[Association analysis of PDE8B gene polymorphisms with the susceptibility to Hyperthyroxinemia in Chinese Han population].

OBJECTIVE: To explore the correlations of the polymorphisms of phosphodiesterase 8B (PDE8B) gene with Hyperthyroxinemia in Chinese Han population. METHODS: A case-control study of genotype 657366 SNPs was performed by Illumina Human660-Quad BeadChips in 98 Hyperthyroxinemia patients and 1300 controls. And 25 SNPs within PDE8B gene intron 1 were used for association analyses. RESULTS: Allele frequencies of 5 SNPS in PDE8B gene intron 1 showed significant differences between the case and control groups (P < 0.05). In comparison with the control group, the genotypic distributions of rs7714529 (χ(2) = 6.430, P = 0.040), rs12514694 (χ(2) = 7.191, P = 0.027) and rs10066802 (χ(2) = 9.213, P = 0.010) in H-TSH group had significant differences. Haplotype AGTAG (rs7702192/rs7714529/rs251421/rs12514694/rs10066802) was over-represented in hyperthyrotropinemia cases versus the control group. CONCLUSION: PDE8B gene polymorphisms may be correlated with Hyperthyroxinemia in Chinese Han population. And it may provide new concepts for the treatment of thyroid dysfunction.

Update on Neonatal Isolated Hyperthyrotropinemia: A Systematic Review.

The purpose of this paper was to systematically summarize the published literature on neonatal isolated hyperthyrotropinemia (HTT), with a focus on prevalence, L-T4 management, re-evaluation of thyroid function during infancy or childhood, etiology including genetic variation, thyroid imaging tests, and developmental outcome. Electronic and manual searches were conducted for relevant publications, and a total of 46 articles were included in this systematic review. The overall prevalence of neonatal HTT was estimated at 0.06%. The occurrence of abnormal imaging tests was found to be higher in the persistent than in the transient condition. A continuous spectrum of thyroid impairment severity can occur because of genetic factors, environmental factors, or a combination of the two. Excessive or insufficient iodine levels were found in 46% and 16% of infants, respectively. Thirty-five different genetic variants have been found in three genes in 37 patients with neonatal HTT of different ethnic backgrounds extracted from studies with variable design. In general, genetic variants reported in the TSHR gene, the most auspicious candidate gene for HTT, may explain the phenotype of the patients. Many practitioners elect to treat infants with HTT to prevent any possible adverse developmental effects. Most patients with thyroid abnormalities and/or carrying monoallelic or biallelic genetic variants have received L-T4 treatment. For all those neonates on treatment with L-T4, it is essential to ensure follow-up until 2 or 3 years of age and to conduct medically supervised trial-off therapy when warranted. TSH levels were found to be elevated following cessation of therapy in 44% of children. Withdrawal of treatment was judged as unsuccessful, and medication was restarted, in 78% of cases. Finally, data extracted from nine studies showed that none of the 94 included patients proved to have a poor developmental outcome (0/94). Among subjects presenting with normal cognitive performance, 82% of cases have received L-T4 therapy. Until now, the precise neurodevelopmental risks posed by mild disease remain uncertain.

Role of serum carrier proteins in the peripheral metabolism and tissue distribution of thyroid hormones in familial dysalbuminemic hyperthyroxinemia and congenital elevation of thyroxine-binding globulin.

To investigate the role of thyroxine-binding globulin (TBG) and albumin in the availability of thyroid hormones to peripheral tissues, comprehensive kinetic studies of thyroxine (T4) and triiodothyronine (T3) were carried out in eight subjects with familial dysalbuminemic hyperthyroxinemia (FDH), in four subjects with inherited TBG excess, and in 15 normals. In high-TBG subjects, the reduction of T4 and T3 plasma clearance rates (by 51% and 54%, respectively) was associated with normal daily productions; T4 and T3 distribution volumes were significantly reduced. In FDH subjects T4 clearance was less reduced (by 31%) than in high TBG; consequently T4 production rate was significantly increased (by 42%); T4 and T3 distribution volumes and T3 clearance rate were unchanged. Increased T3 peripheral production in FDH (by 24%) indicates that T4 bound to abnormal albumin is more available to tissues than T4 carried by TBG, thus suggesting an important role of albumin in T4 availability to the periphery.

