Alterations of neonatal thyroid function

Grüters A, Krude H, Biebermann H, Liesenkötter KP, Schöneberg T, Gudermann T. Alterations of neonatal thyroid function. Acta Pædiatr 1999; Suppl 428: 17–22. Stockholm. ISSN 0803–5326
Recent progress has been made in understanding the pathogenesis of neonatal thyroid disorders. Autosomal recessive inheritance of mutations of the thyroid peroxidase and thyroglobulin genes has been described in some patients with congenital hypothyroidism (CH) and a family history of CH. Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis. These discoveries are important for patients with CH diagnosed by neonatal screening, as these patients will have normal fertility. The molecular genetic analysis of mutations of the TSH gene in patients with familial and sporadic cases of isolated central CH, who are missed by TSH screening programmes, now enables rapid diagnosis and appropriate therapy in the neonate. In newborn infants with severe non-autoimmune hyperthyroidism, autosomal dominant gain-of-function mutations in the TSH receptor gene have been demonstrated. In these patients, molecular genetic studies are extremely helpful in therapeutic decision making, as early thyroid ablation is the only effective treatment that avoids the sequelae of long-term hyperthyroidism. Molecular genetic studies are therefore useful in the diagnostic work-up of neonatal thyroid alterations. □ Congenital hypothyroidism, molecular pathogenesis, neonatal hyperthyroidism     

Alterations of neonatal thyroid function

Recent progress has been made in understanding the pathogenesis of neonatal thyroid disorders. Autosomal recessive inheritance of mutations of the thyroid peroxidase and thyroglobulin genes has been described in some patients with congenital hypothyroidism (CH) and a family history of CH. Autosomal recessive inheritance of mutations of the thyrotrophin (TSH) receptor gene has also been reported in patients with CH and thyroid hypoplasia, and autosomal dominant mutations of the PAX8 gene have been described in patients with different forms of thyroid dysgenesis. These discoveries are important for patients with CH diagnosed by neonatal screening, as these patients will have normal fertility. The molecular genetic analysis of mutations of the TSH gene in patients with familial and sporadic cases of isolated central CH, who are missed by TSH screening programmes, now enables rapid diagnosis and appropriate therapy in the neonate. In newborn infants with severe non-autoimmune hyperthyroidism, autosomal dominant gain-of-function mutations in the TSH receptor gene have been demonstrated. In these patients, molecular genetic studies are extremely helpful in therapeutic decision making, as early thyroid ablation is the only effective treatment that avoids the sequelae of long-term hyperthyroidism. Molecular genetic studies are therefore useful in the diagnostic work-up of neonatal thyroid alterations.     

High frequency of D727E polymorphisms in exon 10 of the TSHR gene in Brazilian patients with congenital hypothyroidism

Congenital Hypothyroidism affects between 1:3000 and 1:4000 newborn infants in iodine-sufficient regions. Some studies have shown that mutations and polymorphisms in the TSH receptor gene are responsible for this disease. In the present study, mutations of exon 10 of the TSH receptor gene were investigated in Congenital Hypothyroidism patients. In the present study a sample of 90 Brazilian patients with primary congenital hypothyroidism was analyzed. Genomic DNA was isolated from peripheric blood samples. Exon 10 of the TSH receptor gene was amplified by PCR, and amplicons were automatically sequenced. Three nucleotide alterations were identified: c.1377G>A (A459A), c.1935G>A (L645L), and c.2181C>G (D727E). A459A polymorphism was also described previously in patients with thyroid cancer. The nucleotide alteration L645L was found in a single patient. This is the first time the L645L mutation has been described. D727E polymorphism showed high frequency (allele frequency 10%) in present study when compared to others reports.     

An activating mutation of the thyrotropin receptor gene in hereditary non-autoimmune hyperthyroidism

The thyroid stimulating hormone (TSH) receptor gene displays a diverse spectrum of activating and inactivating mutations. We report a germline activating mutation M463V of the TSH receptor gene in two siblings with hereditary non-autoimmune hyperthyroidism. The onset of disease in the affected members of the pedigree occurred during childhood or adolescence. The significance of diagnosing activating TSHR mutations lies in therapeutic management and genetic counseling; thyroid ablation is advocated as first line treatment.     

