A firm cause is not available. They suspect that it is autoimmune with a POSSIBLE familiar connection, so many have a primary AI such as thyroid related illness. Genetic is possible, but not much studying is being done, environment well how far do we go, they put fluoride in our public water in the 40's. Since then they have discovered that fluoride is a major contributor to thyroid disease which is a huge base for LS. We do know it is not a sexually transmitted disease.