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.

Congenital central isolated hypothyroidism caused by a homozygous mutation in the TSH-beta subunit gene

We report a Belgian girl born in 1983 with isolated thyrotropin (TSH) deficiency. Hypothyroidism without goiter was diagnosed at the age of 2 months, with extremely low total thyroxine (T4) at 0.3 microg/dL (4 nmol/L; N[normal]: 5.6-11.4 microg/dL). Basal TSH, only moderately elevated at 14.8 mU/L (N: 0-5.3; competitive radioimmunoassay, RIA), increased to 18.2 mU/L after thyrotropin-releasing hormone (TRH) stimulation, whereas prolactin increased normally. At age 15 years, after withdrawal of levothyroxine (LT4) therapy for 6 weeks, TRH stimulation slightly increased serum TSH using two immunometric assays, from less than 0.03 to 0.07 and from 0.2 to 0.3 (a monoclonal and polyclonal antibody), and from 1.9 to 4.1 mU/L using a polyclonal TSH antibody and iodinated recombinant TSH. Sequencing of the TSH-beta subunit gene revealed a homozygous single nucleotide deletion in codon 105 producing a frame shift that results in a truncated TSH-beta with nonhomologous 9 carboxyterminal amino acids and a loss of the 5 terminal residues. This mutation was previously reported in one Brazilian and two German families. The abnormal, and presumably biologically inactive, TSH can be detected in serum using appropriate antibodies. Its relatively small amount in serum is due to either reduced secretion or rapid degradation. The occurrence of the same mutation in three families of different ethnic origin suggests that this mutation may be prevalent in the population. Common ancestry or de novo mutations in a hot spot cannot be excluded. Finally, we must be aware that neonatal screening of congenital hypothyroidism based on blood spot TSH measurement will not detect this rare but severe genetic defect.

Familial dysalbuminemic hypertriiodothyroninemia: a new, dominantly inherited albumin defect

We report the abnormal albumin in members of a Thai family that presented with high serum total T3 but not T4 when measured by radioimmunoassay. In contrast, total T3 values were very low when measured by ELISA and chemiluminescence. The subjects have no goiter, and clinically euthyroid. Their serum free T4, free T3, and TSH were normal. Spiking of T3 to affected serum showed good recovery by radioimmunoassay, but very poor recovery by ELISA and by chemiluminescence. The immunoprecipitation with labeled T3 bound to albumin showed high percent precipitation in affected serum. T3-binding studies showed that the association constant of serum albumin in affected subjects was 1.5 x 10(6) M-1 or 40-fold that of unaffected relatives of 3.9 x 10(4) M-1. In contrast, the Ka of HSA for T4 in an affected subject was only 1.5-fold that of a normal. Albumin complementary DNA from leukocytes of affected member was amplified and sequenced. We found the second nucleotide of normal codon 66 (CTT), a thymine, was substituted by a cytosine (CCT), resulting in the replacement of the normal leucine by proline. This is the first report of variant albumin causing familial dysalbuminemic hypertriiodothyroninemia.

Thyroid function tests and characterization of thyroxine-binding globulin in the carbohydrate-deficient glycoprotein syndrome type I

Carbohydrate-deficient glycoprotein (CDG) syndrome is a newly recognized hereditary disorder that presents with psychomotor retardation, cerebellar ataxia, peripheral sensorimotor neuropathy, and, variably, skeletal abnormalities, lipodystrophy, and retinitis pigmentosa. These abnormalities appear to be produced by a defect that causes reduced carbohydrate content in glycoproteins. We studied seven patients with CDG type I belonging to five unrelated families. The concentration of serum TBG, a glycoprotein of hepatic origin, was measured by RIA and T4 saturation and was found to be below the normal range in three of the seven patients and normal in four of them. More than half of the total serum TBG had reduced sialic acid content and localized on isoelectric focusing (IEF) as two prominent bands cathodal to the three major bands of normal TBG. The latter two bands are responsible for the characteristic IEF pattern or CDG syndrome. TBG in patients with CDG had immunoreactivity indistinguishable from that of normal TBG and had normal affinity for T4, T3, and rT3. Serum total T4, T3, and rT3 were below the normal range in seven, five, and seven patients, respectively. The free T4 index was also below normal in four patients, but the free T4 concentration, measured by equilibrium dialysis at low dilution, and serum TSH were in the midnormal range. The serum total T4 and rT3 levels were disproportionately reduced relative to the serum TBG concentration and compared to the concentrations of these iodothyronines in matched subjects with inherited partial TBG deficiency. Chronic illness cannot explain these changes, because, contrary to patients with nonthyroidal illness, those with CDG had significantly higher serum total T3/T4 and lower rT3/T4 ratios. It is concluded that IEF of TBG is a rapid and simple method for the diagnosis of CDG type I and that the abnormal pattern can be detected as early as 5 days postpartum. Patients with CDG are chemically euthyroid, and it is postulated that the reduction in serum iodothyronine concentrations beyond that explained on the basis of low TBG levels may be due to the interference with binding to TBG by an unidentified substance.