Transthyretin mutations in hyperthyroxinemia and amyloid diseases.

Over 80 different disease-causing mutations in transthyretin (TTR) have been reported. The vast majority are inherited in an autosomal dominant manner and are related to amyloid deposition, affecting predominantly peripheral nerve and/or the heart. A small portion of TTR mutations are apparently non-amyloidogenic. Among these are mutations responsible for hyperthyroxinemia, presenting high affinity for thyroxine (a TTR ligand). Compound heterozygotic individuals for TTR mutants have been described; noteworthy is the clinically protective effect exerted by a non-pathogenic over a pathogenic mutation. Current TTR mutations and their significance are briefly reviewed here.

Hyperthyroxinemia due to the coexistence of two raised affinity thyroxine-binding proteins (albumin and prealbumin) in one family.

The T4-binding proteins of a euthyroid subject with persistent hyperthyroxinemia (T4, greater than 20 micrograms/dl) were present in normal concentrations. Abnormal transport of both T4 and rT3 was demonstrated by reverse flow paper electrophoresis; excess T4 was bound to albumin and prealbumin, while increased binding of rT3 was confined to prealbumin. The three T4-binding proteins in the serum of the subject were isolated by affinity chromatography and characterized. Equilibrium dialysis experiments demonstrated a 20-fold increase in affinity of the albumin for T4 (Ka, 5.1 X 10(6) M-1) and a 4-fold increase in affinity of prealbumin for T4 (Ka, 3.0 X 10(8) M-1); T4-binding globulin affinity was normal. Nine other members of the family were also studied. Two sisters of the propositus have both the abnormal albumin and the variant prealbumin, while a brother has normal T4-binding proteins. The mother has the abnormal albumin alone. The father, his sister, and one of his three brothers have the variant prealbumin only. Despite the presence of the variant prealbumin in some of the paternal relatives of the propositus, their total iodothyronine concentrations were within the normal ranges; the condition may, therefore, often go undetected. The characteristics of the albumin found in the affected members of this kindred are those we have defined for familial dysalbuminemic hyperthyroxinemia type I, which is inherited as an autosomal dominant trait. The pattern of inheritance of the variant prealbumin is also consistent with a dominant mode with strong penetrance. The presence of two separately inherited abnormal T4 transport proteins in the same family suggests that both conditions may be more common than has been thought.

Postpartum thyroiditis and familial dysalbuminemic hyperthyroxinemia.

Familial dysalbuminemic hyperthyroxinemia (FDH) is a syndrome associated with euthyroidism and increased binding of T4 to serum albumin. The combined occurrence of FDH and postpartum hyperthyroidism due to Graves' disease has only been reported in one patient. We now describe the first case of FDH and thyrotoxicosis due to postpartum silent thyroiditis. In a 19-yr-old woman, FDH, suspected on the basis of strikingly elevated analog free T4 (fT4) and total T4 values, but normal two-step fT4 and serum TSH values, was confirmed by [125I]T4 agarose-gel electrophoresis. When FDH and thyrotoxicosis, characterized by markedly elevated analog fT4, total T4, and two-step fT4 values and undetectable TSH values, coexist, the differential diagnosis may be confusing.

Identification of a human serum albumin species associated with familial dysalbuminemic hyperthyroxinemia.

