TSH receptor (TSHR) germline mutations occur as activating mutations in familial non-autoimmune hyperthyroidism (FNAH) or sporadic non-autoimmune hyperthyroidism (SNAH). Up to date 17 constitutively activating TSHR mutations have been reported in 24 families with FNAH. The diagnosis of FNAH should be considered in cases with a positive family history, early onset of hyperthyroidism, goiter, absence of clinical stigmata of autoimmunity and recurrent hyperthyroidism. Moreover, 14 subjects with sporadic non-autoimmune hyperthyroidism and 10 different TSH receptor germline mutations have been reported. The main characteristic of SNAH is a negative family history. Additional consequences of prolonged neonatal hyperthyroidism (mental retardation, speech disturbances and craniosynostosis) have often been reported in SNAH. No genotype-phenotype relationship has been reported in patients with germline TSHR mutations. There is no association of in vitro activities determined by linear regression analysis (LRA) and several clinical indicators of hyperthyroidism activity for SNAH. However, the comparison of the LRA values of sporadic TSHR mutations with LRA values of familial TSHR mutations does show a significantly higher median LRA value for sporadic as compared to familial autosomal dominant hyperthyroidism. This finding is in line with the clinical impression of a more active clinical course in patients with SNAH. However, additional genetic, constitutional or environmental factors are most likely responsible for the phenotypic variations of the disease and the lack of correlation between in vitro activities of the TSHR mutations and the severity of hyperthyroidism. (C) 2010 Elsevier Ireland Ltd. All rights reserved.