A mutation in thyroid hormone receptor beta causing "resistance to thyroid hormone" in a neonate

Resistance to thyroid hormone (RTH) is an inherited syndrome characterized by reduced tissue responsiveness to thyroid hormones. The main defects are due to mutations in thyroid hormone receptor beta (TRbeta). A male, term neonate was admitted because of indirect hyperbilirubinemia and polycythemia. Physical examination revealed ophtalmopathy. High serum T? with unsupressed thyroid stimulating hormone (TSH) levels suggested RTH. In this presented case, A317T mutation was detected on exon 9 of the TRb-1 gene and precise diagnosis had been confirmed with genetic testing. In neonates and infants exhibiting hypo or hyperthyroidism features with increased circulating levels of thyroid hormones with a normal or increased serum TSH concentration should raise the suspicion of RTH.     

Genetic defects in thyroid hormone synthesis.

Thyroid hormone synthesis requires a normally developed thyroid gland, a properly functioning hypothalamic-pituitary-thyroid axis, and sufficient iodine intake. This article focuses on genetic defects in this axis. Defects that are primarily of developmental origin are discussed in our associated article in this issue. Defects in hormone synthesis usually are associated with the development of a goiter, provided that the bioactivity and action of thyrotropin (TSH) are not impaired. In contrast, hypoplasia of the gland may be caused by developmental defects, bioinactive TSH, or resistance to TSH at the level of the receptor or its signaling pathway. At the other end of the spectrum, hyperthyroidism may result from gain of function mutations in genes regulating growth and function.     

A family with a novel TSH receptor activating germline mutation (p.Ala485Val)

Autosomal dominant nonautoimmune hyperthyroidism (ADNAH) is caused by gain of function mutations in the TSH receptor (TSHr) gene and characterized by toxic thyroid hyperplasia with a variable age of onset in the absence of thyroid antibodies and clinical symptoms of autoimmune thyroid disease in at least two generations. We report here a Turkish family with a novel TSHr gene mutation with distinct features all consistent with ADNAH. Thyroid function tests of the proband were as follows: free T3: 13.1 pg/ml (N: 1.8–4.6); free T4: 5.1 ng/dl (N: 0.9–1.7); TSH: 0.01 μIU/ml (N: 0.2–4.2); and TSH receptor antibody: 2 IU/ml (N: 0–10). A heterozygous missense mutation in exon 10 of the TSHr gene (c.1454C>T) resulting in the substitution of valine for alanine at codon 485 (p.Ala485Val) was found in the father and his son and daughter. This mutation had arisen de novo in the father. Functional studies of the novel TSHr germline mutation demonstrated a higher constitutive activation of adenyl cyclase than wild type without any effect on phospholipase C activity. In conclusion, our data indicate that gain of function germline mutations in the TSHr gene should be investigated in families with members suffering from thyrotoxicosis and progressive growth of goiter, but without clinical and biochemical evidence of autoimmune thyroid disease. In addition, patients harboring the same mutation of the TSHr gene may show wide phenotypic variability with respect to the age at onset, and severity of hyperthyroidism and thyroid growth.     

Circulating Thyroid Antibodies in Congenital Hypothyroidism

ABSTRACT. The role of maternal thyroid antibodies in congenital hypotyroidism is controversial. We have analysed serum thyroid antibodies in patients and their mothers. In a bioassay, antibodies interacting with thyroid cells were analysed by measuring of TSH-stimulated CAMP production in a rat thyroid cell line, FRTLS. Serum antibodies against the TSH receptor, thyroid peroxidase and thyroglobulin were determined by radioreceptor assay and enzyme-linked immunosorbent assays. The bioassay was performed with IgG preparations from 89 mothers of children with congenital hypothyroidism. Analyses for TSH receptor antibodies and thyroid peroxidase/thyroglobulin antibodies were performed on 144 and 118 sera of newborn patients respectively. No evidence of an increased prevalence of thyroid antibodies was found on comparison with controls. One infant had transient neonatal hyperthyrotropinaemia because of TSH receptor blocking antibodies transferred from the mother. Our data indicate that, apart from transplacental transfer of TSH receptor antibodies, maternal immunoglobulins have a limited role in the aetiology of congenital thyroid dysfunction.     

