1/38. A point mutation in the albumin gene in a Chinese patient with familial dysalbuminemic hyperthyroxinemia. Familial dysalbuminemic hyperthyroxinemia (FDH) is an autosomal dominant disorder characterized by euthyroid hyperthyroxinemia. However, FDH has not been reported in Chinese or African patients. Here, we report the first case of FDH in a Chinese patient. A 69-year-old Chinese man was found to have increased serum total T(4) concentrations (198-242nmol/l; normal range 58-148nmol/l) and free T(4) concentrations (>58pmol/l; T(4) analog method, normal range 9-28pmol/l). Serum total T(3) and TSH concentrations were normal. The patient was misdiagnosed as hyperthyroid and was later suspected to have a TSH-producing tumor by the finding of a pituitary microadenoma, which was eventually proven to be a non-functional pituitary 'incidentaloma'. Electrophoretic analysis of the patient's serum proteins demonstrated enhanced albumin binding of [(125)I]T(4). Serum free T(4) concentrations were normal (16-19pmol/l, normal range 9-26pmol/l) when a two-step method was used. Direct sequencing of the albumin gene showed a guanine to adenosine transition in the second nucleotide of codon 218, resulting in a substitution of histidine (CAC) for the normal arginine (CGC) in one of the two alleles in the patient. The point mutation was further confirmed by HphI digestion of exon 7 of the albumin gene. The patient's son was not affected. Our studies demonstrated that the point mutation of the albumin gene in a Chinese patient with FDH was similar to that found in western white families, but differed from that in a Japanese family in whom a guanine to cytosine transition at the same position was found. ( info) |
2/38. Familial dysalbuminemic hyperthyroxinemia in a Swiss family caused by a mutant albumin (R218P) shows an apparent discrepancy between serum concentration and affinity for thyroxine. Familial dysalbuminemic hyperthyroxinemia (FDH), is the most common cause of inherited increase in serum total T4 (TT4) in the Caucasian population. It is caused by a mutation (R218H) in the human serum albumin (HSA) gene, resulting in 10-fold higher affinity for T4 and, in heterozygous affected subjects, a TT4 level 2-fold higher than that in subjects expressing the wild-type HSA only. We now report FDH in a Swiss family, caused by HSA R218P, previously reported in subjects of Japanese origin. In this form of FDH, serum TT4 levels are 14- to 20-fold the normal mean, confirmed by measurements in serum extracts. TrT3 and TT3, concentrations are 7- and 2-fold above the mean, respectively. Thus, to maintain a normal free T4 level, the calculated affinity constant (Ka) of HSA R218P should be about 16-fold higher than that of HSA R218H. Surprisingly, the Ka values measured at saturation were similar: 5.4 x 10(6) and 6.4 x 10(6) mol/L(-1) for HSA R218H, respectively. To determine how subjects with HSA R218P and R218P maintain a euthyroid state despite the markedly high serum TT4, the concentration of dialyzable T4 was measured at increasing amounts of TT4. At a TT4 level equivalent to that found in the subjects with HSA R218P, the absolute FT4 concentrations were 40, 432, and 1970 pmol/L for sera expressing HSAs R218P, R218H, and wild type, respectively. Thus, the affinity of HSA R218P for T4 must be higher than that of R218H to produce an 11-fold difference in FT4 at the same concentration ofTT4 This difference was obliterated at saturating concentrations of TT4 used for the determination of Ka values by the method of Scatchard. ( info) |
| We describe a case of euthyroid hyperthyroxinemia in whom clinical and laboratory investigations strongly supported the diagnosis of generalised thyroid hormone resistance. ( info) |
4/38. Abnormal serum free thyroid hormone levels due to heparin administration. Fractionated or unfractionated heparin may produce artefactual elevation in measured concentrations of free thyroid hormones. Although the specific cause is unknown, it may be a consequence of displacement of thyroid hormones from their binding sites by free fatty acids liberated in vitro. We describe four cases of heparin-induced abnormalities in free thyroid hormone measurements where some diagnostic confusion was generated. Increasing physician awareness of this poorly appreciated entity may avert diagnostic confusion and unnecessary investigation. ( info) |
5/38. congenital hypothyroidism in a child with unsuspected familial dysalbuminemic hyperthyroxinemia caused by a mutation (R218H) in the human albumin gene. We found familial dysalbuminemic hyperthyroxinemia (FDH) in a 5-month-old boy with congenital hypothyroidism (CH) who had a blood thyrotropin (TSH) level of 479 mU/L but normal total serum thyroxine (T4) and higher than normal total triiodothyronine (T3) levels. Thyroid hormone substitution began at 5 weeks of age when T4 and T3 concentrations were below normal. Until the age of 5 months, treatment with levothyroxine was suboptimal on the basis of high serum TSH levels despite above-normal T4 levels. FDH was confirmed by isoelectric focusing and testing of other family members. dna analysis of the patient revealed R218H, a mutation in the serum albumin gene associated with FDH, which was also present in the patient's euthyroid father and brother. Thyroid scans, serum thyroglobulin measurements, and free T4 measurements using equilibrium dialysis or 2-step immunoassay methods can identify thyroid hormone-binding protein defects and simplify the diagnosis and treatment of infants with CH. ( info) |
