Complete thyroxine-binding globulin (TBG) deficiency produced by a mutation in acceptor splice site causing frameshift and early termination of translation (TBG-Kankakee).
Fourteen T4-binding globulin (TBG) variants have been identified at the gene level. They are all located in the coding region of the gene and 6 produce complete deficiency of TBG (TBG-CD). We now describe the first mutation in a noncoding region producing TBG-CD. The proband was treated for over 20 yr with L-T4 because of fatigue associated with a low concentration of serum total T4. Fifteen family members were studied showing low total T4 inherited as an X chromosome-linked trait, and affected males had undetectable TBG in serum. Sequencing of the entire coding region and promoter of the TBG gene revealed no abnormality. However, an A to G transition was found in the acceptor splice junction of intron II that produced a new HaeIII restriction site cosegregating with the TBG-CD phenotype. Sequencing exon 1 to exon 3 of TBG complementary DNA reverse transcribed from messenger RNA of skin fibroblasts from an affected male, confirmed a shift in the ag acceptor splice site. This results in the insertion of a G in exon 2 and causes a frameshift and a premature stop at codon 195. This early termination of translation predicts a truncated TBG lacking 201 amino acids.
Department of Medicine, The University of Chicago, Illinois 60637, USA.
G A
GA
Carvalho
R E
RE
Weiss
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S
Refetoff
D000595:Amino Acid Sequence; D001483:Base Sequence; D004251:DNA Transposable Elements / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004274:DNA, Recombinant / Q000235:genetics; D005260:Female; D016368:Frameshift Mutation / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D014176:Protein Biosynthesis / Q000235:genetics*; D013960:Thyroid Function Tests; D013975:Thyroxine-Binding Proteins / Q000172:deficiency* / Q000235:genetics*
D004251:DNA Transposable Elements; D018076:DNA, Complementary; D004274:DNA, Recombinant; D013975:Thyroxine-Binding Proteins