A Case with Hyperthyroidism Who Had Been Treated with Thyroid Hormone Because of Congenital Hypothyroidism

We encountered a case with hyperthyroidism at the age of 14 who had been diagnosed with congenital hypothyroidism (CH) and had received thyroid hormone replacement therapy. At the age of 16 d, the patient was referred to our hospital because of positive results at neonatal screening for CH. Serum level of TSH was 91.0 μU/ml and serum level of T4 was 6.9 μg/dl. The patient was diagnosed as having hypothyroidism, and hormone replacement therapy was started. Thereafter the dosage of thyroid hormone was adjusted and increased gradually as he grew to a maximum dose of 110 μg/day at the age of 11. Until the age of 13, the patient’s serum levels of TSH were within the normal range; then, at the age of 13 yr and 4 mo, his serum level of TSH dropped to a level below the detectable range. The dosage of administered thyroid hormone was tapered off and eventually eliminated at the age of 14. A thyroid scan and a radioactive iodine uptake test demonstrated a diffuse goiter with homogeneous uptake of radioactive iodine; the uptake rate was 60% at 24 h, and the serum level of TSH receptor antibody (TRAb) was 62.5% at that time. Administration of an antithyroid drug was started after confirmation that our patient had developed hyperthyroidism. There have been no case reports similar to our case.     

Circulating thyroid antibodies in congenital hypothyroidism.

The role of maternal thyroid antibodies in congenital hypothyroidism is controversial. We have analysed serum thyroid antibodies in patients and their mothers. In a bioassay, antibodies interacting with thyroid cells were analysed by measuring of TSH-stimulated cAMP production in a rat thyroid cell line, FRTL5. Serum antibodies against the TSH receptor, thyroid peroxidase and thyroglobulin were determined by radioreceptor assay and enzyme-linked immunosorbent assays. The bioassay was performed with IgG preparations from 89 mothers of children with congenital hypothyroidism. Analyses for TSH receptor antibodies and thyroid peroxidase/thyroglobulin antibodies were performed on 144 and 118 sera of newborn patients respectively. No evidence of an increased prevalence of thyroid antibodies was found on comparison with controls. One infant had transient neonatal hyperthyrotropinaemia because of TSH receptor blocking antibodies transferred from the mother. Our data indicate that, apart from transplacental transfer of TSH receptor antibodies, maternal immunoglobulins have a limited role in the aetiology of congenital thyroid dysfunction.     

Pediatric thyroid testing issues

Thyroid problems are common in children. While serum thyroid function tests lead to an accurate diagnosis in most patients, unique patient situations can produce misleading results. Total T4 measurements can incorrectly suggest hypothyroidism in congenital thyroid binding globulin (TBG) deficiency and hyperthyroidism in TBG excess, as seen in high estrogen states. Free T4 (FT4) measurement techniques involve either physical separation of unbound thyroxine from serum binding proteins or estimation of FT4 levels in the presence of binding proteins. These estimation techniques are susceptible to under- or over-estimation of FT4 levels when binding proteins are low or high. Other complicating factors arise in the setting of prematurity or systemic non-thyroidal illness (NTI), simulating central hypothyroidism. Thyroid stimulating hormone (TSH) levels in children have a wider normal range than in adults and are affected by drugs and NTI. Additionally, heterophile and anti-T4 or anti-TSH antibodies can interfere with accurate T4 or TSH measurement.     

Borderline congenital hypothyroidism in the neonatal period

One of the most important etiological factors causing prolonged jaundice in the neonatal period is congenital hypothyroidism. Some infants may have abnormal thyroid function test results rather than overt congenital hypothyroidism. Although serum TSH levels are accepted as diagnostic when >20 microIU/l, TSH values higher than 7 microIU/ml cause a hypometabolic condition. In this study, we evaluated infants who had prolonged jaundice for hypothyroidism. A hundred and ten infants suffering from prolonged jaundice were admitted to our clinic during the study period. Among them, 61 infants had normal thyroid function results. Six patients had overt primary hypothyroidism. TRH stimulation test was administered to the 43 patients with mildly elevated TSH levels of between 5 and 20 microIU/ml. Peak TSH values were above 35 microIU/ml in seven patients, and these were considered as having an exaggerated response (borderline hypothyroidism). During the neonatal period, prolonged jaundice is a valuable diagnostic clue for hypothyroidism. In addition, the TRH stimulation test can be a diagnostic tool in evaluating infants with mildly abnormal thyroid function test results.     