Neonatal detection of generalized resistance to thyroid hormone

Generalized resistance to thyroid hormone (GRTH) is an inherited disease that is usually suspected when elevated serum thyroid hormone levels are associated with nonsuppressed thyrotropin. Often these test results are obtained because of short stature, decreased intelligence, and/or hyperactivity with learning disability noted in childhood and adolescence, or because of goiter in adulthood. We detected GRTH at birth by analysis of blood obtained during routine neonatal screening. The proposita, born to a mother with GRTH, had a thyrotropin level of 26 mU/L and a corresponding thyroxine concentration of 656 nmol/L (normal, 84 to 232 nmol/L). Administration of thyroid hormone in doses eightfold to 10-fold above replacement levels (liothyronine sodium, 21 micrograms/kg per day, and levothyroxine sodium, 44 micrograms/kg per day) were required to reduce serum thyrotropin to normal levels without induction of hypermetabolism. This case, and the retrospective finding of high thyroxine levels in five newborns subsequently diagnosed as having GRTH, suggest that measurement of thyroxine at birth, in conjunction with thyrotropin, could allow the early detection of GRTH.

Anterior pituitary: triiodothyronine and/or dexamethasone induced changes in protein formation in thyroidectomized and/or adrenalectomized rats

Protein formation in the anterior pituitary was investigated in vitro in thyroidectomized (TX) and/or adrenalectomited (AX) rats treated with a single dose of 100 micrograms/100 g of 3,5,3'-triiodothyronine (T3) and/or with a single dose of 10 micrograms/100 g of dexamethazone (DEX) 12 h before sacrifice. Male Wistar rats of a specific pathogen free colony 6 weeks after TX and/or AX receiving 1% calcium chloride and/or saline after surgery were used in the experiments. Non-pooled anterior pituitaries (in acellular condition) complemented with all essential amino acids, CPK, creatine phosphate in a HEPES buffer containing potassium acetate, magnesium acetate and dithiothreitol, were incubated with 35S-methionine at 28 degrees C for 10 or 40 min. The reaction was stopped by EDTA followed by RNAase plus DNAase treatment and the samples were analyzed for total 35S-methionine incorporation or by SDS 12.5% polyacrylamide gel slab electrophoresis (PAGE). As compared to intact rats (100%), TX and/or AX caused a significant diminution of the total 35S-methionine incorporation into protein ranging from 33% to 68% that may be easily restored to 107% by T3 plus DEX treatment. PAGE analysis reflects an appreciable relation between T3 administration and 21.5 kDa protein (growth hormone) formation in the anterior pituitary. In addition, the effect 5,5'-diphenylhydantoine (DPH) on 35S-methionine incorporation in relation to T3 nuclear specific binding was investigated. The data suggest that the decreased protein synthesis de novo is due to a significant diminution of T3 specific binding to nuclear receptors in the anterior pituitary.

