Potent thyrotrophin receptor-blocking antibodies: a cause of transient congenital hypothyroidism and delayed thyroid development

TSH-receptor autoantibodies in patients with chronic thyroiditis and hypothyroidism

OBJECTIVES

The reported prevalence of TSH-receptor (TSHR) autoantibodies (TRAb) in patients with chronic thyroiditis (CT) range from 0 to 48%. The objective was to study the prevalence of TRAb in patients with CT and hypothyroidism and to correlate it with gender, age, thyroid dimensions, TSH levels, and autoimmune diseases.

METHODS

The study comprised 245 patients with CT and hypothyroidism (median age 42 years, 193 females, 52 males) and 123 Italian healthy subjects matched for sex and age as controls. TRAb were tested with ELISA using a >2.5 IU/L cut off for positivity. TSHR blocking (TBAb) and TSHR stimulating autoantibodies (TSAb) were measured in 12 TRAb-positive patients using bioassays with Chinese hamster ovary (CHO) cells expressing wild-type or R255D-mutated TSHR.

RESULTS

TRAb positivity was found in 32/245 (13.1%) patients and significantly correlated (p<0.05) with TSH levels. TRAb positivity was significantly higher in males vs. females (p=0.034), in females 16-45 years of age vs. >45 years of age (p<0.05) and in patients with reduced vs. normal/increased thyroid dimensions (p<0.05). Linear regression analysis showed a correlation between TRAb concentrations with age (p<0.05) and TRAb concentrations with TSH (p<0.01). In bioassay with TSHR-R255D all 12 patients tested were TBAb-positive while 33% were also TSAb-positive suggesting the presence of a mixture of TRAbs with different biological activities in some patients.

CONCLUSIONS

TRAb have been found in patients with CT and hypothyroidism. A mixture of TBAb and TSAb was found in some patients and this may contribute to the pathogenesis of thyroid dysfunction during the course of the disease.

Congenital Hypothyroidism due to a Low Level of Maternal Thyrotropin Receptor-Blocking Antibodies

INTRODUCTION

Maternal TSH receptor antibodies (TRAbs) can cross the placenta and affect fetal and neonatal thyroid function. Maternal TSH receptor-blocking antibodies (TBAbs) are a rare cause of congenital hypothyroidism.

CASE REPORT

Following the discovery of a highly elevated TSH on her neonatal screening test, a 10-day-old girl with no familial history of thyroid disorder was referred to the pediatric endocrinology unit. Hypothyroidism was confirmed with a highly elevated TSH (817 mIU/L, reference range 0.4-3.1) and very low levels of FT4 (1.8 pmol/L, reference range 12-22). Anti-TPO antibodies were at 81 IU/mL (reference range <34), TRAbs at 1.7 IU/L (reference range <1.75), and thyroglobulin at 9.4 µg/L (reference range 3.5-77). The thyroid appeared normal on ultrasonography, and no radioiodine uptake was seen on the scintigraphy after the perchlorate discharge test. Concomitantly, a severe maternal hypothyroidism was discovered (TSH 224 mIU/L). The maternal ultrasound appeared normal, anti-TPO antibodies were moderately elevated, and TRAbs were at 3.2 IU/L. TBAbs activity was measured in the mother and her daughter, and a very high and similar blocking activity was observed in both patients (TBAbs 89%, reference range <10%). L-thyroxine treatment was introduced in the newborn and was successfully discontinued at 6.5 months of age, as the TBAbs activity decreased.

CONCLUSION

We report herein a case of transient congenital hypothyroidism with a normal neonatal TRAbs level. In case of maternal TBAbs, similar activity of maternal TBAbs must be expected in the neonate, independently of the neonatal level of TRAbs.

