These two distinct clusters of autoimmune diseases tend to run together within individuals and within families. For example, some 15% to 20% of people with Type 1 diabetes have at least the early manifestations of autoimmune thyroid disease (Graves disease or Hashimoto thyroiditis). Their first-degree relatives (parents, siblings, and children) are at increased risk of developing these disorders as well. People with Type 1 diabetes also have a slightly elevated risk for developing Addison disease.
An estimated 40% of families in which one member has Type 1 diabetes has another member with at least the early indications of autoimmune disease.