Thyroid function in young children with Down syndrome

A retrospective review of thyroid function tests (TFTs) was performed on 49 young children (aged 4 months to 3 years) with Down syndrome compared with age-matched controls screened for hypothyroidism because of developmental delay or failure to thrive. Three of the 49 children with Down syndrome had congenital hypothyroidism; of the three, one had Hirschsprung's disease and two had duodenal atresia. Thyroiditis was uncommon, with only two children having thyroid antibodies present: one had acquired hypothyroidism and the other acquired hyperthyroidism. Twenty-seven percent of the Down syndrome cohort had mildly increased thyrotropin (TSH) and normal thyroxine levels. When compared with children with Down syndrome who had normal TFTs, no significant differences in sex, growth rate, maternal age, associated anomalies, developmental or specific thyroid symptoms were present. Transient elevations of TSH level were common in children with Down syndrome whether or not TSH values were initially normal or elevated. Routine neonatal and sequential thyroid screening in young children with Down syndrome is warranted.     

Resistance to thyroid hormone and its molecular basis

Generalized resistance to thyroid hormone (GRTH) is an inherited syndrome characterized by hyposensitivity of target tissues to thyroid hormone. The clinical presentation is variable. The syndrome is usually suspected when elevated serum thyroid hormone levels are associated with a non-suppressed thyroid-stimulating hormone (TSH). While goiter and thyroid test abnormalities have more often led to the suspicion of thyroid gland dysfunction, short stature, hyperactivity, learning disability and goiter in children or adolescents and recalcitrant goiter in adults, should raise the suspicion of GRTH. Hypothyroidism has been considered when growth or mental retardation was the presenting symptom and thyrotoxicosis when confronted with attention deficit, hyperactivity or tachycardia. Failure to recognize the inappropriate persistence of TSH secretion in spite of elevated thyroid hormone levels has commonly resulted in erroneous diagnosis leading to antithyroid treatment. More than 300 subjects with this syndrome have been identified. The mode of inheritance in the majority of families is autosomal dominant. Recessive transmission has been found in only one family. It has long been speculated that this defect is likely to be caused by an abnormal thyroid hormone receptor (TR), but this hypothesis could not be directly tested until the isolation of two TR genes, TRα and TRβ. Mutations in the TRβ gene have been identified in 42 families with GRTH. All are located in the T₃-binding domain straddling the putative dimerization region and exhibit various degrees of hormone-binding impairment. This finding, and the fact that heterozygous subjects with complete TR deletion are not affected while those with point mutations are, indicates that interactions of a mutant TR with normal TR and with other factors are responsible for the dominant inheritance of GRTH and its heterogeneity. Elucidation of the etiology of GRTH has not only added a new means for the early diagnosis of the syndrome but provided new insights in the understanding of the mechanism of hormone action.     

Maternal TSH-receptor antibodies and TSH antibodies in screening for congenital hypothyroidism

Serum samples from 30 mothers who had given birth to at least one child with a positive neonatal thyrotropin (TSH) screening test were analysed for TSH-receptor antibodies. One mother with hypothyroidism after thyroiditis who had two sons who had had transient congenital hypothyroidism, showed significantly elevated concentrations of TSH receptor blocking IgG antibodies in her serum. The three daughters of another mother had neonatal hyperthyrotropinaemia but normal thyroid hormone levels. This woman had elevated serum levels of TSH but was clinically and biochemically euthyroid. The apparent hyperthyrotropinaemia in this family was due to an artifact in the TSH radioimmunoassay caused by maternal anti-TSH IgG antibodies. It is obvious that placental transfer of maternal IgG antibodies to the thyroid TSH receptor is one cause of transient congenital hypothyroidism. Likewise, maternal IgG directed against TSH interferes with radioimmunoassays of TSH and the results may be falsely interpreted as hyperthyrotropinaemia. It is concluded that in neonatal hyperthyrotropinaemia analysis of the mother's serum is indicated, and that maternal TSH receptor blocking antibodies must be considered as a cause of congenital hypothyroidism, especially if the mother has a history of thyroid dysfunction.     

Maternal TSH-Receptor Antibodies and TSH Antibodies in Screening for Congenital Hypothyroidism

ABSTRACT. Serum samples from 30 mothers who had given birth to at least one child with a positive neonatal thyrotropin (TSH) screening test were analysed for TSH-receptor antibodies. One mother with hypothyroidism after thyroiditis who had two sons who had had transient congenital hypothyroidism, showed significantly elevated concentrations of TSH receptor blocking IgG antibodies in her serum. The three daughters of another mother had neonatal hyper-thyrotropinaemia but normal thyroid hormone levels. This woman had elevated serum levels of TSH but was clinically and biochemically euthyroid. The apparent hyperthyrotropinaemia in this family was due to an artifact in the TSH radioimmunoassay caused by maternal anti-TSH IgG antibodies. It is obvious that placental transfer of maternal IgG antibodies to the thyroid TSH receptor is one cause of transient congenital hypothyroidism. Likewise, maternal IgG directed against TSH interferes with radioimmunoassays of TSH and the results may be falsely interpreted as hyperthyrotropinaemia. It is concluded that in neonatal hyperthyrotropinaemia analysis of the mother's serum is indicated, and that maternal TSH receptor blocking antibodies must be considered as a cause of congenital hypothyroidism, especially if the mother has a history of thyroid dysfunction.     

