Congenital hypothyroidism

Mother's iodine exposure and infants' hypothyroidism: the Japan Environment and Children's Study (JECS)

In this study, we aimed to determine the association of neonatal/post-neonatal hypothyroidism with mother's iodine exposure, especially povidone iodine disinfection, and hysterosalpingography. Participants were mother-child pairs in a Japanese birth cohort (n = 100,286). Risk factors of hypothyroidism were supplement intake, seaweed intake, other daily iodine intake, povidone iodine disinfection at delivery, and maternal history of hysterosalpingography, thyroid disease (Graves' disease and Hashimoto's thyroiditis), and medication (thiamazole and levothyroxine). Congenital hypothyroidism (CH) at age 1 year was assessed using a questionnaire. Transient hypothyroidism was defined as elevated thyroid stimulating hormone level at birth and absence of CH at age 1 year. The incidence of CH at age 1 year per 100 children was 1.1 for those born at 22-30 weeks' gestation, 0.17 following povidone iodine disinfection, and 0.07, 0.95, 0.81, 1.17, and 1.15 with a maternal history of hysterosalpingography, Graves' disease, Hashimoto's thyroiditis, thiamazole use, and levothyroxine use, respectively. Odds ratios (95% confidence intervals) of CH at age 1 year for povidone iodine disinfection, hysterosalpingography history, maternal Graves' disease, and maternal Hashimoto's thyroiditis were 1.13 (0.71-1.79), 0.47 (0.07-3.36), 7.06 (3.70-13.5), and 5.93 (2.90-12.1), respectively. For transient hypothyroidism for povidone iodine disinfection and hysterosalpingography history, these values were 1.99 (1.51-2.62) and 0.63 (0.20-1.96), respectively. Maternal thyroid disease greatly increased neonatal/post-neonatal hypothyroidism risk. Povidone iodine disinfection may increase transient hypothyroidism risk but not the risk at 1 year of age. Hysterosalpingography does not increase hypothyroidism risk from birth to age 1 year.

The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR

1) Background: Central congenital hypothyroidism (CCH) is a rare endocrine disorder that can be caused by mutations in the β-subunit of thyrotropin (TSHB). The TSHB mutation C105Vfs114X leads to isolated thyroid-stimulating-hormone-(TSH)-deficiency and results in a severe phenotype. The aim of this study was to gain more insight into the underlying molecular mechanism and the functional effects of this mutation based on two assumptions: a) the three-dimensional (3D) structure of TSH should be modified with the C105V substitution, and/or b) whether the C-terminal modifications lead to signaling differences. 2) Methods: wild-type (WT) and different mutants of hTSH were generated in human embryonic kidney 293 cells (HEK293 cells) and TSH preparations were used to stimulate thyrotropin receptor (TSHR) stably transfected into follicular thyroid cancer cells (FTC133-TSHR cells) and transiently transfected into HEK293 cells. Functional characterization was performed by determination of Gs, mitogen activated protein kinase (MAPK) and Gq/11 activation. 3) Results: The patient mutation C105Vfs114X and further designed TSH mutants diminished cyclic adenosine monophosphate (cAMP) signaling activity. Surprisingly, MAPK signaling for all mutants was comparable to WT, while none of the mutants induced PLC activation. 4) Conclusion: We characterized the patient mutation C105Vfs114X concerning different signaling pathways. We identified a strong decrease of cAMP signaling induction and speculate that this could, in combination with diverse signaling regarding the other pathways, accounting for the patient's severe phenotype.

Segregation of S292F TPO gene mutation in three large Tunisian families with thyroid dyshormonogenesis: evidence of a founder effect

We aimed to identify causal mutation(s) in 13 patients with thyroid dyshormonogenesis (TD) from three consanguineous Tunisian families. A 12-year clinical follow-up showed phenotypic variability ranging from the presence to the absence of goiter, sensorineural deafness, and mental retardation. Genetic analysis using microsatellite markers within two candidate genes (TPO and PDS) gave evidence of linkage with the TPO gene. Sequencing of its 17 exons and their flanking intron-exon junctions revealed the previously described c.875C>T (p.S292F) mutation in homozygous state. No additional mutations were found in either a 900 bp of the TPO gene promoter or PDS gene. In silico analysis showed that p.S292F mutation might reduce the catalytic cavity of the TPO which would restrict access of a potential substrate to the catalytic pocket. Using 4SNPs and one microsatellite marker in the TPO gene, an associated haplotype: G-C-G-G-214 was found, giving evidence of a founder mutation.

