Thyroxine-binding Globulin Deficiency Research Articles

A-059 Evaluation of Free Thyroxin Levels in Patients with Low Thyroxin Binding Globulin Concentrations: Is There Interference in the FT4 Indirect Method?

Abstract Background Thyroxine-binding globulin (TBG) is the major carrier of thyroid hormones in serum. Variations in the serum concentration of TBG determine proportional variations in the total serum concentrations of T4 and T3, without implying changes in function, as long as the free fraction remains normal. Several common clinical conditions lead to significant alterations in TBG levels, the most important factor behind low levels being genetic defects. As TBG is encoded by a gene located on the X chromosome, the defects are more easily manifested in males. Differences in FT4 concentrations were observed in sera from subjects with TBG abnormalities, when FT4 are measured by different immunoassays, specially at extremes of TBG concentrations. The objective of this study was to evaluate FT4 levels by indirect method in patients with low TBG concentrations. Methods We analyzed blood samples requesting serum TBG, TSH and FT4 levels from patients admitted to a private reference clinical laboratory in Brazil, from January 01, 2017 to December 31, 2022. Anonymized data on laboratory tests was available from a database of the local Laboratory Information System. All the patients included had TSH within the reference range, 0.4–4.3 mUI/mL (ECLIA, Modular, Roche). FT4 was measured by ECLIA (0.7–1.8 ng/dL) and TBG by ICMA, Immulite, Siemens, 13–39 mcg/mL. Results 357 patients with low TBG levels were evaluated, 220 (62%) men, 137 (38%) women; mean age 35 yrs (19 d to 88 yrs). They were divided in six groups according TBG levels (mcg/mL): <3.5–17 (M 15, F2); 3.5 to 6.0 - 26 (M 20, F 6); 6.1 to 8.0 - 30 (M 25, F 5); 8.1 to 9.9 - 59 ( M 32, F 27); 10.0 to 11.9 - 139 (M 78, F 61); 12.0 to 12.9 - 86 (M 50, F 36). Three patients had FT4 levels above 1.8 (1.85; 1.87 and 1.96) ng/mL, all them male, with TBG levels <3.5; 5.79 and 9.53 ng/mL, respectively. Conclusion FT4 Indirect methods are developed taking into account the presence, in the serum, of a thyroxine binding capacity within the normal range, a fact that does not occur in individuals with extreme TBG deficiency. In this study, we found only one slightly elevated FT4 value among 17 patients with TBG values below 3.5 mcg/mL, suggesting little interference of very low TBG levels in this indirect free T4 method.

Partial Thyroid Hormone-Binding Globulin Deficiency: A Case Report and Literature Review.

Thyroxine binding globulin (TBG) deficiency is a rare thyroid disease, mostly caused by genetic mutations and acquired by X-linked recessive inheritance. The clinical features of children with TBG deficiency and their family members were summarised and the Serpina7 gene mutation was analysed, providing a reference for the differentiation of TBG deficiency. Thyroid function was detected in TBG deficient patients, and genetic analysis was performed using polymerase chain reaction (PCR) and direct DNA sequencing to detect the characteristics of TBG mutants. Using "thyroxine binding globulin, gene and mutation" as keywords, PubMed (biomedical literature database), Web of Science and other databases were searched for relevant studies to collect and summarise relevant information. The TBG (14.7 μg/mL), 70% triiodothyronine (T3) (<0.3 nmol/L), total T3 (Tr3) (<0.05 ng/mL) and thyroxine (T4) (14.72 nmol/L) values were lower than normal, while the thyrotropin (TSH) (2.33 uIU/mL), free T3 (FT3) (1.62 pmol/L), and free T4 (FT4) (11.39 pmol/L) values were normal. These values indicate a TBG partially deficient phenotype. Using PCR amplification and direct sequencing of the target gene, a missense mutation in exon 4 of the Serpina7 gene was found in the patient and the father, and the nucleic acid variant was C.909 (exon 4) g > T; the patient was heterozygous and the father was hemizygous. The literature search retrieved a total of 45 studies, most of which were related to mutations in the Serpina7 gene. The mutation locations included exons, introns, enhancers and promoters, with exons the predominant location. A total of 49 variants of the Serpina7 gene were identified. Serpina7 C.909G (P.L303F) is a mutation acquired from the father by X-linked recessive inheritance. The main clinical features of TBG deficiency patients are low serum T4, T3 and TBG levels, normal TSH, FT3 and FT4 levels, and no clinical manifestations.