Autoimmunthyreopathien bei Kindern und Jugendlichen mit Typ-1-Diabetes Häufigkeit und sinnvolles Screening

Background. Children and adolescents with type 1 diabetes are at increased risk for the development of autoimmune thyroid disease (Hashimoto thyroiditis and Grave's disease). Recommendations for screening have been very inconsistent. Method. Between 1996 and 1999, yearly determinations of serum TSH, fT4, fT3, thyroid peroxidase (TPO-) and thyroglobulin (Tg-) antibodies were done in 155 children and adolescents with diabetes. In those who were positive for thyroid antibodies and/or had a goiter thyroid sonography was performed. Specific therapy was instituted when overt hypo- or hyperthyroidism or subclinical hypothyroidism with goiter was present. No treatment was given to euthyroid patients who had positive thyroid antibodies but no goiter. Results. Between 1996 and 1999, autoimmune thyroiditis was diagnosed in 7 out of 155 children (all females). Hashimoto thyroiditis was present in 4, Grave's disease in 2 and thyroid antibody negative transient hyperthyroidism in one. Median age at diagnosis was 10.9 years, median duration of diabetes 3.1 years. The long-term course of thyroid autoantibody titers varied widely, there was no correlation with activity of hypo- or hyperthyroidism, predominant were TPO- antibodies. Four euthyroid children had elevated thyroid antibodies only, none developed a goiter or thyroid dysfunction so far. One child had subclinical hypothyroidism without thyroid antibodies and was treated with iodine. Of note were markedly increased HbA1c levels coincident with overt hyperthyroidism which decreased once euthyroidism was achieved. Conclusion. Routine screening for autoimmune thyroid disease in children and adolescents with diabetes is necessary. At onset of diabetes, thyroid function and antibodies should be determined to identify patients at risk. During follow-up, search for symptoms and signs of hypo- or hyperthyroidism or goiter as well as a determination of TSH once yearly is sufficient. If abnormal findings are present an extended work-up is necessary (see Fig. 1). Unexplained high HbA1c levels may be caused by unrecognised hyperthyroidism.     

TSH-secreting pituitary macroadenoma in an 11-year-old girl

Graves' disease, multinodular toxic goiter or toxic adenoma are the usual causes of hyperthyroidism in children as well as in adults. We report a case of hyperthyroidism due to TSH-secreting pituitary macroadenoma in an 11-year-old girl. The patient was admitted to the Endocrine Department for pituitary function evaluation, five months after transfrontal adenomectomy and pituitary irradiation for a macroadenoma. On admission the patient was clinically hyperthyroid and the work-up established a diagnosis of hyperthyroidism due to TSH-secreting adenoma (high levels of TSH in the face of hyperthyroidism, no TSH response to TRH stimulation, diffuse thyroid goiter without eye signs or pretibial myxedema). Of interest in this case was the fact that: (a) she is the youngest patient reported with hyperthyroidism due to a TSH-secreting macroadenoma and (b) hyperthyroidism was diagnosed after adenomectomy.     

Thyroid function and puberty

Thyroid hormones are essential for normal growth, sexual development and reproductive function. During puberty, changes in thyroid functions and an increase in thyroid volume occur as an adaptation to body and sexual development. Hypothyroidism diagnosed late in prepubertal years, usually due to Hashimoto's thyroiditis, can cause a delay of puberty or incomplete isosexual precocity (development of breast and internal genitalia in girls and increased testis volume in boys without adrenarche). In contrast, normal pubertal development and adequate menarche have been documented in congenital hypothyroidism detected by neonatal screening and treated early. The effect of hyperthyroidism on pubertal development is not well known, but a short period of hyperthyroidism seems not to have major negative effects. In adolescence or young adulthood, menstrual dysfunction, infertility, and stillbirth or premature birth are associated with thyroid dysfunction.