Gene screening of thyroxine-binding globulin (TBG) deficiencies in the Japanese: only two mutations account for TBG deficiencies in the Japanese.

T4-binding globulin (TBG) is the principal transport protein for thyroid hormone in the circulation. Twelve mutations in the human TBG gene have been reported, and the inheritance of those variant TBGs was shown to be X-chromosome linked. We previously reported a nucleotide deletion at the codon 352 (TBG-CDJ) and a nucleotide substitution at the codon 362 (TBG-PDJ) of the TBG gene in a Japanese male manifesting TBG complete deficiency and partial TBG deficiency, respectively. In this communication we investigate the prevalence of both mutations among 50 unrelated Japanese subjects manifesting complete or partial TBG deficiency from various areas of the Japanese Archipelago. Mutant alleles were identified by amplification of their genomic DNAs by PCR with allele-specific primers. In addition, the presence of a polymorphic mutation in codon 283 (TBG-Poly) in these variants was investigated. All male subjects manifesting complete TBG deficiency (n = 30) and all female subjects manifesting partial TBG deficiency (n = 4) were demonstrated to be hemizygotes and heterozygotes for the mutation of TBG-CDJ, respectively. All male subjects manifesting partial TBG deficiency (n = 16) were shown to have the mutation of TBG-PDJ as hemizygotes. TBG-Poly was consistently absent from these variants. We conclude that only TBG-CDJ and TBG-PDJ may account for complete and partial TBG deficiencies in the Japanese.