Identification of Mutations in the Thyroxine-Binding Globulin (TBG) Gene in Patients with TBG Deficiency in Korea.

Thyroxine-binding globulin (TBG) is a major transporter protein for thyroid hormones. The serpin family A member 7 (SERPINA7) gene codes for TBG, and mutations of the SERPINA7 gene result in TBG deficiency. Although more than 40 mutations have been reported in several countries, only a few studies of TBG deficiency and SERPINA7 gene mutation have been performed in Korea. The aim of this study is to review the clinical presentations and laboratory findings of patients with TBG deficiency and to investigate the types of SERPINA7 gene mutation. Five unrelated Korean adults with TBG deficiency attending endocrinology clinic underwent SERPINA7 gene sequencing. Four patients harbored a SERPINA7 gene mutation. Serum thyroid hormones, anti-microsomal antibodies, and TBG were measured. Genomic DNA was extracted from whole blood. All exons and intron-exon boundaries of the TBG gene were amplified and sequencing was performed. Two patients were heterozygous females, and the other two were hemizygous males. One heterozygous female had coexisting hypothyroidism. The other heterozygous female was erroneously prescribed levothyroxine at a local clinic. One hemizygous male harbored a novel mutation, p.Phe269Cysfs*18, which caused TBG partial deficiency. Three patients had the p.Leu372Phefs*23 mutation, which is known as TBG-complete deficiency Japan (TBG-CDJ) and was also presented in previous mutation analyses in Korea. This study presents four patients diagnosed with TBG deficiency and provides the results of SERPINA7 gene sequencing. One novel mutation, p.Phe269Cysfs*18, causing TBD-partial deficiency and three cases of TBG-CDJ were demonstrated. It is necessary to identify TBG deficiency to prevent improper treatment. Also, sequencing of the SERPINA7 gene would provide valuable information about the TBG variants in Korea.

Identification of a novel mutation in thyroxine-binding globulin (TBG) gene associated with TBG-deficiency and its effect on the thyroid function.

This study presents a case of familial transmission of thyroxine-binding globulin (TBG) deficiency. The SERPINA7-gene which codes for TBG is located on the X-chromosome (Xq21-22). More than 45 mutations have been reported to cause TBG- deficiency from various countries, but none from India so far. Genetic analysis of SERPINA7 gene was carried out to determine the cause of low TBG levels in one family. DNA samples of the propositus and the family members were subjected to Polymerase Chain Reaction (PCR) followed by direct sequencing. Allele-specific PCR and Next-gen sequencing (NGS) were employed to confirm the site of the mutation. Thyroid function tests were estimated by Radioimmunoassay (RIA) and Immunoradiometric assay (IRMA) kits. X-chromosomal inactivation status was analyzed in the female members harboring the mutation. A mutational screening in this family revealed a novel frame-shift mutation S353Q, 354fs3X in the exon 4 ofthe SERPINA7gene which will be referred to as TBG-complete deficiency-India (TBG-CD-Ind). One out of four female family members harboring the mutation showed selective X-chromosomal inactivation. The affected family members were clinically euthyroid initially, showed changes in the thyroid function when tested after a long time span. However, the changes in the thyroid function in the affected family members had an autoimmune etiology. This study presents the first report of TBG-CD from India wherein a novel frameshift mutation referred to as TBG-CD-Ind (S353Q, 354fs3X)in the SERPINA7 gene was detected. No apparent association was identified between thyroid function and the TBG-mutation in the affected subjects. A detailed biochemical and genomic testing to determine the exact cause of discordant TFT in the patients would certainly aid in the unequivocal diagnosis of the thyroid function and for the precise individualized treatment.