CONCLUSION

This is the first description of a TD causing mutation in Tunisia and thus may help to develop a genetic screening protocol for congenital hypothyroidism in the studied region. Although structural modeling suggested a pathogenic effect of this mutation, functional studies are needed. Additional causing and/or modifier genes, together with late diagnosis could explain the clinical variability observed in our patients.

A Novel, Homozygous c.1502T>G (p.Val501Gly) Mutation in the Thyroid peroxidase Gene in Malaysian Sisters with Congenital Hypothyroidism and Multinodular Goiter

Congenital hypothyroidism (CH) with multinodular goiter (MNG) is uncommonly seen in children. However, CH associated with goiter is often caused by defective Thyroid peroxidase (TPO) gene. In this study, we screened for mutation(s) in the TPO gene in two siblings with CH and MNG and their healthy family members. The two sisters, born to consanguineous parents, were diagnosed with CH during infancy and received treatment since then. They developed MNG during childhood despite adequate L-thyroxine replacement and negative thyroid antibody screening. PCR-amplification of all exons using flanking primers followed by DNA sequencing revealed that the two sisters were homozygous for a novel c.1502T>G mutation. The mutation is predicted to substitute valine for glycine at a highly conserved amino acid residue 501 (p.Val501Gly). Other healthy family members were either heterozygotes or mutation-free. The mutation was not detected in 50 healthy unrelated individuals. In silico analyses using PolyPhen-2 and SIFT predicted that the p.Val501Gly mutation is functionally "damaging." Tertiary modeling showed structural alterations in the active site of the mutant TPO. In conclusion, a novel mutation, p.Val501Gly, in the TPO gene was detected expanding the mutation spectrum of TPO associated with CH and MNG.

[Newborn Screening Program for congenital hypothyroidism of the State of Santa Catarina, Brazil: etiological investigation in the first visit]

OBJECTIVE

To evaluate the etiology of primary congenital hypothyroidism (PCH) identified in the Newborn Screening Program from the state of Santa Catarina, Brazil, from July 2007 to June 2009 in the first visit.

SUBJECTS AND METHODS

A prospective study was performed in 45 patients with PCH. For the etiological diagnosis, history, physical examination, and additional tests (TSH, free thyroxine, thyroglobulin, bone age assessment, thyroid ultrasound) were carried out in the first visit.

RESULTS

The etiology was established in the first visit in 53.3% of cases. Thyroid dysgenesis represented 51.11% of the cases, from which 20% showed hypoplastic thyroid, 13.3% showed athyreosis, and 17.7% showed ectopic glands; 2.2% were diagnosed with dyshormonogenesis. Umbilical hernia was the most prevalent sign (48.89%) and 20% had no clinical manifestations. Patients with dysgenesis showed significant differences (p < 0.05) in terms of cesarean section delivery, delayed bone age, and very high serum TSH.

CONCLUSIONS

The diagnostic approach used at first visit for PCH patients may determine the etiology in 53.3% of cases. Half of patients had thyroid dysgenesis.

A Novel Hypothyroid Dwarfism Due to the Missense Mutation Arg479Cys of the Thyroid Peroxidase Gene in the Mouse

Recently, we found a novel dwarf mutation in an ICR closed colony. This mutation was governed by a single autosomal recessive gene. In novel dwarf mice, plasma levels of the thyroid hormones, T3 and T4, were reduced; however, TSH was elevated. Their thyroid glands showed a diffuse goiter exhibiting colloid deficiency and abnormal follicle epithelium. The dwarfism was improved by adding thyroid hormone in the diet. Gene mapping revealed that the dwarf mutation was closely linked to the thyroid peroxidase (Tpo) gene on chromosome 12. Sequencing of the Tpo gene of the dwarf mice demonstrated a C to T substitution at position 1508 causing an amino acid change from arginine (Arg) to cysteine (Cys) at codon 479 (Arg479Cys). Western blotting revealed that TPO protein of the dwarf mice was detected in a microsomal fraction of thyroid tissue, but peroxidase activity was not detected. These findings suggested that the dwarf mutation caused a primary congenital hypothyroidism by TPO deficiency, resulting in a defect of thyroid hormone synthesis.

