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PubMed1994

A point mutation in the human serum albumin gene results in familial dysalbuminaemic hyperthyroxinaemia.

Using DNA samples obtained from two unrelated patients, diagnosed as having familial dysalbuminaemic hyperthyroxinaemia (FDH), exons 1-14 which span the entire coding region of the human serum albumin (HSA) gene were amplified by the polymerase chain reaction. The sequence of each of the 14 DNA fragments was then determined. In each case a point mutation was identified at nucleotide 653 which causes an Arg to His substitution at amino acid position 218. The substitution was confirmed by amino acid sequencing of a mutant peptide resulting from tryptic digestion of the protein. Abnormal affinity of FDH HSA for a thyroxine (T4) analogue was verified by an adaptation of the procedure used in routine free T4 measurement. The location of the mutation is discussed in relation to other studies on the binding properties of HSA.

Amino Acid Sequence↗
PubMed1987

Familial dysalbuminaemic hyperthyroxinaemia.

Familial dysalbuminaemic hyperthyroxinaemia (FDH) can be confused with thyrotoxicosis if clinical signs and laboratory tests are misinterpreted. We describe three members of the same family with FDH who were erroneously treated for thyrotoxicosis. Screening of other family members resulted in the discovery of a further six patients at risk of being misdiagnosed as thyrotoxic. Clinical and biochemical findings relevant to the diagnosis of FDH are discussed.

Adult↗
PubMed1990

Thyroid function tests in amyloid goitre.

We present two patients with amyloid goitre due to primary systemic amyloidosis which was confirmed at post-mortem. Both were clinically euthyroid but had hyperthyroxinaemia and other thyroid function tests suggestive of thyrotoxicosis.

Adult↗
PubMed1990

A longitudinal study of changes in erythrocyte zinc concentration in hyperemesis gravidarum.

Erythrocyte zinc concentration and plasma thyroid hormones were measured in 32 patients admitted to hospital because of hyperemesis gravidarum. At presentation, 8 patients had elevated total and free thyroxine concentrations. The initial erythrocyte zinc concentration in these 8 patients was not different from the others, but in 5 of them, a transient drop in the erythrocyte zinc concentration was observed 2-12 weeks later, and which returned to normal towards the end of pregnancy. The lowest erythrocyte zinc concentration in the hyperthyroxinaemic group (171.0 +/- 31.7 mumol/l of RBC) was significantly lower than that of the normothyroxinaemic group (214.2 +/- 33.9 mumol/l of RBC) (p less than 0.01). This indicates that hyperthyroxinaemia in patients with hyperemesis gravidarum represents true hyperthyroidism, but is different from classical thyrotoxicosis in that the elevation of thyroid hormones is transient.

Carbonic Anhydrases↗
PubMed1986

Thyroid function tests in patients with familial dysalbuminaemic hyperthyroxinaemia (FDH).

Two patients with familial dysalbuminaemic hyperthyroxinaemia (FDH) are described in whom the albumin variant resulted in raised total T4 levels, and artefactually raised free T4 using a 'single-step' technique employing an analogue of T4 as tracer. The first patient was clinically euthyroid and presented with relapse of schizophrenia and abnormal thyroid function tests (total T4 336 nmol/L, total T3 4.2 nmol/L, TSH 1.8 mU/L, free T4 73 pmol/L). These results led to diagnostic confusion and the patient was treated with a short course of anti-thyroid drugs. The second patient had signs and symptoms of thyrotoxicosis at her first visit but was clinically euthyroid 5 months later when she was 10 weeks pregnant. Thyroid function tests were total T4 259 nmol/L, total T3 3.6 nmol/L, TSH 3.8 mU/L, free T4 46 pmol/L. Further studies showed both patients to be biochemically euthyroid. A variant albumin was confirmed in both patients by a screening test for FDH and by reverse-flow electrophoresis. Family studies on 10 relatives of the first patient identified eight with FDH. A simple screening procedure for the indentification of FDH is described and the use of laboratory tests in suspected cases is discussed.

Adult↗
PubMed1990

Non-isotopic, two-step free thyroxine immunoassay: a better measure of free thyroxine than analogue radioimmunoassay.