The decrease of T3 / T4 is not hypothyroidism - a new mutation of Serpina7 gene results in partial thyroglobulin deficiency.

To explore an unusual cause of the decrease of T3/T4 through a new mutation of TBG gene in a family, so as to avoid habitual thinking and reduce subsequent over treatment. TSH, free total T4, T3 and free T4, T3 were determined by automatic chemiluminescence immunoassay. The TBG mutation was identified by direct DNA sequencing. A frameshift mutation of p. l372ffs * 32 was found in the TBG gene (c.1114delc) of the patient by direct DNA sequencing, and the proband of the family was heterozygous. In vitro expression showed that the affinity of TBG for T4 decreased. Further examination of the family members showed that T3 and T4 were decreased, while FT3, FT4 and TSH were normal. If the patients with low TT4 and TT3 but normal TSH are found, the serum TBG level and related genes should be detected to determine whether it is TBG deficiency and avoid wrong treatment.

Compound hemizygous variants in SERPINA7 gene cause thyroxine-binding globulin deficiency.

Sub‐headingCompound hemizygous variants in SERPINA7 gene.BackgroundThyroxine‐binding globulin (TBG) is encoded by SERPINA7 (OMIM. 314200) which is located on Xq22.3. SERPINA7 variants caused TBG deficiency which does not require treatment, but the decreased thyroxine may be misdiagnosed as hypothyroidism. We discovered some variants of TBG caused by alterations that differ from previously reported.Materials and MethodsIn this study, we enrolled 32 subjects from 10 families and sequenced the SERPINA7 genes of TBG‐deficient subjects. Then, variants were analyzed to assess their effect on TBG expression and secretion. Bioinformatics database, protein structure, and dynamics simulation were used to evaluate the deleterious effects. Finally, we identified 2 novel and 4 known variants, and found 26 of 30 subjects carried the p.L303F. The DynaMut predictions indicated the variants (p.E91K, p.I92T, p.R294C, and p.L303F) exhibited decreased stability.ConclusionAnalyses revealed the p.L303F change the protein stability and flexibility, and it had an impact on the function of TBG, but when coexisted with other variants it might change the conformational structure of the protein and aggravate the damage to the protein. We speculated that the existence of a higher number of variants resulted in lower TBG secretion.

Thyroxine-binding globulin deficiency due to a novel SERPINA7 mutation: Clinical characterization, analysis of X-chromosome inactivation pattern and protein structural modeling

ObjectiveThyroxine-binding globulin (TBG) is the major human thyroid hormone transport protein, encoded by the SERPINA7 gene (Xq22.2). We aim to investigate the molecular basis of partial TBG deficiency (TBG-PD) in a female, by evaluating the X-chromosome inactivation pattern as well as the mutant protein structural modeling. Design and methodsSequencing of the coding region of the SERPINA7 gene was performed in a female with a TBG-PD phenotype and her first-degree relatives. The proband presented with low serum levels of total T3 (TT3) and total T4 (TT4), serum TSH level of 5.4 μUI/mL (normal range, 0.35–5.5), and serum TBG level of 5.5 mg/L (normal range, 13.6–27.2). X-chromosome inactivation pattern was evaluated by methylation analysis of the androgen receptor gene (Xq11.2). Structural analysis of the SERPIN family was performed using Pymol and Areaimol, and PFSTATS for conservation analysis and family-wide investigation of equivalent positions in human homologs. Modeller was used for point mutation structural modeling. ResultsA novel missense SERPINA7 mutation (p.R35W; c.163C > T) was found in heterozygosity in the proband, and in hemizygosity in her affected siblings. The proband X-chromosome inactivation ratio was 20:80. The substitution of an arginine by a tryptophan is predicted to disrupt the protein surface and main electrostatic interactions. Tryptophans are extremely rare (0.1%) in this position. ConclusionsWe report a new SERPINA7 variant associated with TBG-PD in three siblings. We named this variant TBG-Brasilia. The X-chromosome inactivation pattern may have accounted for the rare phenotypic expression in a female. The hydrophobic nature of the mutant is predicted to create an apolar patch at the surface, which results in protein aggregation and/or misfolding, potentially responsible for thyroid hormone transport defect.