Thyrotropin Receptor Blocking Antibodies

Autoantibodies (Ab) against the thyroid-stimulating hormone receptor (TSHR) are frequently found in autoimmune thyroid disease (AITD). Autoantibodies to the TSHR (anti-TSHR-Ab) may mimic or block the action of TSH or be functionally neutral. Measurement of anti-TSHR-Ab can be done either via competitive-binding immunoassays or with functional cell-based bioassays. Antibody-binding assays do not assess anti-TSHR-Ab functionality, but rather measure the concentration of total anti-TSHR binding activity. In contrast, functional cell-based bioassays indicate whether anti-TSHR-Ab have stimulatory or blocking activity. Historically bioassays for anti-TSHR-Ab were research tools and were used to study the pathophysiology of Graves' disease and Hashimoto's thyroiditis. In the past, bioassays for anti-TSHR-Abs were laborious and time-consuming and varied widely in performance from laboratory to laboratory. Recent advances in the development of cell-based assays, including the application of molecular engineering, have led to significant improvements that have enabled bioassays to be employed routinely in clinical laboratories. The prevalence and functional significance of TSHR blocking autoantibodies (TBAb) in autoimmune hypothyroidism has been less well investigated compared to TSHR stimulating Ab. There is an increasing body of data, however, that demonstrate the clinical utility and relevance of TBAb, and thus the importance of TBAb bioassays, in the diagnosis and management of patients with AITD. In the present review, we summarize the different methods used to measure TBAb, and discuss their prevalence and clinical relevance.

Thyrotropic hormones

Thyroid hormones are crucial for normal cognition and neurodevelopment in children. The introduction of the screening programs for congenital hypothyroidism has decreased the incidence of untreated congenital hypothyroidism. As maternal thyroid disease is common, and may impact on thyroid gland development and function in the fetus, optimal management is crucial. This review discusses thyroid function and the impact of maternal thyroid disease on the fetus and neonate, as well as the influence of thyroid hormones, thyroid antibodies and the excretion of thyroid medication into breast milk on infant thyroid function.

Analytical Performance and Validation of a Bioassay for Thyroid-Blocking Antibodies

BACKGROUND AND OBJECTIVE

A cell-based bioassay for the measurement of thyroid blocking autoantibodies (TBAb) has been recently reported. The analytical performance and validation of this bioassay is assessed and described.

METHODS

Chinese hamster ovary cells expressing a chimeric thyrotropin receptor were treated with bovine (b) TSH and different concentrations of an immunoglobulin G (IgG) monoclonal human TBAb (K1-70). TBAb was measured as a function of luciferase activity relative to bTSH alone and expressed as percent inhibition. Results obtained in the chimeric cell line were compared with those of a wild-type cell line. Analytical performance studies were subsequently performed with the chimeric cell line only.

RESULTS

Immunodepletion of K1-70 IgG by using a protein G-Sepharose column showed that positive percent inhibition in the TBAb bioassay was detectable from K1-70 IgG only. The limit of blank was determined to be 12.2%. The limit of detection was 14% inhibition, equivalent to 0.4 ng/mL K1-70, while the limit of quantitation was 22% (coefficient of variation [CV] 12%) equivalent to 0.625 ng/mL K1-70. The dynamic range was between 14 ± 3.7 (mean % inhibition ± standard deviation) and 101 ± 2.6, equivalent to 0.4-10 ng/mL K1-70. The linear range was between 22 ± 2.6 and 93 ± 0.6 inhibition, equivalent to 0.625-5 ng/mL K1-70. The upper limit of the 99th percent reference range was 34% inhibition. In two laboratories, CV values for the intra- and inter-assay precisions for K1-70 ranged from 2% to 12% and from 1.7% to 14.5%, respectively. For patient sera, the CV values for the intra- and inter-assay precisions ranged from 3% to 9% and from 3% to 11%, respectively. No interference was found when follicle-stimulating hormone, luteinizing hormone, and human chorionic gonadotrophin were tested in the TBAb bioassay. The median of % inhibition values in 40 TBAb positive sera from patients with autoimmune thyroid disease were 93.5 (range 25-103) and 92 (range 64-107) for the wild type and chimeric cell lines, respectively. Further, all 40 samples of patients with various non-thyroidal autoimmune diseases were TBAb negative.

CONCLUSIONS

This TBAb bioassay exhibits excellent analytical performance and high level of reproducibility.

