The epidemiology of Graves' disease: evidence of a genetic and an environmental contribution.

Previous family and twin studies have indicated that Graves' disease has a heritable component. Family studies have also shown that some autoimmune disease cluster in families and genetic studies have been able to show shared susceptibility genes. In the present nation-wide study we describe familial risk for Graves' disease among parents and offspring, singleton siblings, twins and spouses with regard to age of onset, gender and number and type of affected family members. Additionally familial association of Graves' disease with any of 33 other autoimmune and related conditions was analyzed. The Swedish Multigeneration Register on 0-75-year-old subjects was linked to the Hospital Discharge Register from years 1987-2007. Standardized incidence ratios (SIRs) were calculated for individuals whose relatives were hospitalized for Graves' disease compared to those whose relatives were unaffected. The total number of hospitalized Graves' patients was 15,743. Offspring with an affected family member constituted 3.6% of all patients among offspring. The familial SIR was 5.04 for individuals whose sibling was affected but it increased to 310 when two or more siblings were affected; the SIR in twins was 16.45. Familial risks were higher for males than for females. The SIR was increased to 6.22 or 30.20 when parental age was limited to 50 or 20 years, respectively. Graves' disease associated with 19 other autoimmune and related conditions, including Addison's disease, type 1 diabetes mellitus, Hashimoto/hypothyroidism, pernicious anemia, polymyositis/dermatomyositis, myasthenia gravis, discoid lupus erythematosus and localized scleroderma. Remarkably, there was a high disease concordance of 2.75 between spouses. The clustering between spouses suggests environmental effects on Graves' disease which may contribute to the observed gender effects. The demonstrated high risks should be considered in clinical counseling and in prevention plans.