6/38. Detection of albumin binding abnormalities in sera of patients with familial dysalbuminaemic hyperthyroxinaemia using isoelectric focusing. Definitive diagnosis of familial dysalbuminaemic hyperthyroxinaemia (FDH) requires finding a high concentration of [125I]T4 bound to albumin. We used isoelectric focusing (IEF) in agarose gels to study the sera of three members of a family with FDH and compared the distribution of [125I]T4 obtained by IEF with that obtained by conventional agarose gel electrophoresis (AGE). Both IEF and AGE confirmed the diagnoses of FDH. In case #1, the % [125I]T4 bound to albumin was 15.2 and 20.0, with IEF and AGE, respectively, in case #2 23.6 and 26.5, and in case #3, 22.1 and 23.0, compared to normal controls of 5.9 and 7.4, respectively. IEF has not previously been used to diagnose FDH, to our knowledge. IEF has the advantage of eliminating TBG interference with albumin migration, which can potentially complicate the diagnosis of FDH when the AGE method is used. To date, reverse flow electrophoresis, a more cumbersome method with poorer resolution than IEF, has been utilized to eliminate TBG interference. IEF, in agarose gels, is a relatively simple and accurate method to diagnose FDH, and avoids artifacts which may be encountered with AGE. ( info) |
7/38. A Chinese family with familial dysalbuminaemic hyperthyroxinaemia. We report the results of biochemical and genetic studies in a Chinese family with familial dysalbuminaemic hyperthyroxinaemia. Total thyroxine levels were 1.2 to 1.7 times the upper limit of the reference range and free thyroxine levels were 1.2 to 1.6 times the upper reference limit. Concentrations of thyroid-stimulating hormone (thyrotropin) and free tri-iodothyronine were normal in all family members tested. overall, thyroid function tests showed high total thyroxine levels in five males and two females over two generations in the family. The diagnosis of familial dysalbuminaemic hyperthyroxinaemia was confirmed by the detection of a guanine to adenine missense mutation in the second nucleotide of codon 218 of the gene encoding human serum albumin, showing that the mutation in this family is the same as that previously found in Caucasian populations. ( info) |
8/38. Artifactually elevated serum-free thyroxine levels measured by equilibrium dialysis in a pregnant woman with familial dysalbuminemic hyperthyroxinemia. Familial dysalbuminemic hyperthyroxinemia (FDH) is a familial autosomal dominant syndrome caused by abnormal albumin with an increased affinity for thyroxine (T4). Two types of mutations in the albumin gene, replacing the normal arginine 218 with a histidine (R218H) or a proline (R218P), have been reported to cause FDH. Here, we report a pregnant Japanese woman with FDH caused by the mutant albumin R218P. She had extremely elevated total T4 levels but normal TSH. While the majority of T4was bound to albumin, T4 binding to thyroxine-binding globulin (TBG) was progressively increased throughout pregnancy. Her infant also had elevated serum T4 but normal thyrotropin (TSH). The presence of a guanine to cytosine transition in the second nucleotide of codon 218 of the albumin gene, resulting in a substitution of proline for the normal arginine (R218P), was revealed in the proband. Serum free thyroxine (FT4) levels were increased when measured with some commercial kits including equilibrium dialysis followed by radioimmunoassay (RIA) but not when determined by RIA after ultrafiltration of sera. These results indicate an increased T4 binding to TBG during pregnancy in the patients with FDH. Furthermore, our results suggest that normal serum FT4 determined by equilibrium dialysis is not an ultimate standard for the diagnosis of FDH in the patients with the mutant albumin R218P. ( info) |
| Rare mutant forms of circulating albumin and prealbumin [transthyretin (TTR)] have increased binding affinity for thyroxine (T4). patients with these variant plasma proteins, as a result of inherited mutations or as a paraneoplastic phenomenon, typically present with increased serum total T4 and, by some assay methodologies, an increased free T4 as well. Although these individuals are, in fact, euthyroid, nonspecific symptoms may lead to inappropriate treatment for hyperthyroidism. We present a 34-year-old woman in whom a mutant form of TTR with increased T4 binding affinity and coexisting graves disease was present. Subsequent 131I therapy led to development of postablative hypothyroidism, which was obscured by her higher serum free T4 concentration. Circulating thyroid-binding globulin (TBG), albumin, and TTR concentrations were all within their respective reference limits. A T4-binding protein panel confirmed that TTR-bound T4 was significantly increased, whereas TBG- and albumin-bound T4 was normal, indicating that this patient had euthyroid dysprealbuminemic hyperthyroxinemia, which had been masked by the initial presentation of hyperthyroidism. These findings indicate that hypothyroidism can be masked by coexisting euthyroid dysprealbuminemic hyperthyroxinemia. ( info) |
10/38. Familial dysalbuminemic hyperthyroxinemia associated with multinodular goiter and elevated radioiodine uptake. A case report. Familial dysalbumenic hyperthyroxenemia characterized by elevations in serum total thyroxine (T4) and free-thyroxine index and normal free T4 and radioiodine uptake has been previously described. This syndrome is secondary to an autosomal dominant inheritance in which affected individuals are mistakenly diagnosed as thyrotoxic because of the elevation of serum levels of total T4 and free T4. The excess T4 level is caused by the presence of an abnormal serum protein that binds excess T4, thereby raising the level of total T4. The authors report the case of a patient with familial dysalbumenic hyperthyroxenemia who presented with superimposed multinodular goiter and an elevated 24-hour radioiodide uptake. ( info) |