Increased familial clustering of autoimmune thyroid diseases.

Data regarding familial prevalence and recurrence risk ratio of autoimmune thyroid diseases (AITD) in Germany are lacking. The data from 179 German families of AITD patients encompassing 1 229 relatives were collected using standardized clinical and laboratory diagnostic criteria. Of this large collective, 86 AITD index cases with their 139 children and 106 AITD index cases with their 157 siblings were included. The familial prevalence was estimated by the recurrence risk ratio. This quotient indicates whether first degree relatives display an increased risk for developing AITD, compared with the general population. AITD were present in 14% of children and 15% of siblings of patients with AITD. Female gender was frequently affected in both offspring (female:male ratio=3:1) and siblings (11:1). Daughters (19%) and sisters (24%) were more frequently affected than sons (7%) and brothers (3%). The risk for developing AITD was 16-fold and 15-fold increased in children and siblings, respectively, of patients with AITD. In particular, children and siblings of index cases with Hashimoto's thyroiditis had a 32-fold and 21-fold increased risk, respectively, for developing immunthyroiditis. In comparison, the risk for developing Graves' disease was enhanced 7-fold in both children and siblings. The high prevalence of AITD in first degree, foremost female, relatives of patients with AITD demonstrates the importance of family history for developing AITD. Hence, regular screening of children and siblings of patients with AITD for presence of immunethyroiditis is recommended.