Colostrum from cows immunized with a vaccine associated with bovine neonatal pancytopenia contains allo-antibodies that cross-react with human MHC-I molecules

In 2006, a new haemorrhagic syndrome affecting newborn calves, Bovine Neonatal Pancytopenia (BNP), was reported in southern Germany. It is characterized by severe bleeding, destruction of the red bone marrow, and a high case fatality rate. The syndrome is caused by alloreactive, maternal antibodies that are ingested by the calf with colostrum and result from a dam vaccination with one particular vaccine against Bovine-Viral-Diarrhoea-Virus. Because bovine colostrum is increasingly gaining interest as a dietary supplement for human consumption, the current study was initiated to elucidate whether BNP alloantibodies from BNP dams (i.e. animals that gave birth to a BNP-affected calf) cross-react with human cells, which could pose a health hazard for human consumers of colostral products. The present study clearly demonstrates that BNP alloantibodies cross-react with human lymphocytes in vitro. In agreement with previous reports on BNP, the cross-reactive antibodies are specific for MHC-I molecules, and sensitize opsonised human cells for in vitro complement lysis. Cross-reactive antibodies are present in serum and colostrum of individual BNP dams. They can be traced in commercial colostrum powder manufactured from cows immunized with the vaccine associated with BNP, but are absent from commercial powder manufactured from colostrum excluding such vaccinated cows. In humans alloreactive, MHC-I specific antibodies are generally not believed to cause severe symptoms. However, to minimize any theoretical risk for human consumers, manufacturers of bovine colostrum for human consumption should consider using only colostrum from animals that have not been exposed to the vaccine associated with BNP.

Thyroid autoantibodies in pregnancy: their role, regulation and clinical relevance

Autoantibodies to thyroglobulin and thyroid peroxidase are common in the euthyroid population and are considered secondary responses and indicative of thyroid inflammation. By contrast, autoantibodies to the TSH receptor are unique to patients with Graves' disease and to some patients with Hashimoto's thyroiditis. Both types of thyroid antibodies are useful clinical markers of autoimmune thyroid disease and are profoundly influenced by the immune suppression of pregnancy and the resulting loss of such suppression in the postpartum period. Here, we review these three types of thyroid antibodies and their antigens and how they relate to pregnancy itself, obstetric and neonatal outcomes, and the postpartum.

Transient congenital hypothyroidism due to thyroid-stimulating hormone receptor blocking antibodies: a case series

We describe seven infants with transient congenital hypothyroidism (CH) due to maternal thyroid-stimulating hormone receptor (TSH-R) blocking antibodies (TRAb) identified over three decades of newborn screening for CH in Wales, UK that represents a minimum incidence of 1.6% of CH cases. Infants with transient CH due to maternal TRAb presented with a spectrum of clinical and biochemical hypothyroidism. Blood spot TSH concentrations ranged 60.5-332 mIU/L. CH was confirmed by plasma thyroid function tests in all cases (plasma TSH ranged 21-752 mIU/L). The seven infants belonged to five different families. On examination, four infants were clinically hypothyroid. Five infants had a thyroid ultrasound, of which three were abnormal. All infants were treated with thyroxine, which was subsequently withdrawn from three. Following thyroxine withdrawal, one infant resumed normal thyroid function and two developed compensated hypothyroidism. Of the five mothers, two had undiagnosed hypothyroidism and three were receiving thyroxine for longstanding hypothyroidism. Thyroid peroxidase antibody (aTPO) was measured in four and was negative in two, borderline positive in one and strongly positive in another. TRAb was measured in all five women and was strongly positive in all of them. This case series highlights the importance of identifying CH due to TRAb by investigating both the infant and the mother following a raised TSH found on newborn screening. The identification of those infants with transient CH caused by maternal transfer of TRAb is essential for optimizing management during childhood (including potential withdrawal of thyroxine replacement in the longer term) and in any subsequent pregnancy.

Update: newborn screening for endocrinopathies

Congenital hypothyroidism and congenital adrenal hyperplasia are included in many newborn screening (NBS) panels worldwide and in all state-sponsored programs in the United States. Both conditions meet the fundamental prerequisites for NBS: high incidence in the population; biomarkers in the dried blood specimen that are easily detected; and, effective therapies to lessen, if not prevent, the sequelae of late or no treatment. In this review, the history of NBS is discussed for these 2 conditions. The technologies and protocols used in their detection, and related subjects such as genetics, and treatment and outcomes, are also discussed.

Benign thyroid disease: what is the role of nuclear medicine?