Familial dysalbuminemic hyperthyroxinemia (FDH) is a form of euthyroid hyperthyroxinemia that is due to an increased affinity of serum albumin for T4. Unlike the many physiologically neutral alloalbumins that have been identified by serum electrophoresis, FDH variants have not been reproducibly resolved. In the present study, isoelectric focusing in the presence of the denaturants urea and Nonidet P-40, without reduction, produced two bands in the sera of unrelated FDH subjects in place of each of the major albumin bands in the sera of normal subjects. One band of each FDH pair migrated with the normal band; the second migrated at a slightly lower pI. The identity of the new bands as albumin was confirmed by N-terminal sequencing. The two bands of each pair were present in approximately equal amounts, consistent with the autosomal dominant nature of the condition, the expectation that FDH individuals would be heterozygous for normal albumin (Alb-A), and evidence that high and normal affinity T4-binding sites are equimolar or near equimolar. Similar findings in sera from Hispanic and non-Hispanic FDH subjects suggest that the same structural change may underlie the FDH phenotype from different populations. The slightly lower pI of the FDH-specific bands is consistent with the His for Arg substitution predicted by a G to A base transition recently reported in codon 218 of the gene for the variant albumin (Alb-FDH).

Normal cellular uptake of thyroxine from serum of patients with familial dysalbuminemic hyperthyroxinemia or elevated thyroxine-binding globulin.

To determine whether thyroid hormone-binding proteins in serum, particularly albumin, facilitate the transfer of T4 into human tissues, we studied cellular T4 uptake (CT4) by human liver (Hep G2) cells from medium containing serum from subjects with familial dysalbuminemic hyperthyroxinemia (FDH) and acquired and familial T4-binding globulin (TBG) excess and patients with normal T4-binding to albumin and normal TBG concentrations. Serum from nine subjects with FDH whose mean serum total T4 (TT4) concentration was 203 +/- 27 nmol/L were matched for TT4 concentrations with serum from nine subjects with acquired TBG excess (TT4, 201 +/- 23 nmol/L) and nine subjects with thyrotoxicosis and normal TBG concentrations (TT4, 205 +/- 28 nmol/L). The subjects' CT4 results were compared to their serum free T4 concentration, measured by equilibrium dialysis (DT4), and their serum free T4 index (FT4I) value. The mean serum DT4 value for the subjects with FDH (23 +/- 5 fmol/L) and those with TBG excess (23 +/- 3 fmol/L) were normal, whereas it was elevated (44 +/- 9 fmol/L; P less than 0.001) for the thyrotoxic patients with normal TBG concentrations. The mean CT4 value also was normal for the subjects with FDH (37.7 +/- 4.9 fmol/plate) and those with TBG excess (36.6 +/- 4.6 fmol/plate), but was elevated for the thyrotoxic patients (62.3 +/- 11.2 fmol/plate; P less than 0.001). In all three groups studied, the relationship between individual CT4 and DT4 values was similar to that previously found in subjects with no T4-binding protein abnormalities. The mean serum FT4I value was lower for the subjects with acquired TBG excess (111 +/- 22) than for the subjects with FDH (133 +/- 22; P less than 0.05), and it was much higher for the subjects with thyrotoxicosis (221 +/- 31; P less than 0.001). In the subjects with FDH and those with thyrotoxicosis the normal relationship between CT4 and FT4I was maintained, while in the subjects with acquired TBG excess, FT4I values were lower than expected. In seven of the nine subjects with TBG excess, the abnormality was associated with conditions known to increase its sialic acid content: hepatitis (one subject), pregnancy (four subjects), and estrogen therapy (two subjects). The CT4 values were similar in nine subjects with acquired TBG excess (seven pregnant women and two subjects with chronic active hepatitis) and five subjects with familial TBG excess (34.8 +/- 4.3 vs. 34.0 +/- 8.6 fmol/plate, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Linkage of familial dysalbuminemic hyperthyroxinemia to the albumin gene in a large Amish kindred.