Detecting Congenital Central Hypothyroidism by Newborn Screening: Difficulty in Distinguishing from Congenital Thyroxine-Binding Globulin Deficiency

Background/Aims: Congenital central hypothyroidism (CH-C) can be detected on newborn screening (NBS) by programs using thyroxine (T4)-reflex thyroid-stimulating hormone (TSH) test approach. CH-C must be distinguished from T4-binding globulin (TBG) deficiency. We sought to determine whether thyroid function tests reliably separate CH-C from TBG deficiency. Methods: We analyzed NBS and serum free and total T4, T3 resin uptake (T3RU) or TBG, and TSH for infants in the Northwest Regional NBS Program (NWRSP) between the years 2008 and 2015 with either CH-C or TBG deficiency. Results: We discovered a significant overlap in T3RU and TBG levels amongst 21 cases of CH-C and 250 cases of TBG deficiency. Mean serum TBG levels were lower in CH-C cases (20.3 µg/mL, range 14.2–33.3) than what is reported in healthy infants (28.6 µg/mL, range 19.1–44.6). Serum free T4 was lower in CH-C cases than TBG deficiency but did not always differentiate between the two conditions. Conclusion: CH-C benefits from detection on NBS but must be distinguished from TBG deficiency. The diagnosis of CH-C rests solely on subnormal serum free T4, but is supported by the demonstration of other pituitary hormone deficiencies. As an overlap exists, serum TBG (or T3RU) levels do not play a role in the diagnosis of CH-C.

A novel variant in the SERPINA7 gene causing partial TBG deficiency in a women and two male siblings: molecular and protein structural analysis

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Directional thyroid hormone distribution via the blood stream to target sites

Thyroid hormones are bound to three major serum transport proteins, thyroxin-binding globulin (TBG), transthyretin (TTR) and human serum albumin (HSA). TBG has the strongest affinity for thyroid hormones, TTR is also found in the cerebrospinal fluid and HSA is the most abundant protein in plasma. Combination defects of either a high affinity TTR or HSA variant do not compensate TBG deficiency, underscoring the dominant role of TBG among the thyroid hormone transport proteins. On the other hand, coexistence of raised affinity TTR and HSA variants causes an augmented hyperthyroxinemia. Variations in thyroid hormone transport proteins may alter thyroid function tests to mimic hypo- or hyperthyroidism. As affected individuals are clinically euthyroid and do not require treatment, identification of thyroid hormone transport protein defects is important to avoid unnecessary diagnostic and therapeutic interventions. Mammals share the multilayered system of thyroid hormone binding proteins with humans. Some of them, especially carnivores, do not express TBG. In dogs, this defect has been shown to be caused by a defective hepatocyte nuclear factor-1 binding site in the TBG promoter, preventing TBG synthesis in the liver. The major endogenous thyroid hormone metabolite 3-iodothyronamine (3-T1AM) exerts marked cryogenic, metabolic, cardiac and central nervous system actions. It is bound to apolipoproteinB-100 (ApoB100), possibly facilitating its cellular uptake via interaction with the low density lipoprotein-receptor. This review summarizes the handling of hydrophobic charged thyroid hormone signaling molecules and their metabolite 3-T1AM in aqueous body fluids and the advantages and limits of their serum distributor proteins.

