Case Report
Copyright ©The Author(s) 2019. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Clin Cases. Nov 26, 2019; 7(22): 3887-3894
Published online Nov 26, 2019. doi: 10.12998/wjcc.v7.i22.3887
Novel frameshift mutation causes early termination of the thyroxine-binding globulin protein and complete thyroxine-binding globulin deficiency in a Chinese family: A case report
Ping-Ping Dang, Wei-Wei Xiao, Zhong-Yan Shan, Yue Xi, Ran-Ran Wang, Xiao-Hui Yu, Wei-Ping Teng, Xiao-Chun Teng
Ping-Ping Dang, Wei-Wei Xiao, Zhong-Yan Shan, Ran-Ran Wang, Xiao-Hui Yu, Wei-Ping Teng, Xiao-Chun Teng, Department of Endocrinology and Metabolism, Institute of Endocrinology, Liaoning Provincial Key Laboratory of Endocrine Diseases, The First Hospital of China Medical University, Shenyang 110001, Liaoning Province, China
Yue Xi, Department of Endocrinology and Metabolism, The Third Affiliated Hospital of Jinzhou Medical University, Jinzhou 121000, Liaoning Province, China
Author contributions: Teng WP, Shan ZY, and Teng XC reviewed the literature and contributed to manuscript drafting and the clinical description; Wang RR and Yu XH collected the clinical data and blood samples from the family members; Xi Y and Xiao WW carried out the gene polymorphism screening; Dang PP prepared the figures, contributed to the molecular genetic description, and wrote the manuscript; all authors issued final approval for the version to be submitted.
Supported by the National Natural Science Foundation of China, No. 81570711; National Clinical Key College Fund and the Key Platform Foundation of Science and Technology for the Universities in Liaoning Province, No. 16010.
Informed consent statement: Written informed consent was obtained from the participants for publication of this report and any accompanying images.
Conflict-of-interest statement: The authors declare that they have no competing interests.
CARE Checklist (2016) statement: The authors have read the CARE Checklist (2016), and the manuscript was prepared and revised according to the CARE Checklist (2016).
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Corresponding author: Xiao-Chun Teng, MD, PhD, Professor, Department of Endocrinology and Metabolism, The Endocrine Institute and The Liaoning Provincial Key Laboratory of Endocrine Diseases, The First Hospital of China Medical University, No. 155, Nanjing North Street, Heping District, Shenyang 110001, Liaoning Province, China. tengxiaochun@126.com
Telephone: +86-24-83283294
Received: April 29, 2019
Peer-review started: April 30, 2019
First decision: August 1, 2019
Revised: October 17, 2019
Accepted: October 30, 2019
Article in press: October 30, 2019
Published online: November 26, 2019
Abstract
BACKGROUND

Thyroxine-binding globulin (TBG; the gene product of SERPINA7) is the main transporter of thyroid hormones in humans. Mutations in the TBG gene may lead to inherited TBG deficiency. There have been 28 reported mutations that associate with complete TBG deficiency (TBG-CD). Here we identified a novel frameshift mutation causing early termination of the TBG protein and TBG-CD in a Chinese family.

CASE SUMMARY

A 46-year-old Chinese man was referred to our hospital with normal free thyroxine, free triiodothyronine, thyrotropin, but lower total thyroxine and total triiodothyronine, and undetectable serum TBG, indicative of TBG-CD. Blood samples were obtained from the patient’s family members and thyroid function and serum TBG were evaluated. Genomic DNA from peripheral blood was sequenced to detect possible TBG mutation(s). Quantitative PCR high-resolution melting curve analysis was used to screen TBG-Poly (L283F) among 117 Chinese men. A novel mutation of TBG (p.Phe135Alafs*21), a 19-nucleotide insertion in exon 1, was identified, which resulted in a truncated TBG protein product and caused TBG-CD. The other mutation, identified in the proband’s father, is a known polymorphism, TBG-Poly (L283F). The frequency of the TBG-Poly allele among 117 unrelated Han Chinese men from northeast China was 21.37%.

CONCLUSION

A novel mutation in the TBG gene associated with the TBG-CD phenotype was identified in a Chinese family. Additionally, it was found that 21.37% of Chinese males had TBG-Poly (L283F).

Keywords: Thyroxine-binding globulin, Complete thyroxine-binding globulin deficiency, Partial thyroxine-binding globulin deficiency, Gene polymorphism, Case report

Core tip: We present herein a novel thyroxine-binding globulin (TBG) mutation in exon 1, c.381_382 ins TTGCAGATAGGAAATGCCC (p.Phe135Alafs*21), which was associated with complete TGB deficiency in a Chinese family. This 19-nucleotide insertion in exon 1 resulted in a frameshift and a premature stop codon at position 155 of the protein coding sequence. TBG deficiency is often misdiagnosed as hypothyroidism. Clinical awareness is needed to correctly diagnose affected individuals and avoid unnecessary treatment. Genomic testing is a method to identify the mutation carriers and provide appropriate genetic counseling for affected individuals.