Contribution of genetic factors to neonatal transient hypothyroidism

BACKGROUND

The causes of neonatal transient hypothyroidism (NTH) remain incompletely understood. Whether it is influenced by genetic background is rarely discussed and remains unproven. A defect in thyroid peroxidase is a common cause of dyshormonogenesis of the thyroid gland in Taiwanese, with a novel mutation (2268insT) present in nearly 90% of alleles studied.

OBJECTIVE

To determine if the presence of this common mutation is associated with NTH in Taiwan.

METHODS

A mismatched primer was designed and used for this specific 2268insT mutation to screen 1000 normal babies and 260 babies with confirmed NTH.

RESULTS

The carrier rate for 2268insT in normal babies (1/200) was significantly lower than in babies with NTH (1/13; p<0.0001).

CONCLUSIONS

The results strongly suggest that the presence of this thyroid peroxidase mutation contributes to the development of NTH. Likely pathogenetic explanations include the effect of the stress of extrauterine adaptation during labour on an immature pituitary-thyroid axis in genetically predisposed individuals, combined with environmental triggers such as iodine deficiency, perinatal iodine exposure, and/or goitrogen contamination.

Comparative analysis and characterization of mutated thyroid peroxidases with disturbance expressed on the cell surface

Five mutated thyroid peroxidases (TPO) with varying degrees of disturbance in cell surface expression, probably owing to misfolding, were comparatively analyzed. CHO-K1 cells transfected with these mutated mRNAs expressed TPO protein in 65.6-82.1% of cells in antibody staining, and the TPOs were located in intracellular structures like the nuclear envelope and ER as well as cytoplasmically like wild-type TPO. When cell surface expression was examined, three mutated TPOs, G533C-, D574/L575del-, and G771R-TPOs, were expressed to varying degrees. In contrast, R175Q- and R665W-TPOs were thought not to be expressed on the cell surface, although a vague increment in R175Q-TPO was observed with increasing amounts of mRNA. In the kinetic study, three mutated TPOs having insufficient expression on the cell surface showed delays in decrease at 4 and 8 h after chase, although between 8 and 24 h after chase they decreased rapidly, as did the two other mutated TPOs. In immunoprecipitation by anti-TPO antibody, G533C-, D574/L575del-, and G771R-TPOs exhibited increasing interaction with calnexin. The combined evidence suggested that some of the mutated TPOs with disturbance in cell surface expression, probably owing to misfolding, exhibited the delay in kinetics of newly synthesized protein as a result of increasing interaction with calnexin and that such TPOs could be expressed to some extent on the cell surface.

A Novel Missense Mutation in the Thyroid Peroxidase Gene, R175Q, Resulting in Insufficient Cell Surface Enzyme in Two Siblings

Thyroid peroxidase (TPO) abnormality is one of the causes of congenital hypothyroidism. Two missense mutations were found as a compound heterozygous mutation in two siblings with congenital goitrous hypothyroidism. One of these mutations, G614A (R175Q), was a novel mutation. Characterization of the novel mutation and a cotransfection experiment with two mutated TPO mRNAs were carried out. G614A-mRNA introduced into CHO-K1 cells expressed TPO protein with the same molecular weight as that of wild-type mRNA. The R175Q-TPO was thought to possess enzyme activity. In terms of localization, a very small amount of mutated TPO was expressed on the plasma membrane of CHO-K1 cells. This plasma membrane expression of R175Q-TPO was insufficient to perform thyroid hormone synthesis, but was markedly different from R665W-TPO. When G614A- and C2083T-mRNAs were cotransfected, cell surface TPO-positive cells were only 13.1% in contrast to 54.4% for wild-type mRNA. The low positivity and intensity of cell surface TPO suggested that in the patients’ thyroids thyroid hormone synthesis was hardly performed. The congenital hypothyroidism of the patients was thought to be a result of the mutations of the TPO gene (G614A/C2083T).