Direct application of radioiodinated aminoacyl tRNA for radiolabeling nascent proteins

A two-step procedure to incorporate 125I-iodotyrosine into protein synthesized in a reticulocyte lysate is described. In the first step, the iodination of tyrosyl tRNA was catalyzed by a solid-state glycouril compound. More than one-third of 200 microCi of radioiodine became bound to 70 micrograms of aminoacyl tRNA after 15 min at 0 degrees C. The isotope was distributed in a three-to-one ratio of monoiodotyrosine to di-iodotyrosine. In the second step, the soluble product of the radioiodination was transferred directly into a nuclease-treated reticulocyte lysate coded with RNA isolated from the human hepatoma cell line Hep G2. Fractional recovery of radioiodine in nascent protein was maximally 7.6%. Reaction of the product of translation with antibody against alpha-antitrypsin separated an 125I-containing protein having a molecular weight estimated as 47,000. The synthesis of unprocessed alpha-antitrypsin was confirmed by cleavage of the labeled protein with leader peptidase and by its displacement from immunocomplex formation with purified alpha-antitrypsin. The amount of 125I incorporated into alpha-antitrypsin was proportionate to iodinated tRNA additions up to a concentration of 70 micrograms/ml. The synthesis of alpha-antitrypsin as detected in radioautograms after gel electrophoresis was more than twice as sensitive using radioiodinated aminoacyl tRNA as compared with [35S]methionine. Iodine labeling of thyroxine-binding globulin was also demonstrated in the translation product of Hep G2 RNA. Since the specific activity of the radioiodine is high and the means for detection of the isotope efficient, the method described can facilitate the demonstration of quantitatively minor translation products.

Elevated serum thyroglobulin level in congenital thyroxine-binding globulin deficiency

Serum thyroglobulin (TG) is normally under TSH control. Serum TG levels are elevated during increased thyroid gland stimulation and suppressed by exogenous thyroid hormone. High serum TG levels are also found with thyroid gland damage and in patients with differentiated thyroid neoplasms. Congenital T4-binding globulin deficiency was found in this study to be an additional condition in which serum TG levels may be elevated. Elevated TG levels were found in 13 of 36 patients (36%) with congenital TBG deficiency compared to 1 of 27 unaffected relatives (4%). Mean TSH and free T4 index values were not significantly different. A postulated mechanism involves transient TSH stimulation of the thyroid after transient small declines in circulating free hormone levels due to the decreased extrathyroidal pool of thyroid hormone associated with T4-binding globulin deficiency.

The influence of percutaneous fine needle aspiration on serum thyroglobulin

To determine whether percutaneous needle aspiration of the thyroid affects tests of thyroid function, in particular thyroglobulin (TG), serum TG, T4, free T4 index, T3, and TSH were measured before and after percutaneous needle aspiration biopsy of the thyroid in 25 subjects. Seven control subjects were tested before and after vigorous external manual palpation of the thyroid. Serial measurements were made additionally in 3 subjects undergoing thyroid surgery to assess how quickly serum TG increases after injury. The results were analyzed, and statistically significant differences between paired results were defined if the differences were greater than the maximum interassay variation in 11 consecutive assays. Eleven out of 25 patients had statistically significant elevations of serum TG after aspiration. None of the seven who underwent external manual palpation of the thyroid gland had elevation of serum TG. With three exceptions, there were no significant changes in serum T4, free T4 index, T3, and TSH in either group. Marked elevations in serum TG occurred within 2 min after open manual palpation, diathermy, and excision. The results were analyzed and correlated with factors that might lead to release of TG from the thyroid during needle aspiration. No positive correlation was observed with the apparent degree of trauma, the size of nodule, the TG content, volume or character of aspirate, or the time elapsed from aspiration to withdrawal of the blood sample. Correlation of serum TG elevation with final diagnosis did not show a significant trend; however, the existence of a possible relationship needs further studies. We conclude that serum for TG measurement should be obtained before percutaneous thyroid aspiration biopsy.

T4 transfer RNAs: codon recognition and translational properties

T4 phage transfer RNAs recognize the previously assigned codons for a given amino acid; however, they tend to prefer code words that are less well recognized by their host. The phage transfer RNAs are more effective in polypeptide synthesis with T4 rather than Escherichia coli messenger RNAs.

Detection of bacteriophage T4- and T5-coded transfer RNAs

A hybridization procedure using mixtures of radioactive aminoacyl-tRNA is described for detecting new phage-induced tRNA species. Five phage-coded tRNA species have been identified from T4 phage infected bacteria and 14 from T5 phage infected cells.