Familial dysalbuminemic hyperthyroxinemia combined with Graves' disease: a rare case report

BACKGROUND

Familial dysalbuminemic hyperthyroxinemia (FDH) is an autosomal dominant disease characterised by an abnormally increased affinity of albumin for serum thyroxine. Assay interference and differential diagnosis remain challenging for FDH. The condition is more complicated when FDH is combined with primary thyroid diseases. Co-occurrence of FDH and Graves' disease is rare.

CASE PRESENTATION

We report the case of a 28-year-old woman with complex FDH and coexisting Graves' disease. Initially, the existence of FDH was not recognised. Graves' disease was relieved after treatment with antithyroid drugs and two administrations of radioactive iodine therapy. She subsequently developed primary hypothyroidism and was prescribed levothyroxine replacement. However, thyroid function failed to normalise despite frequent levothyroxine dose adjustments. Ultimately, syndromes involving the inappropriate secretion of thyroid-stimulating hormone (IST) were considered, and FDH was successfully differentiated from other causes of IST.

CONCLUSIONS

A greater focus on FDH when investigating the causes of IST is critical to correctly evaluate thyroid function status and avoid inappropriate treatment, especially in complicated cases with concurrent FDH and primary thyroid diseases.

Clinical characteristics of familial dysalbuminemic hyperthyroxinemia in Chinese patients and comparison of free thyroxine in three immunoassay methods

OBJECTIVE

Familial dysalbuminemic hyperthyroxinemia (FDH) has not been thoroughly studied in the Chinese population to date. The clinical characteristics of FDH in Chinese patients were summarized, and the susceptibility of common free thyroxine (FT4) immunoassay methods was evaluated.

METHODS

The study included 16 affected patients from eight families with FDH admitted to the First Affiliated Hospital of Zhengzhou University. The published FDH patients of Chinese ethnicity were summarized. Clinical characteristics, genetic information, and thyroid function tests were analyzed. The ratio of FT4 to the upper limit of normal (FT4/ULN) in three test platforms was also compared in patients with R218H ALB mutation from our center.

RESULTS

The R218H ALB mutation was identified in seven families and the R218S in one family. The mean age of diagnosis was 38.4 ± 19.5 years. Half of the probands (4/8) were misdiagnosed as hyperthyroidism previously. The ratios of serum iodothyronine concentration to ULN in FDH patients with R218S were 8.05-9.74 for TT4, 0.68-1.28 for TT3, and 1.20-1.39 for rT3, respectively. The ratios in patients with R218H were 1.44 ± 0.15, 0.65 ± 0.14, and 0.77 ± 0.18, respectively. The FT4/ULN ratio detected using the Abbott I4000 SR platform was significantly lower than Roche Cobas e801 and Beckman UniCel Dxl 800 Access platforms (P < 0.05) in patients with R218H. In addition, nine Chinese families with FDH were retrieved from the literature, of which eight carried the R218H ALB mutation and one the R218S. The TT4/ULN of approximately 90% of patients (19/21) with R218H was 1.53 ± 0.31; the TT3/ULN of 52.4% of patients (11/21) was 1.49 ± 0.91. In the family with R218S, 45.5% of patients (5/11) underwent TT4 dilution test and the TT4/ULN was 11.70 ± 1.33 and 90.9% (10/11) received TT3 testing and the TT3/ULN was 0.39 ± 0.11.

CONCLUSIONS

Two ALB mutations, R218S and R218H, were found in eight Chinese families with FDH in this study, and the latter may be a high-frequency mutation in this population. The serum iodothyronine concentration varies with different mutation forms. The rank order of deviation in measured versus reference FT4 values by different immunoassays (lowest to highest) was Abbott < Roche < Beckman in the FDH patients with R218H.

