While the basic purpose of the immune response is to save us from infections, something goes awry in these autoimmunity cases where the immune system chooses to respond to itself, rather than the foreign pathogen.
AI conditions tend to run together, in families and in individuals. You can develop an AI disease without a family history of AI, but that doesn’t mean the genes weren’t always there, in your family’s gene pool.
On the flip side, someone could have the right genes for the perfect autoimmune condition, but not get the disease. AI conditions are multifactorial and require a genetic predisposition, plus an environmental trigger. The conditions must be perfectly aligned and just so for an autoimmune condition to present itself.
There are lots of these genes at play in these scenarios. But some very important ones involved are what are called major histocompatibility complex (MHC) genes. These particular genes—proteins, to be more specific—are found on all jawed vertebrate DNA. In humans, they’re known as human leukocyte antigen (HLA) genes. These genes sit on top of cells and present samples of what’s going on inside and around the cell to our immune system, instructing it what to and what not to attack.
Certain HLA types are heavily associated with certain types of AI disease, particularly, class II HLA genes.
About 40-50% of the risk for type 1 diabetes is estimated to come from HLA genes alone. Different HLA types have been associated with almost every single AI disease, some stronger than others. HLA gene HLA-B27 is found in 95% of people with ankylosing apondylitis (a type of arthritis) and strongly correlates with the expression of other AI diseases, like Behçet's disease, celiac disease, and rheumatoid arthritis.
But some of these types are associated with more than just one AI condition. Which means often, autoimmune diseases show up in clusters. Type 1 diabetes, for example, is associated with HLA types DQ2 and DQ8, with associated alleles DR3 and DR4. Similarly, Hashimoto’s and celiac disease are both strongly associated with these exact same HLA types.
That's why if you have one AI, it’s a good idea to have your endocrinologist or primary care physician regularly screen you for others.
Of course, this doesn’t mean that if you have one autoimmune condition you are guaranteed to have the other HLA types. It also doesn’t guarantee that even if you do have all HLA types that you will develop the other conditions associated with those HLA genes, or even that these are the only AI diseases you may be at risk.
It is widely accepted in medicine that autoimmunity is a risk factor for autoimmunity, so if you have one AI disease you are at risk for others. I personally have type 1 diabetes and Hashimotos, and so many other AI diseases run in my family.
The world of autoimmunity is truly mind blowing. And one thing to keep in mind: those external triggers can often be set off by diet. Adhering to a low inflammatory way of eating (and lifestyle) can have truly remarkable outcomes.