The call from the newborn screening laboratory: frustration in the afternoon

Newborn screening programs in the United States are evolving in concert with technologic advances in analytic chemistry and medicine. Many more disorders are being identified on dried filter paper blood spots without fundamentally altering the basic principles first put forward in the 1960s. Some disorders have been added without researchers knowing if there is a true benefit to early diagnosis and treatment; some disorders currently being detected will merit little or no follow-up in the future. The general principles underlying newborn screening are discussed, as are the individual disorders screened in most programs. The expanding and evolving impact of tandem mass spectrometry on newborn screening is also explored.

Werdnig-Hoffmann disease with congenital hypothyroidism

Congenital hypothyroidism is often associated with other congenital anomalies. In some instances it is difficult to differentiate congenital hypothyroidism from Werdnig-Hoffmann's disease. We report a case of congenital hypothyroidism associated with Werdnig-Hoffmann's disease that appears to be the first of its kind in the literature.

Partial iodide organification defect caused by a novel mutation of the thyroid peroxidase gene in three siblings

BACKGROUND

Three siblings with goitre and latent to mild hypothyroidism were suspected of having thyroid peroxidase (TPO) abnormality. Direct sequencing of their genomic DNAs showed two novel mutations of the TPO gene, one of which was G1687T (Gly533Cys; exon 9) and the other 1808-13del (Asp574/Leu575del; exon 10). The two mutations were compound heterozygous, as the former was found in their father's DNA as heterozygous, and the latter was found in DNA from their mother, also as heterozygous. As Gly533 and Asp574/Leu575 were well-conserved amino acids in the peroxidase superfamily, Gly533Cys- and Asp574/Leu575del-TPOs were thought to be affected structurally or functionally. In expression studies using CHO-Kl cells and mRNAs introduced with individual mutations, both mutated TPO proteins were expressed at the same molecular size as wild-type TPO and had enzyme activity, although Gly533Cys-TPO was slightly lower in efficiency of expression and more degenerative than wild-type TPO.

METHODS

We examined the localization of both mutated TPOs. Gly533Cys-TPO was located on the endoplasmic reticulum (ER) and nuclear envelope but not on the plasma membrane, whereas Asp574/Leu575del-TPO was located not only on the ER and nuclear envelope but also on the plasma membrane, as wild-type TPO. Nevertheless, only one point differed between Asp574/Leu575del- and wild-type TPOs: the mutated TPO was expressed on the plasma membrane surface at less than half the rate of wild-type TPO.

RESULTS

Gly533Cys-TPO synthesized almost no thyroid hormone because of its defective localization on the apical membrane surface of thyrocytes, whereas Asp574/Leu575del-TPO performed thyroid hormone synthesis at a rate of less half that of wild-type TPO. In cotransfection experiments using three combinations of wild-type and G1687T-mRNAs, wild-type and 1808-13del-mRNAs, and G1687T-, 1808-13del-mRNAs, the three kinds of mRNAs were considered to have no influence on cell surface TPO expression of another mRNA when a 50%-maximal amount of each mRNA was transfected. When a larger amount of each mRNA was transfected, the former two combinations showed the level of cell surface TPO expression obtained from the saturating amount of wild-type mRNA, whereas the last combination of mutated mRNAs covered only about half of the expression level.

CONCLUSION

Defective thyroid hormone production resulting from the abnormal TPOs was at a level that caused latent hypothyroidism when the patients were born. With their growth, thyroid hormone volume gradually became inadequate and their thyroid gland enlarged compensatorily.