Familial Dysalbuminemic Hyperthyroxinemia that was Inappropriately Treated with Thiamazole Due to Pseudo-thyrotoxic Symptoms

We herein report the case of a Japanese woman with familial dysalbuminemic hyperthyroxinemia (FDH) who was initially diagnosed with Graves' disease. Direct genomic sequencing revealed a guanine to cytosine transition in the second nucleotide of codon 218 in exon 7 of the albumin gene, which then caused a proline to arginine substitution. She was finally diagnosed with FDH, which did not require treatment. FDH is - superficially - an uncommon cause of syndrome of inappropriate secretion of thyrotropin (SITSH) in Japan. A misdiagnosis of pseudo-hyperthyroidism will lead to inappropriate treatment. Thus, physicians should strongly note the possibility of FDH as a differential diagnosis of SITSH.

A case of familial dysalbuminemic hyperthyroxinemia (FDH) in Japan: FDH as a possible differential diagnosis of syndrome of inappropriate secretion of thyroid-stimulating hormone (SITSH)

Familial dysalbuminemic hyperthyroxinemia (FDH) is an autosomal dominant condition and is the most commonly inherited euthyroid hyperthyroxinemia in Caucasians. However, it is extremely rare in Asian populations. A 30-year-old Japanese woman, who was incidentally found to have apparent thyroid dysfunction, was admitted to our hospital in 2004. She had extremely elevated serum free thyroxine (FT₄), moderately elevated free triiodothyronine (FT₃), and normal thyroid-stimulating hormone (TSH). Clinical thyroid examination revealed no abnormalities other than small goiter. Anti-thyroglobulin antibody titer was positive, but titers of other anti-thyroid antibodies, including antithyroid peroxidase antibody, TSH receptor antibodies, and thyroid-stimulating antibody, were negative. Levels of FT₃, FT₄, and TSH were similar when measured by three different laboratory kits, and FT₄ was still high when measured by equilibrium dialysis. By affinity chromatography, FT₄, TT₄, and albumin were extracted to the same fraction, and the levels of FT₄ and TT₄ were extremely high. By combination of reversed phase liquid chromatography and mass spectrometry techniques, the amino acid sequence of human serum albumin was determined. The patient was found to be a heterozygote for p.R218P mutation in the gene for human serum albumin and was diagnosed as FDH. This patient, who harbored the p.R218P mutation in the albumin gene, is the fifth case report of FDH in Japan. This condition is characterized by extremely high serum FT₄ and moderately high serum FT₃ levels. Although rare, FDH should be considered in the differential diagnosis for syndrome of inappropriate secretion of TSH (SITSH) in Japan.

Inherited defects of thyroxine-binding proteins

Thyroid hormones (TH) are bound to three major serum transport proteins, thyroxine-binding globulin (TBG), transthyretin (TTR) and human serum albumin (HSA). TBG has the strongest affinity for TH, whereas HSA is the most abundant protein in plasma. Individuals harboring genetic variations in TH transport proteins present with altered thyroid function tests, but are clinically euthyroid and do not require treatment. Clinical awareness and early recognition of these conditions are important to prevent unnecessary therapy with possible untoward effects. This review summarizes the gene, molecular structure and properties of these TH transport proteins and provides an overview of their inherited abnormalities, clinical presentation, genetic background and pathophysiologic mechanisms.

Familial dysalbuminemic hyperthyroxinemia in a 4-year-old girl with hyperactivity, palpitations and advanced dental age: how gold standard assays may be misleading

Here we report the case of a young girl who had vague signs and symptoms potentially attributable to hyperthyroidism and was found to have autoimmune thyroiditis and hyperthyroxinemia. The elevated serum free thyroxine levels were persistent when measured by both standard assays and equilibrium dialysis/high-pressure liquid chromatography-tandem mass spectrometry. The clinical symptoms, with discordant thyroid test results, created a diagnostic dilemma that led initially to unnecessary additional evaluations. She was ultimately found to have familial dysalbuminemic hyperthyroxinemia (FDH) and required no therapy. This case highlights the inherent difficulties in evaluating children, who typically have vague signs and symptoms of thyroid dysfunction, when, in addition, they have an unrelated acquired (autoimmune) as well as a genetic (FDH) defect. The benefit of including testing for immediate members of the family is emphasized.