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Eur Thyroid J. 2017 Jul;6(3):138-142. doi: 10.1159/000455097. Epub 2017 Feb 2.

A Novel Mutation in the TBG Gene Producing Partial Thyroxine-Binding Globulin Deficiency (Glencoe) Identified in 2 Families.

Author information

1
Department of Medicine, The University of Chicago, Chicago, IL, USA.
2
Department of Department of Endocrinology and Division of Laboratory Research, University Hospital Essen, University of Duisburg-Essen, Essen, Germany.
3
Department of Pediatrics, Feinberg School of Medicine Northwestern University, Chicago, IL, USA.
4
Department of Pediatrics, The University of Chicago, Chicago, IL, USA.
5
Department of Committee on Genetics, The University of Chicago, Chicago, IL, USA.

Abstract

BACKGROUND:

Thyroxine-binding globulin (TBG) is the major thyroid hormone transport protein in serum. Located on the long arm of the X chromosome, TBG (SERPINA7) gene mutations most commonly produce inherited partial TBG deficiency (TBG-PD).

OBJECTIVE:

We report a novel TBG variant associated with TBG-PD identified in 2 different families of Ashkenazi origin residing in greater Chicago.

METHODS:

Family 1: The proband was 12.6 years old when she presented for delayed puberty and was placed on L-T4. Although her serum TSH normalized, her serum T4 remained low. Affected family members had low total T4 and T3, but a normal free T4 index, even when serum TSH concentrations were normal. Family 2: A 71-year-old male presented with a history of a nonfunctioning pituitary adenoma and normal pituitary axes except for low total T4 and T3. His brother had a similar thyroid phenotype.

RESULTS:

Following direct DNA sequencing, both index patients were found to carry a missense mutation in the TBG gene (c.751T>G) producing p.V215G. The proposita of family 1 was heterozygous and the proband in family 2 was hemizygous for the mutation. Isoelectric focusing showed no alteration in the TBG isoforms and in vitro expression demonstrated a TBG with reduced affinity for T4.

CONCLUSIONS:

We report a novel mutation in the TBG gene in 2 unrelated families that produces a molecule with reduced affinity for T4 resulting in low serum T4. However, the physical properties of the mutant molecule remained unaltered as determined by isoelectric focusing.

KEYWORDS:

Mutation; T4-binding affinity; Thyroxine-binding globulin; Thyroxine-binding globulin deficiency

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