Familial dysalbuminemic hyperthyroxinemia (FDH) is the most common cause of inherited euthyroid hyperthyroxinemia in Caucasians. Transmitted as an autosomal dominant trait, it is always associated with high serum total T4 (TT4) and more rarely with elevated total T3 (TT3) and/or rT3 (TrT3) concentrations. Free T4, by dialysis, and TSH levels are normal, suggesting the presence of a T4-binding protein abnormality. The abnormal serum T4 carrier shares some physical and immunological properties with albumin, suggesting that it may be albumin itself. Here we show linkage between FDH and the albumin gene in a large Amish family of Swiss descent, using as markers a SacI polymorphism in the coding sequence of the albumin gene and the group-specific component (Gc) gene, located less than 1 centimorgan from the albumin gene. Blood samples were obtained from 160 members of this kindred, and 22 had FDH identified by the pattern of T4 binding to serum proteins separated by isoelectric focusing. Serum TT4 values were above the normal range in all subjects expressing the FDH phenotype, and TrT3 levels were above the normal range in only one half. TT4 concentrations correlated positively with TrT3 and TT3. All TT3 values were, however, within the normal range. Free T4 and TSH levels were normal, confirming the euthyroid state in these subjects. FDH was associated with the albumin SacI(+)/Gc 1S haplotype, yielding a LOD (logarithm of the odds ratio) score of 5.53, with a recombination frequency of 0. These data provide strong support that a variant albumin is the cause of FDH in this kindred.

A new family with hyperthyroxinemia caused by transthyretin Val109 misdiagnosed as thyrotoxicosis and resistance to thyroid hormone--a clinical research center study.

Serum transthyretin (TTR) is a protein of liver origin that under normal conditions transports approximately 20% T4. Missense mutations of the TTR gene produce familial amyloidotic polyneuropathy and rarely, euthyroid hyperthyroxinemia (EHT). Of the 3 TTR variants so far identified with increased affinity for T4, Ser6, Thr109, and Met119, only TTR-Thr109 has high enough affinity for T4 to produce consistent hyperthyroxinemia in the heterozygous individuals. Because the mutation GCC-->ACC in codon 109 results in the loss of one Bso FI site in exon 4 of the TTR gene, the use of this enzyme was suggested to screen for TR-Thr109 in subjects with EHT. We investigated a family with dominantly inherited EHT, in which two of eight affected members received ablative thyroid treatment for presumed thyrotoxicosis, and one was misdiagnosed as having resistance to thyroid hormone. All affected individuals had serum reverse T3 concentrations above normal and average T4 50% above the mean of unaffected relatives. Total T3 and TSH levels were within the normal range. Although loss of the Bso FI site in one allele of the two TTR suggested the presence of Thr109, gene sequencing revealed a different mutation in the same codon (GCC-->GTC) producing TTR-Val109. T4-binding to TTR-Val109 was compared to that of the normal TTR-Ala109 and the formerly identified variant TTR-Thr109. Association constants were 1.3, 9.5, and 13.6 X 10(7) M-1 for TTR-Ala109, Val109, and Thr109, respectively. Thus, for equally expressed mutant and normal allele and 20% of serum T4 bound to TTR, the calculated mean serum T4 concentration of heterozygotes for TTR-Val109 should be 50% above the normal mean; the observed value being 55%. These results are in agreement with the observations based on the crystallographic structure of TTR-Thr109 indicating that the extra atoms in Val as in Thr, which are absent in the Ala of the wild type TTR, widen the ligand binding site.

Thyroxine interactions with transthyretin: a comparison of 10 different naturally occurring human transthyretin variants.

Transthyretin (TTR) is a tetrameric protein that transports 15-20% of circulating T4. Alterations in TTR structure can manifest clinically as familial amyloidotic polyneuropathy or euthyroid hyperthyroxinemia. We have measured the relative affinity for T4 of several variant TTR molecules in human plasma. We have compared control plasma to plasma from a patient heterozygous for a [Thr109]TTR mutation associated with a 3-fold increased affinity for T4 and to plasma from patients with familial amyloidotic polyneuropathy with different point mutations in TTR. Relative affinity was measured in an assay in which [125I]T4 bound by TTR was isolated by immunoprecipitation with an antibody specific for TTR. [Thr109]TTR displayed the highest affinity for T4, whereas homozygous [Met30]TTR did not bind appreciable amounts of [125I]T4. The rank order of affinity of the various TTR mutations for T4 was: Thr109 heterozygous > wild type = Ala60 heterozygous = Ile122 heterozygous > His58 heterozygous approximately Tyr77 heterozygous approximately Ser84 heterozygous approximately Ile122 homozygous approximately Met30 heterozygous >> Met30 homozygous TTR. Thus, different point mutations in TTR increase, decrease, or do not affect TTR's affinity for T4. The ability of TTR to form amyloid fibrils does not appear to be related to its affinity for T4. Further study is required to define the molecular basis of alterations in T4 binding induced by point mutations located along the TTR tetramer.

