Are you the only member of your family that lives with an autoimmune disease?  Do you have more than one autoimmune disease, a condition known as polyautoimmunity?  We have talked about comorbidities, such as my dual diagnoses of MS and RA, but we haven’t talked much about autoimmune diseases which tend to cluster (aggregate) in our families.

Several studies have focused on an isolated autoimmune disease, often with complex genetic components, which might run in families (known as familial aggregation).  When the same autoimmune disease affects members of a family, it is referred to as familial autoimmune disease.  An example of this would be two sisters who both have lupus, or perhaps a mother and daughter who both have RA.

In my own family’s case, several female members have different autoimmune diseases, including RA, MS, lupus, scleroderma, and diabetes.  The aggregation of diverse autoimmune diseases that occur in a family (known as familial autoimmunity) has not been studied as extensively as familial aggregation.  Recently, researchers in Bogota, Colombia, conducted a systematic review and meta-analysis on the subject of familial autoimmunity, published in BMC Medicine (2013).

Familial autoimmunity was investigated in five major autoimmune diseases:
rheumatoid arthritis, systemic lupus erythematosus, autoimmune thyroid disease, multiple sclerosis, and type 1 diabetes mellitus.  Articles were searched in Pubmed and Embase databases and out of 61 articles discussing familial autoimmunity, 44 met criteria to be chosen for final analysis.

Familial autoimmunity was found in all the autoimmune diseases investigated.  Autoimmune thyroid disease, followed by systemic lupus erythematosus and rheumatoid arthritis, were the most frequent autoimmune diseases encountered.

Autoimmune thyroid disease, including Hashimoto’s thyroiditis and Graves’ disease, was significantly associated with the presence of type 1 diabetes mellitus, rheumatoid arthritis, pernicious anemia, systemic lupus erythematosus, celiac disease, vitiligo, and multiple sclerosis.  Compared with the general population, familial autoimmunity in Graves’ disease revealed that first degree family members were 14.1 and 13.5 times more likely to have pernicious anemia or RA, respectively.

Familial autoimmunity in rheumatoid arthritis was discussed in five articles, all of which linked autoimmune thyroid disease or type 1 diabetes to RA.  One study (Thomas, 1983) reported type 1 diabetes as the disease responsible for familial autoimmunity.  Researchers in another study (Taneja, 1993) stated that lupus, type 1 diabetes, autoimmune thyroid disease, Sjögren’s syndrome, psoriasis, and systemic sclerosis were also found in families with RA.  

In another research study (Hemminki, 2009), it was reported that when a parent had ankylosing spondylitis (an auto-inflammatory disease which tends to aggregate in families), the risk of several diseases in offspring was increased significantly.  Researchers determined the standardized incidence ratio (SIR) for each disease.  Values more than one indicate an increased frequency of what is expected, whereas a value below one indicates a decreased frequency.