Background: Thyroglobulin (TG) defect is a rare cause of congenital hypothyroidism. Although only 44 mutations of the human TG gene have been identified, we have suspected a TG defect in 38% of Taiwan Chinese children/adolescents presenting with moderate or severe thyroidal dyshormonogenesis.
Study objective: The aim of the study is to report the discovery of new TG gene mutations and associated clinical manifestations of the defective TG protein.
Patients and results: In seven patients from six families, we detected six new TG gene mutations, including c.1348delT, p.R432X (c.1351C>T), g.IVS3 + 2T>G, c.1712delT, p.Q1765X (c.5350C>T), and c.6047delA. The c.1348delT and p.R432X mutations were the most common, detected in 33 and 25%, respectively, of alleles studied. Haplotype analysis suggested that the c.1348delT and g.IVS3 + 2T>G mutations are due to founder effects, whereas p.R432X is probably due to independently recurrent de novo mutations. mRNA transcript of the g.IVS3 + 2T>G mutant, detected in whole blood by reverse transcription-nested PCR, showed skipping of exon 3 (98-bp deletion) and a frameshift, with a terminal signal after 17 altered amino acid residues.
Conclusions: TG defects have an important role in severe thyroidal dyshormonogenesis (pretreatment, or after a 3-wk T(4) withdrawal, plasma T(4) < or = 30 nmol/liter) in Taiwanese. Its genetic characteristics are markedly different from those described in other populations presenting with mutations of the TG gene.