A Novel Mutation Causing Complete Thyroid Binding Globulin Deficiency (Tbg-Cd Mia) In A Male With Coexisting Graves Disease

An asymptomatic male was found on screening to have a low serum TSH and total T4. The diagnosis of Graves' disease was made with positive thyroid stimulating immunoglobulin (TSI) and elevated free T4 in the presence of complete TBG deficiency (TBG-CD). Genetic testing of the patient and family members revealed a novel frameshift mutation in the TBG (SERPINA7) gene resulting in a complete deficiency of the protein. The laboratory testing included total T4, free T4 by analog method and direct dialysis and TBG measurements. Sequencing of genomic DNA was performed from peripheral blood. A 35-year-old East Indian male was referred to endocrinology because of abnormal thyroid function tests (TFTs): TSH 0.01 mIU/L (0.4-3.6), total T4 3.0 µg/dl (5.5-10.5) done as part of a "routine office visit". Upon further testing, the serum free T4 2.0 ng/dl (0.8-1.8) and TSI 355% (<140% baseline) were elevated and the diagnosis of Graves' disease was made. TBG deficiency was suspected because the total T4 concentration was inconsistent with hyperthyroidism and further testing confirmed TBG was undetectable. Sequencing of the TBG gene revealed a novel hemizygous frameshift mutation: p.Ala64ProfsTer106, TBG-CD Mia (numbering excludes 20 a.a. signal peptide) associated with the complete deficiency of TBG in a patient with Graves' disease. Patients with Graves' disease harboring a TBG mutation have conflicting TFTs. If a clinically hyperthyroid patient presents with normal or low total T4, serum TBG should be measured to identify an abnormality and prevent unnecessary testing.

Thyroxin-binding globulin deficiency in a boy with fragile X syndrome: a case report

Fragile X syndrome (FXS) is the most common known genetic cause of male intellectual disability. A wide variety of medical problems has been reported in FXS syndrome including seizures, facial abnormalities, macroorchidism, and autistic disorders. Here we reported a 9-year-old boy with fragile X syndrome that was confirmed through karyotyping and mental retardation. Initially, he was diagnosed as hypothyroidism when he was 15 months old. However, due to unusual clinical presentation, we re-evaluated the patient according to his history and clinical findings. Subsequently, targeted laboratory tests were performed and the results were indicative for thyroxin-binding globulin (TBG) deficiency in our patient. Therefore, levothyroxine was discontinued and one month later, laboratory tests were repeated and his diagnosis confirmed. As inherited TBG deficiency might also be X-linked, FXS and TBG deficiency may be coincidental findings in the patient.

Thyroxine binding globulin excess detected by neonatal screening.

Inherited thyroxine binding globulin (TBG) disorder can be identified incidentally or through neonatal screening test. TBG excess is characterized by high levels of thyroxine (T4) but normal level of free T4 (fT4), while TBG deficiency presents with low T4 levels and normal fT4 levels. A 27-day-old newborn was brought to the hospital because of hyperthyroxinemia detected by neonatal screening. His T4 level was 18.83 µg/dL (normal range, 5.9–16.0 µg/dL). His mother had no history of any thyroid disease. His fT4 and thyroid stimulating hormone (TSH) levels were 1.99 ng/dL (normal range, 0.8–2.1 ng/dL) and 4.54 mIU/L (normal range, 0.5–6.5 mIU/L), respectively. His serum total triiodothyronine (T3) level was 322.5 ng/dL (normal range, 105.0–245.0 ng/dL). His TBG level was 68.27 mg/L (normal range, 16.0–36.0 mg/L) at the age of 3 months. At 6 months and 12 months of age, his TBG levels were 48.77 mg/L (normal range, 16.0–36.0 mg/L) and 50.20 mg/L (normal range, 14.0–28.0 mg/L), respectively, which were 2 to 3 times higher than normal values. Hormonal studies showed consistently elevated T3 and T4 levels and upper normal levels of fT4 and free T3 with normal TSH levels. His growth and development were normal. TBG excess should be considered as a potential differential diagnosis for hyperthyroxinemia and especially high T3 levels with normal TSH concentration.