Nuclear medicine is directly involved in both the diagnosis and treatment of benign thyroid disease, which requires an understanding of the pathophysiology and management of thyroid disorders in addition to expertise in nuclear methodology. Thyroid uptake and imaging, the principal nuclear tests in thyroid disease, may be used as follows: (1) Differential diagnosis of hyperthyroidism: A very low thyroid uptake suggests destructive ("subacute") thyroiditis, a self-limited disorder, whereas a normal or elevated uptake is consistent with toxic nodular goiter and Graves' disease. Scintigraphic characteristics also help differentiate between nodular and Graves' disease. (2) Function of thyroid nodules: Fine-needle aspiration biopsy with cytological examination (FNAB) is used routinely to assess for malignancy in thyroid nodules. Scintigraphy may be of assistance before FNAB. "Hot" nodules are generally benign and do not require FNAB, while "cold" nodules may be malignant. (3) Differential diagnosis of congenital hypothyroidism: Scintigraphy combined with ultrasound examination may be used to identify such conditions as thyroid agenesis, dyshormonogenesis, and incomplete thyroid descent. Treatment of Graves' disease and toxic nodular disease with (131)I may require greater clinical involvement and decision analysis compared with thyroid uptake and imaging. The following aspects of treatment are particularly important: (1) Risk: Radioiodine treatment may occasionally aggravate hyperthyroidism, Graves' ophthalmopathy, and airway obstruction caused by large, nodular goiters. Alternative treatments, including the temporary use of antithyroid drugs, and surgery for nodular goiters, may be considered. (2) Radioiodine dose: Cure of hyperthyroidism with a single (131)I treatment is desirable, though not always possible. Such factors as a large goiter, severe hyperthyroidism, and prior propylthiouracil therapy, may contribute to treatment failure. (3) Informed consent: A detailed discussion with the patient regarding the clinical risks, outcomes, and side effects of (131)I is a critical component of successful management.

Graves' disease and coexisting struma ovarii: struma expression of thyrotropin receptors and the presence of thyrotropin receptor stimulating antibodies

Struma ovarii is a rare cause of hyperthyroidism and particularly rare in patients with coexisting Graves' disease. We describe a 28-year-old female who presented with symptoms and signs of hyperthyroidism (free thyroxine [FT(4)] 39 pmol/L, thyrotropin [TSH] < 0.05 mU/L) and associated ophthalmopathy, consistent with Graves' disease. The patient relapsed twice: once after initial successful management with carbimazole and subsequently after subtotal thyroidectomy. Radioisotope scanning showed focal uptake bilaterally in the neck and believing this was the source of thyroid hormone excess, carbimazole was restarted. A left ovarian mass was found on ultrasound during the investigation of unrelated nephrotic syndrome resulting from focal segmental glomerulosclerosis. A 555-g struma ovarii was removed surgically. Hypothyroidism developed postoperatively (FT(4) 9.7 pmol/L, TSH 36 mU/L). Circulating TSH receptor stimulating antibodies were positive and immunohistochemical studies confirm the presence of TSH receptors on the struma ovarii. The demonstration of TSH receptors on the struma ovarii increases previous speculation that struma ovarii growth and function may be augmented by the circulating TSH receptor stimulating antibodies of Graves' disease.

Genetics of congenital hypothyroidism

Congenital hypothyroidism is the most common neonatal metabolic disorder and results in severe neurodevelopmental impairment and infertility if untreated. Congenital hypothyroidism is usually sporadic but up to 2% of thyroid dysgenesis is familial, and congenital hypothyroidism caused by organification defects is often recessively inherited. The candidate genes associated with this genetically heterogeneous disorder form two main groups: those causing thyroid gland dysgenesis and those causing dyshormonogenesis. Genes associated with thyroid gland dysgenesis include the TSH receptor in non-syndromic congenital hypothyroidism, and Gsalpha and the thyroid transcription factors (TTF-1, TTF-2, and Pax-8), associated with different complex syndromes that include congenital hypothyroidism. Among those causing dyshormonogenesis, the thyroid peroxidase and thyroglobulin genes were initially described, and more recently PDS (Pendred syndrome), NIS (sodium iodide symporter), and THOX2 (thyroid oxidase 2) gene defects. There is also early evidence for a third group of congenital hypothyroid conditions associated with iodothyronine transporter defects associated with severe neurological sequelae. This review focuses on the genetic aspects of primary congenital hypothyroidism.