Studies on the nature of iodothyronine binding in familial dysalbuminemic hyperthyroxinemia.

The effects of pH and anionic binding inhibitors were used to test the hypothesis that the increased T4 binding affinity of the variant albumin (Alb-FDH) of familial dysalbuminemic hyperthyroxinemia (FDH) is due to an electrostatic bond with the ionized phenolic hydroxyl of the iodothyronine. As determined by charcoal adsorption from 2% serum in which binding to T4-binding globulin and transthyretin had been inhibited, increased T4 binding by Alb-FDH was pH dependent and proportional to the ionization of the phenolic hydroxyl. Increased T3 binding became apparent above physiological pH, as is consistent with the higher pK of the T3 phenolic hydroxyl. The iodothyroacetic analogs of T4 and T3 developed maximal increases in binding to Alb-FDH at about the same pH as the corresponding iodothyronines. Aspirin, salicylate, warfarin, and chloride, anions that have minimal stereochemical resemblance to the iodothyronines but bind to albumin cationic groups, inhibited T4 binding to FDH sera at concentrations that had little or no effect on binding in normal sera. Increased displacement of T4 from Alb-FDH by salicylate was also evident at therapeutic ratios to a 1:1 dilution of serum in a dialysis system. Aspirin displaced T4 at a lower pH than T3, as is consistent with competition with the ionized iodothyronine phenolic group. These findings suggest that an electrostatic bond between the iodothyronine phenolate and a cationic group on the protein is the basis for the increased affinity and specificity of Alb-FDH for T4.

A novel missense mutation in codon 218 of the albumin gene in a distinct phenotype of familial dysalbuminemic hyperthyroxinemia in a Japanese kindred.

Familial dysalbuminemic hyperthyroxinemia (FDH) is the most common cause of inherited euthyroid hyperthyroxinemia in Caucasians. To our knowledge, no such documentation on Asians exists. Six of 8 members of a 3-generation Japanese family were found by us to carry the FDH phenotype. Serum total T4 levels ranged from 1763.2-2741.3 nmol/L (normal range, 65.6-164.7), serum total T3 levels ranged from 2.73-5.62 nmol/L (normal range, 1.47-2.95), and rT3 levels ranged from 1.08-2.52 nmol/L (normal range, 0.22-0.60). In the proband, the majority of [125I]T4 in serum T4-binding proteins was distributed in albumin fractions, and the isolated albumin had an increased affinity for T4. A guanine to cytosine transition in the second nucleotide of codon 218, resulting in replacement of normal arginine with proline, was detected in 1 of 2 alleles in all 5 subjects of the family with FDH. In all FDH-affected Caucasian subjects from 10 unrelated families with a moderate increase in serum T4, the guanine to adenine transition was demonstrated at the same position of the albumin gene as noted in our patients, but histidine, the replacement amino acid, differed from proline noted in our FDH Japanese subjects. It would thus appear that FDH has ethnic variations.

Coexistence of familial dysalbuminemic hyperthyroxinemia with familial hypercholesterolemia and multiple lipoprotein type hyperlipidemia.

Familial dysalbuminemic hyperthyroxinemia (FDH), an autosomal disorder characterized by an increase in serum albumin binding of thyroxine, has been encountered in a family who was also found to have both familial hypercholesterolemia (FHC) and multiple lipoprotein type hyperlipidemia (MLH). One subject with FHC and two subjects with MLH had FDH. Although some of the laboratory parameters in hyperlipidemic patients with FDH were suggestive of hyperthyroidism, the dialyzable free thyroxine concentrations were in the normal range and the patients were clinically euthyroid. The significance of the occurrence of FDH in hyperlipidemic subjects with hypothyroidism has been discussed, especially in regard to the longer time interval that may be needed to achieve an amelioration of the hypothyroid state during treatment with a normal maintenance dose of thyroxine. Treatment of FDH patients with other drugs may require an altered dosage if the drug binds to the atypical albumin fragments characterizing this disorder.