A Study of Thyroid Function in Partial Thyroxine-Binding Globulin Deficiency

Objective: It is generally thought that thyroxine-binding globulin (TBG)-deficient individuals are euthyroid and do not require treatment. However, there have been case reports of TBG deficiency combined with hypothyroidism. The purpose of this study was to investigate the relationship between TBG deficiency and thyroid function. Methods: We reviewed the medical records of 32 patients diagnosed with TBG deficiency between 1997 and 2008 in Soonchunhyang University Seoul Hospital. All were partial TBG deficiency. Eighteen patients had combined hypothyroidism, and 14 patients had normal thyroid function. We compared the TBG, thyroid-stimulating hormone, free thyroxine, and total triiodothyronine levels between these 2 groups. Eighteen patients with TBG deficiency with hypothyroidism started thyroxine medication and continued for 2-3 years. After, they were followed up with thyroid function tests after discontinuing medication for 4 weeks at 2-3 years of age. Results: The TBG level in TBG deficiency with hypothyroidism patients was significantly lower than that in TBG deficiency with normal thyroid function (4.43± 2.22 mg/L vs. 6.23± 1.81 mg/L; P= 0.02). The percent TBG compared with normal mean TBG level according to age in the hypothyroidism patients was also significantly lower than that of patients with normal thyroid function (13.42%± 6.92% vs. 19.08%± 4.87%; P= 0.014). Sixteen of 18 patients diagnosed with TBG deficiency with hypothyroidism showed persistent hypothyroidism at 2-3 years of age. Conclusion: We conclude that TBG-deficient patients should be observed closely and undergo thyroid function testing in order not to miss hypothyroidism. More investigations of TBG deficiency and thyroid function are needed in the future.

Novel Mutation p.A64D in the Serpina7 Gene as a Cause of Partial Thyroxine-binding Globulin Deficiency Associated with Increases Affinity in Transthyretin by a Known p.A109T Mutation in the TTR Gene

Partial thyroxine-binding globulin deficiency (TBG-PD) is an endocrine defect with a prevalence of 1:4 000 in newborns. Due to the presence of a single TBG gene on the X chromosome, most familial TBG defects follow an X-linked inheritance pattern. Abnormal T4 binding to T4-binding prealbumin (TTR) is a rare cause of euthyroid hyperthyroxinemia, which is transmitted by autosomal dominant inheritance. The purpose of the present study was to identify and characterize new mutations in the Serpina7 and TTR genes in a complete family with typical TBG-PD. All patients underwent clinical and biochemical evaluation. Sequencing of DNA, population screening by (SSCP) analysis, and bioinformatics studies were performed. Molecular studies revealed a novel p.A64D mutation in the exon 1 of Serpina7 gene associated with the previously reported p.A109T mutation in the exon 4 of TTR gene. To our knowledge, this is the first report of a patient with a TBG-PD by a mutation in Serpina7 that was coincident with a mutation in TTR gene that increased affinity of TTR for T4. This work contributes to elucidate the molecular basis of the defects of thyroid hormone transport in serum and the improvement of the diagnosis avoiding unnecessary therapy.

Rare thyroid diseases

In general, rare thyroid diseases can be divided into neoplastic and non-neoplastic. Neoplastic rare thyroid diseases include the following: 1. primary thyroid lymphoma (1-5% all malignant neoplasms of the thyroid; 2:1 000 000 per year); 2. metastases to the thyroid gland (2-3% malignant thyroid neoplasms; 0.5-2.8% in autopsy) from various primary cancers such as breast carcinoma, renal carcinoma, colon carcinoma, melanoma and others; 3. others (ie: sarcoma). On the contrary, non-neoplastic rare thyroid diseases include the following: 1. congenital defects of thyroxine binding proteins, particularly partial and total congenital TBG deficiency (1:5 000), congenital TBG excess (1: 25 000) (both caused by TBG gene mutations) and familial dysalbuminemic hyperthyroxinemia (1:25 000, more frequent in some populations, such as the Spanish and Portuguese); 2. congenital resistance to thyroid hormones (with frequency about 1:40 000) as a result of THRB gene mutations; 3. rare cases of congenital thyroid hormones biosynthesis defects, for instance: Pendred syndrome (with frequency of 7.5-10:100 000) resulting from PDS gene mutations, total iodide organification defects (1:66 000; TPO and THOX2 gene mutations); 4. congenital defects of the thyroid gland development, which constitute about 85-90% causes of primary congenital hypothyroidism. About 2% of these are associated with the presence of other nonthyroid congenital anomalies and are caused by genetic mutations: for example, in the PAX, TTF1, TTF2, GNAS 1 genes; 5. congenital nonautoimmune hyperthyroidism as a result of TSH receptor gene mutation (TSHR) (until now 55 various mutations and over a dozen cases of de novo germinal mutations have been described); 6. hyperthyroidism associated with McCune-Albright syndrome (in about 30% of patients with this syndrome; McCune-Albright syndrome frequency of occurrence is estimated - 1:10 000-1:1 000 000; background - mutation in the GNAS 1 gene); 7. an association of the thyroid autonomous nodule and Graves’ disease (4.1%), and the thyroid cancer and Graves’ disease (1.1%-6.5%). The latest data on the etiopathogenesis of rare thyroid diseases, diagnostic criteria and possibilities for their treatment will be discussed. In addition, information obtained from PUBMED database concerning patients with rare thyroid diseases detected in the Polish population, particularly the data on molecular-genetic results, will be presented.

