How far are we from understanding the genetic basis of Hashimoto's thyroiditis?

Hashimoto's thyroiditis (HT), an autoimmune thyroid disease (AITD), is becoming more and more prevalent in the recent years. Data on family and twin studies carry evidence for strong genetic influence on AITD susceptibility and development. The most common approaches to unravel the background of those diseases are whole genome screening and candidate gene analysis. Common Hashimoto's thyroiditis and Graves' disease (GD) genes have been identified, as well as genes that are characteristic for only one of those diseases. Because of the complex nature of AITD, caused by their polygenic nature and a complex mode of inheritance, there are still more questions to be answered than answers that can be given, especially about the nature of Hashimoto's thyroiditis. There are plenty of papers concerning the pathogenesis of AITD. However, not seldom do they end up in conclusions about GD, because the results for this disease are far clearer and more unambiguous than those obtained for HT. Similarly, meta-analyses and especially reviews most often concentrate on AITD in general or on GD alone. In this review, Hashimoto's thyroiditis is the main player. It aims to review the state of the art about the background of the development of this disease.