Familial dysalbuminemic hyperthyroxinemia associated with primary thyroid disease.

This study describes a family with intrinsic thyroid disease in addition to familial dysalbuminemic hyperthyroxinemia, a syndrome associated with euthyroidism and increased binding of thyroxine to serum albumin. The simultaneous occurrence of thyroid disease and elevated serum thyroxine concentrations due to familial dysalbuminemic hyperthyroxinemia may confound the diagnosis of the two concurrent disorders and the subsequent therapy of the thyroid disease.

Familial partial peripheral and pituitary resistance to thyroid hormone: a frequently missed diagnosis?

The diagnosis of partial peripheral and pituitary resistance to thyroid hormone was ultimately made in two boys, 7 and 9 years of age, and a 10-year-old girl who had goiters and hyperthyroxinemia. The boys were treated with propythiouracil and/or thyroidectomy or iodine 131 for suspected thyrotoxicosis but had poorly suppressible serum thyroid-stimulating hormone (TSH) post treatment in spite of the usual L-thyroxine replacement. The girl had increasing goiter size while receiving propylthiouracil, 100 mg every eight hours. These findings led to reevaluation of thyroid hormone dynamics in these children and their families. Twelve additional family members, 3 to 38 years of age, compatible with an autosomal dominant inheritance, were also found to have peripheral and pituitary resistance to thyroid hormone. All affected individuals had elevated serum thyroxine and triiodothyronine levels, normal to slightly elevated triiodothyronine resin uptakes, and a nonsuppressed serum TSH. The five individuals who were given thyrotropin-releasing hormone showed exaggerated TSH responses, which normalized on L-thyroxine therapy. Misdiagnosis in six of 15 family members led to significant morbidity (hypothyroidism, delayed growth, and therapy risk). A nonsuppressed serum TSH in a patient with suspected thyrotoxicosis should lead to suspicion of this disorder. Appropriate management for this condition includes L-thyroxine therapy to decrease goiter size and normalize TSH responses to thyrotropin-releasing hormone.

Diagnostic value of free triiodothyronine in serum.

Serum free T3 concentration has been assessed in various thyroid conditions by a T3 analog method and the results compared with those obtained by equilibrium dialysis in the same individuals. The methodology is easy to perform and reproducible. FT3 determination appears to be especially valuable in detecting borderline thyrotoxicosis as in cases previously cured from thyrotoxicosis but suspected of relapse, or in nontoxic goitrous patients overtreated with T4.

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.

Familial dysalbuminemic hyperthyroxinemia in pregnancy.

A 16-year-old pregnant Puerto Rican woman who had been treated for thyrotoxicosis previously was evaluated for goiter, increased total thyroxine (T4) and triiodothyronine (T3) and free T4 estimate, despite a normal thyroid-stimulating hormone (TSH) concentration. These findings are consistent with a TSH-producing pituitary adenoma or the syndrome of generalized thyroid hormone resistance. However, sera from the patient, her mother and subsequently her newborn daughter demonstrated the increased albumin binding of T4 but not T3 that is characteristic of familial dysalbuminemic hyperthyroxinemia (FDH). The free T4 estimate had been elevated artefactually by the increased affinity of FDH albumin for the analog in a one-step assay. The T3 and T4 concentrations were increased by pregnancy and T4 was increased further by FDH. This first report of FDH recognized during pregnancy emphasizes that the effects of pregnancy on thyroid hormone and TSH concentrations complicate the diagnosis of FDH. It is particularly important to distinguish this benign condition from thyrotoxicosis during pregnancy, because inappropriate treatment may affect fetal development.