Plasma or serum free thyroxine (T4) was measured by a novel non-isotopic, two-step immunoassay in 373 consecutive patients attending a thyroid clinic, in whom thyroid status was categorized according to clinical findings, supported by routine thyroid function tests. The 95% confidence limit of free T4 in the euthyroid patients (n = 112) was 7-20 pmol/L. Free T4 concentrations within the reference range were found in six of 40 patients with primary hypothyroidism and nine of 182 patients with overt thyrotoxicosis, six of whom had T3 toxicosis. Serum or plasma free T4 measured by the two-step method showed improved diagnostic specificity over an analogue RIA in selected groups of euthyroid patients in whom abnormal binding of analogue T4 can affect the validity of the result. Free T4 results found by analogue RIA and the two-step method in 58 patients who were receiving thyroxine replacement therapy were similar. The between-assay precision of the two-step method was poor ranging from a coefficient of variation of 9.7% to 19.3% over a free T4 concentration range of 5.0 to 46.0 pmol/L. We conclude that the two-step methodology offers diagnostic advantages for a laboratory which receives specimens from such patients for exclusion of thyroid disease but that improved assay precision is required before it could be used in a routine situation.

Autoantibodies↗
PubMed1987

Familial dysalbuminaemic hyperthyroxinaemia and other causes of euthyroid hyperthyroxinaemia.

Clinical and biochemical studies on a family in which 3 members have familial dysalbuminaemic hyperthyroxinaemia (FDH) are presented. They were clinically euthyroid with elevated serum thyroxine (T4) and free T4 indices but normal free T4 by equilibrium dialysis and normal serum triiodothyronine (total and free). All thyroid function tests on the remaining family members were normal. The inheritance is consistent with autosomal dominance. Also presented are data on 4 unrelated patients with FDH and two patients with T4 autoantibodies. The methods for detecting FDH, T4 antibodies and other causes of euthyroid hyperthyroxinaemia are now freely available. Since these anomalies may be more common than previously supposed, clinical awareness of the conditions is necessary to protect patients from the consequences of incorrect diagnosis of thyrotoxicosis.

Adult↗
PubMed2003

Clinical characteristics of patients with thyrotropin-secreting pituitary adenoma.

BACKGROUND AND PURPOSE: Thyroid-stimulating hormone (thyrotropin, TSH)-secreting pituitary adenoma is a very rare cause of hyperthyroidism. Diagnosis of this condition is often delayed due to lack of availability of TSH radioimmunoassay (RIA), the failure to recognize the utility of RIA and the incorrect attribution of the condition to other causes of thyrotoxicosis. This retrospective study analyzed the clinical characteristics of patients with this disorder treated from 1991 to 2002. METHODS: Seven patients (6 females, 1 male; mean age, 48 years; range, 33 to 72 years) with a diagnosis of TSHsecreting pituitary adenoma based on detectable TSH levels with high serum free thyroid hormone or triiodothyronine concentrations and pituitary lesions found on neuroimaging were included in this study. Patient records including clinical features, endocrine studies, immunohistochemistry studies, and response to treatment were reviewed. RESULTS: All 7 patients had hyperthyroidism, elevated free thyroxine or triiodothyronine levels, and unsuppressed levels of TSH. Imaging studies demonstrated a pituitary mass or lesion in all patients. Six patients had macroadenomas and 1 patient had a microadenoma. One of the patients had coexisting acromegalic features and hypersecretion of growth hormone was diagnosed. All of the patients had been treated with thionamides or thyroidectomy for presumed primary hyperthyroidism. Serum alpha-subunit level was uncharacteristically normal in 2 patients and elevated in 1 patient. Alpha-subunit/TSH molar ratios were elevated in 3 patients. Five patients underwent transsphenoidal adenomectomy but only one of them remained well-controlled at follow-up. Three patients received administration of somatostatin analogs and they achieved normalization of serum TSH and free thyroid hormones during the period of therapy. CONCLUSIONS: TSH immunoassay has an important role in the evaluation of hyperthyroid patients to determine the presence of inappropriate secretion. TSH-secreting pituitary adenoma exhibits heterogeneity in clinical presentation, hormonal expression and therapeutic response.

Acromegaly↗
PubMed2003

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.

Adult↗