP Cause Disease?
In summary, this narrative proposes that, in a genetically susceptible individual, MAP is able to maintain a persistent presence. If a granuloma is a main feature of the disease (Crohn’s, sarcoidosis, Blau syndrome), it suggests that MAP is the precipitant infectious agent and is part of the granuloma. If antibodies are the main feature of the disease (autoimmune thyroiditis, multiple sclerosis, T1DM, SLE), persistent MAP evokes the harmful auto-antibodies via molecular mimicry. A third manner by which MAP may cause disease is by exhausting the immune system. Recently, MAP has been suggested to have a causal role in Parkinson’s disease. In an age-dependent manner, MAP may burden the immune system to the degree that it can no longer keep MAP in check. Work by Dr. Sechi suggests MAP involvement in Parkinson’s. Another genetic “coincidence”: the gene LRRK2 shares genetic risk for both Parkinson’s and Crohn’s – all roads lead from Crohn’s.
The examples listed here may give the impression that sorting out MAP and human disease is similar to a board game that can be performed with the clarity of checkers – not so. There are likely combinations of genetic susceptibilities that determine the consequence of MAP infection. There are also likely windows of vulnerability as well as dose of MAP exposure, age at exposure, hormonal state and immune health that determine the consequence of an exposure to MAP.
About the Author
Dr. C. Thomas Dow received his bachelor of science degree from the University of Wisconsin-Madison in microbiology, and attended medical school at the University of Wisconsin School of Medicine, Madison. Following medical school, he did an internship year at Bronson Methodist Hospital in Kalamazoo, Michigan, and completed his ophthalmology residency at the University of Wisconsin Hospital and Clinics. Dr. Dow is Board Certified in Ophthalmology, is licensed in Wisconsin, and is included in the Best Doctors in America database. He established Chippewa Valley Eye Clinic in 1978. He has served as a member of the surgical team, Free Rural Eye Clinic, in the Philippines several times. In addition to seeing patients, Dr. Dow has research interests in infectious causes of immune disease and in telomerase in oncology and regenerative medicine.