A Case of Hypothyroxinemia with Thyroxine-Binding-Globulin Deficiency

The transport proteins such as thyroxine-binding-globulin (TBG), albumin and transthyretin carry over 99% of circulating thyroid hormones. TBG is a major thyroid hormone transport protein in serum. Although TBG deficiency does not have metabolic conse quences, it has diagnostic implications as it can lead to an incorrect interpretation of thyroid function tests. We experienced a case that a man who had an abnormal thyroid function showed unexpectedly low concentrations of serum total thyroxine. We detected the low TBG in his serum and he was diagnosed the TBG deficiency. We report this case along with a review of the related literature.

Diagnostic and therapeutic confusion caused by TBG deficiency in an 18 years old adolescent

Diagnostic and therapeutic confusion caused by TBG deficiency in an 18 years old adolescent

A novel variant in Serpina7 gene in a family with thyroxine-binding globulin deficiency

Thyroxine-binding globulin (TBG) carries approximately 75% of serum T4 and T3. This protein is encoded by serpina7 gene, formerly known as TBG gene, localized on X-chromosome (Xq22.2). A deficiency in TBG is suspected when abnormally low serum total T4 and T3 are encountered in clinically euthyroid subjects in the presence of normal serum TSH. This condition has been associated with different serpina7 gene mutations resulting in amino acid substitutions or truncations in the mature protein. Herein, we report a new serpina7 gene variant in three members of the same family. It results in the replacement of the normal asparagine 233 by isoleucine and, subsequently, in disruption of a glycosylation site. Co-segregation of this new variant with undetectable levels of TBG in the hemizygous man studied and failure to recognize the same variant in 100 alleles at random, made us to consider it as the underlying cause of the TBG deficiency.

Diagnostic problems of hyperthyroidism in the older age group (author's transl)

Seventy-seven patients aged more than 60 years from the iodine deficiency area of southern Lower Saxony with hyperthyroidism, diagnosed by assessment of thyroid parameters, showed a nonspecific disease picture with surprising frequency when compared with younger patients. Predominant characteristics were weight loss (86%), general weakness (78%), tachycardia (74%), reduced appetite (66%), exertional dyspnoea (60%), apathy, lack of initiative or depression (48%), and uncharacteristic abdominal complaints (20%). A goitre was not palpable in 30 patients (39%). Laboratory diagnosis was hampered by relative or absolute TBG deficiency and conversion inhibition in the form of a low-T3 syndrome as evidence of non-thyroidal changes in generalised disorders. Neither thyroxine nor triiodothyronine were increased in ten patients (13%). Only by additional routine estimation of the thyroxine-binding index (T3 in vitro test) as indicator of free binding capacity could the diagnosis be ascertained in these cases. The poor prognosis be ascertained in these cases. The poor prognosis of hyperthyroidism in the older age group necessitates generous use of specific diagnostic laboratory investigations in cases with suspicious symptoms.