A Single Nucleotide Deletion resulting in Frameshift in Two Korean Neonates with Thyroxine-Binding Globulin Deficiency

Thyroxine-binding globulin (TBG) is a 54-kDa glycoprotein that is synthesized by the liver 1) . It is composed of a single polypeptide chain made of 395 amino acids. TBG is the major transport protein for thyroid hormones in the serum. The human TBG gene is located on the X chromosome (Xq22.2) 2) , and it consists of five exons spanning 5.5 kbp. Its structure and sequence are homologous to those of the genes encoding plasma serine protease inhibitors and cortisol-binding globulin 3) . The first exon (exon 0) is a short noncoding sequence 4) . Hereditary TBG abnormalities are manifested as complete TBG deficiency, partial TBG deficiency or TBG ex-