Lack of a relation between human neonatal thyroxine and pediatric neurobehavioral disorders

The growth and differentiation of the central nervous system are closely related to the presence of iodine and thyroid hormones. It has been hypothesized that neurobehavioral disabilities of childhood, such as attention deficit hyperactivity disorder (ADHD), learning disorders, and autism can be attributed to fetal thyroidal endocrine disruption in utero. To determine whether there is an association between neonatal thyroid status and a subsequent diagnosis of a neurobehavioral disability, neonatal thyroxine (T(4)) levels have been used as the indicator of the presence of intrauterine thyroidal dysfunction. Neonatal T(4) levels were obtained from the neonatal hypothyroidism screening program. All cases were diagnosed at medical school diagnostic clinics, the diagnostic categories being ADHD, autism spectrum disorder, behavioral disorder, cognitive disorder, developmental delay, emotional disorder, learning disability, and speech/language disorder. Conditional logistic regression analysis was performed for each clinical condition. Odds ratios for the conditions ranged from 0.92 to 1.13 with p values ranging between 0.19 and 0.84. No significant differences were detected between neonatal T(4) values of the cases and the controls for any of the neurobehavioral conditions. All neonatal T(4) values were within normal ranges. The data provide no evidence to suggest that intrauterine thyroid status as reflected by the neonatal T(4) values had an impact on the neurologic disorders diagnosed in childhood.

Clinical utility of thyroid ultrasonography in the diagnosis of congenital hypothyroidism

To determine the clinical utility of thyroid ultrasonography in the diagnosis of congenital hypothyroidism (CH) before initiation of therapy, ultrasonographic images of the thyroid gland with a high-resolution transducer were obtained in 204 healthy infants aged from newborn to 12 months (Group A), and 174 infants suspected of having CH detected by neonatal mass screening (Group B). The thyroid gland was imaged by transverse scanning at the anatomic site of the thyroid gland. The maximal width of thyroid on the transverse section in the normal location was measured. By comparing with the normal thyroid gland size and location obtained from Group A, 174 infants of Group B were divided into four subgroups: 1) Normal in size (n = 117), 2) Enlarged (n = 33), 3) Small (n = 1) and 4) Invisible in the normal location (n = 23). They were compared with the final diagnoses based on the results of chemical laboratory data and scintigraphic findings. The sensitivity and the specificity for the presence or absence of the thyroid gland in the normal location were 96% (22/23) and 99% (150/151), respectively. Both subgroups of normal and enlarged sized gland included healthy infants (false positive), transient hyperthyrotropinaemia, transient hypothyroidism and CH due to dyshormonogenesis. We conclude that ultrasonography is useful for determining the presence or absence of the thyroid gland in the normal location, whereas normal and enlarged sized glands require further examination to complete the diagnosis.

Newborn thyroxine levels and childhood ADHD

OBJECTIVES

Normal brain development is highly dependent on adequate levels of iodine and thyroid hormone. It has been suggested that Attention Deficit Hyperactivity Disorder (ADHD) is the consequence of prenatal thyroidal endocrine disruption. The hypothesis was examined using neonatal thyroxine levels as a bio-marker of prenatal thyroid status and comparing it to subsequent development of ADHD.

DESIGN AND METHODS

In a matched case-control study, cases were defined as children diagnosed with ADHD, while children born in the same hospital and tested on the same day served as matched controls. Conditional logistic regression analysis with unequal numbers of controls was performed.

RESULTS

The neonatal thyroxine levels were within normal limits for each of the children who were subsequently diagnosed as having ADHD, and their distribution was no different from that of their controls.

CONCLUSIONS

Children diagnosed with ADHD do not demonstrate prenatal thyroidal dysfunction as reflected in the newborn thyroxine levels, therefore neonatal thyroxine levels are not a bio-marker for the subsequent development of ADHD.

Genetic screening of newborns

Screening of newborn infants for genetic disease began over 35 years ago as a public health measure to prevent mental retardation in phenylketonuria (PKU). It was so successful that tests for several other genetic disorders were added. We review the current status of this screening, including discussions of the genetic disorders often covered and the results of newborn screening for them. We emphasize recent advances. These include expansion of coverage for genetic disorders with the new methodology of tandem mass spectrometry (MS-MS) and the introduction of molecular (DNA) testing to increase the specificity of testing for several disorders, thereby reducing false-positive rates. These and other advances have also produced issues of criteria for screening, missed cases, and appropriate use of stored newborn specimens.

