Autoimmune disease- is the body fighting with an absorbed twin?

Autoimmune diseases are the 3rd leading cause of morbidity and mortality in the industrialized world, surpassed only by cancer and heart disease. Nearly 80% of those affected with an autoimmune disease are women, usually of childbearing age or women under age 65. The National Institute for Health estimates that there are now 23 million Americans with an autoimmune condition, and that number is on the rise. To put that into perspective, 9 million Americans are affected by cancer. 

This is a quote from an excellent web site explaining all kinds of autoimmune disease and suggesting ways to combat them.   But at no stage does Paula Owens mention the possibility that the cells in the body being attacked may in fact belong to an absorbed twin.  

Chimerism is the state  where two different cell  lines coexist in ide the body of one individual. An obvious reason for chimerism is the merging of two embryos, but what is the two embryos are two identical twins?   What if you have your own monozygotic twin's cells dividing inside you and forming certain tissues, but the DNA is just slightly different - different enough in fact to trigger an immune response?

Chimerism is already recognised as a cause of autoimmune reaction.

Unfortunately, the whole issue is clouded by the fact that  researchers use twin studies to see if a disease is genetically inherited or not, which in this case defeats the whole argument.  You cant carry out a study of twins and non-twins if you don't know if the non twins are womb twin survivors or not, and if the twins are reduced triplet sets or not.  [sigh]

[There is lots more on this in my book  "Womb twin survivors"]