How is vitiligo related to thyroid disease?

Current research points to a genetic component in autoimmune diseases. However, autoimmune diseases are not typical genetic diseases where there is a specific gene mutation. With autoimmune diseases, multiple genes are involved that collectively increase vulnerability or susceptibility. Therefore, what is inherited is not one specific gene but several genes that increase risk. As a result, autoimmune diseases tend to "cluster" in families - not as one particular disease, but as a general tendency to the autoimmune process and, consequently, different autoimmune diseases.

The "cluster" of autoimmune diseases associated with vitiligo includes Hashimoto's Thyroiditis (hypoactive thyroid), Graves' Disease (hyperactive thyroid), adrenocortical insufficiency (underproduction of corticosteroid hormone by the adrenal gland), rheumatoid arthritis, type 1 diabetes, psoriasis, systemic lupus erythematosus, and pernicious anemia (subnormal red blood cell level caused by inability to absorb vitamin B12), so one family member could have Hashimoto's Thyroiditis; another, type 1 diabetes; another, rheumatoid arthritis.