Tadashi Morimura

Novel Inactivating Missense Mutations in the Thyrotropin Receptor Gene in Japanese Children with Resistance to Thyrotropin

We describe Japanese siblings with resistance to thyrotropin (TSH) who are compound heterozygotes for two novel mutations in the TSH receptor gene. The affected siblings had increased serum TSH, normal serum thyroid hormones, and normal positioned but slightly hypoplastic thyroid glands. The mutated paternal allele has the substitution of His (CAC) in place of Arg (CGC) at codon 450 (R450H) of the TSH receptor. The mutated maternal allele has the substitution of Ser (AGT) in place of Gly (GGT) at codon 498 (G498S) of the TSH receptor. COS-7 cells transfected with the R450H mutant exhibited a slightly decreased TSH binding and a slightly decreased cyclic adenosine monophosphate (cAMP) response to TSH, whereas cells transfected with the G498S mutant exhibited a markedly decreased TSH binding and a markedly decreased cAMP response to TSH. Flow immunocytofluorometry analysis demonstrated that the G498S mutant resulted in extremely low expression at the cell surface as compared with the wild type receptor and the R450H mutant, in spite of a normal intracellular synthesis. The present cases are the first Japanese patients with TSH resistance in whom mutations in the TSH receptor gene have been identified. These novel mutations may contribute to understanding of the struc-ture-function relationship of the TSH receptor.

Assignment of type II iodothyronine deiodinase gene (DIO2) to human chromosome band 14q24.2-->q24.3 by in situ hybridization.

Type II iodothyronine deiodinase (DII) catalyzes the activation of the thyroxine to 3,3),5-triiodothyronine (T3). In contrast to type I iodothyronine deiodinase (DI), DII is present in limited tissues and is considered to play a pivotal role to provide local T3 (St Germain et al., 1997). Recently, a partial human DII cDNA clone was isolated (Croteau et al., 1996). Although the human DI gene (DIO1) was mapped to chromosome 1p33→p32 by fluorescence in situ hybridization (FISH) (Jakobs et al., 1997), the chromosome location of human DII gene (DIO2) has not been determined by FISH. Here we isolated human DIO2 and determined the location of the gene to chromosome 14q24.2→q24.3 by FISH. During the course of this study, Celi et al. (1998) independently reported that the human DII gene was mapped to chromosome 14q24.3 by using somatic cell hybrid panels.

Frequency and Clinical Implication of the R450H Mutation in the Thyrotropin Receptor Gene in the Japanese Population Detected by Smart Amplification Process 2

In Japanese pediatric patients with thyrotropin (TSH) resistance, the R450H mutation in TSH receptor gene (TSHR) is occasionally observed. We studied the frequency and clinical implication of the R450H mutation in TSHR in the general population of Japanese adults using smart amplification process 2 (SmartAmp2). We designed SmartAmp2 primer sets to detect this mutation using a drop of whole blood. We analyzed thyroid function, antithyroid antibodies, and this mutation in 429 Japanese participants who had not been found to have thyroid disease. Two cases without antithyroid antibodies were heterozygous for the R450H mutation in TSHR. Thus, the prevalence of this mutation was 0.47% in the general population and 0.63% among those without antithyroid antibodies. Their serum TSH concentrations were higher than the average TSH concentration not only in subjects without antithyroid antibodies but also in those with antithyroid antibodies. The R450H mutation in TSHR is relatively common in the Japanese population and potentially affects thyroid function. The present study demonstrates that the SmartAmp2 method is useful to detect the R450H mutation in TSHR, which is one of the common causes of TSH resistance in the Japanese population.