A POINT MUTATION (ALA229 TO THR) IN THE HINGE DOMAIN OF THE C-ERBA-BETA THYROID-HORMONE RECEPTOR GENE IN A FAMILY WITH GENERALIZED THYROID-HORMONE RESISTANCE

Various point mutations in the c-erbA thyroid hormone receptor (TR) beta-gene of unrelated kindreds have been reported to be responsible for different phenotypes of generalized thyroid hormone resistance. We now report a new point mutation, Td, in one of two TR-beta-alleles of three affected members of one family, designated family T. In contrast to the previously described point mutations, all located in the T3-binding domain of the TR-beta-gene, mutation Td was identified in the carboxy-terminal part of the hinge domain. Direct sequencing of the polymerase chain reaction-amplified whole coding region of the patients' fibroblast TR-beta-genes displayed a single guanine to adenine transition at cDNA nucleotide position 985. This altered alanine (GCC) to threonine (ACC) in codon 229. Garnier prediction of the consequence of the mutation indicated an altered secondary structure. The G --> A nucleotide substitution was not present in 80 random TR-beta-alleles, suggesting that this point mutation is responsible for generalized thyroid hormone resistance in family T. The in vitro expressed mutant TR-beta was shown to bind with high affinity to various thyroid hormone response elements. However, the affinity of the TR-beta to bind to T3 was reduced 3-fold, indicating that the hinge domain of the TR-beta is important for full ligand-binding activity. Moreover, it seems that multiple subdomains of the TR-beta interact cooperatively to achieve optimal T3 activity.