A case of complete deficiency of total thyroxine-binding globulin (TBG) associated with Graves disease
Doo-Man Kim1, Hyeon Kyu Kim1 & Soon Jib Yoo2
Thyroxine-binding globulin (TBG), the major transport protein for thyroid hormone in circulation, is synthesized in the liver. Complete TBG deficiency was first reported in 1964, and in 1991 a single nucleotide deletion was found in the first base of the codon for amino acid 352 of the common-type TBG molecule. This mutation causes a frameshift in translation and premature termination. Most people with abnormal TBG concentrations are euthyroid. Cases of Graves disease with periodic paralysis and complete deficiency of TBG have rarely been reported.
We here describe a 28-year-old male with total thyroxine-binding globulin (TBG) deficiency associated with Graves disease. He experienced symptoms of periodic paralysis for several days before admission. His thyroid function showed low TSH (<0.01 uIU/ml) and elevated free T4 level (3.86 ng/dl), but total T3 concentration was normal (100 ng/dl). Other test results are as follows: total T4; 4.0 ug/dl, TSH binding inhibitory immunoglobulin (TBII); 51.1%, and TBG level <1.0 ug/ml.
Allele specific PCR and DNA sequencing of the patient revealed a single nucleotide deletion was found in the first base of the codon for amino acid 352 of the TBG. We treated him with methimazole and followed.