Triagem neonatal de distúrbios metabólicos

Diversos distúrbios metabólicos que se manifestam de forma grave e precoce podem ter sua história natural substancialmente alterada pela introdução de um tratamento em sua fase pré-clínica. O diagnóstico pré-sintomático só é possível com a realização de testes de triagem populacional em recém-nascidos. O esforço para realizar um programa de triagem neonatal deve ser empreendido quando um distúrbio metabólico preenche os seguintes requisitos: 1) o distúrbio traz, se não tratado, conseqüências graves para a saúde do afetado; 2) existe um tratamento que pode modificar substancialmente a história natural da doença; 3) o tratamento é significativamente mais eficaz quando implantado na fase pré-clínica da doença; 4) existe um teste de triagem que seja simples, eficiente, aplicável em larga escala e de baixo custo. Baseados nessas premissas, programas de triagem neonatal foram inicialmente implantados para fenilcetonúria e hipotireoidismo congênito, e hoje estão sendo aplicados para um número crescente de situações. Esses programas já estão bem-consolidados nos países desenvolvidos, mas é ainda um desafio a sua eficiente aplicação nos países do Terceiro Mundo.

Cloning, chromosomal localization and identification of polymorphisms in the human thyroid transcription factor 2 gene (TITF2)

The human gene encoding the thyroid transcription factor 2 (TTF-2) was cloned and mapped to human chromosome 9q22. Three polymorphisms were identified in the gene by SSCP and direct sequencing: two consist of a third base substitution in the triplet encoding Leu129 and Ser273, and the third is an alanine stretch that varies from 12 to 17 residues. TTF-2 plays a critical role during thyroid morphogenesis in mice, and in man the TITF2 gene is associated with congenital hypothyroidism and cleft palate with thyroid dysgenesis. The polymorphisms identified in this study can be used as markers to study the role of the TITF2 gene in other cases of thyroid dysgenesis, especially in familial cases.

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.

Congenital hypothyroidism due to mutations in the sodium/iodide symporter. Identification of a nonsense mutation producing a downstream cryptic 3' splice site

A 12-yr-old hypothyroid girl was diagnosed at birth as athyreotic because her thyroid gland could not be visualized by isotope scanning. Goiter development due to incomplete thyrotropin suppression, a thyroidal radioiodide uptake of < 1%, and a low saliva to plasma ratio of 2.5 suggested iodide (I-) transport defect. mRNA isolated from her thyroid gland and injected into Xenopus oocytes failed to increase I- transport. Sequencing of the entire Na+/I- symporter (NIS) cDNA revealed a C to G transversion of nucleotide (nt) 1146 in exon 6, resulting in a Gln 267 (CAG) to Glu (GAG) substitution. This missense mutation produces an NIS with undetectable I- transport activity when expressed in COS-7 cells. Although only this missense mutation was identified in thyroid and lymphocyte cDNA, genotyping revealed that the proposita and her unaffected brother and father were heterozygous for this mutation. However, amplification of cDNA with a primer specific for the wild-type nt 1146 yielded a sequence lacking 67 nt. Genomic DNA showed a C to G transversion of nt 1940, producing a stop codon as well as a new downstream cryptic 3' splice acceptor site in exon 13, responsible for the 67 nt deletion, frameshift, and premature stop predicting an NIS lacking 129 carboxy-terminal amino acids. This mutation was inherited from the mother and present in the unaffected sister. Thus, although the proposita is a compound heterozygote, because of the very low expression (< 2.5%) of one mutant allele, she is functionally hemizygous for an NIS without detectable bioactivity.

Mutations in the gene encoding thyroid transcription factor-1 (TTF-1) are not a frequent cause of congenital hypothyroidism (CH) with thyroid dysgenesis

Permanent congenital hypothyroidism (CH) has an incidence of 1/3000-4000 newborns and is among the most frequent cause of mental retardation and neurological alterations in children. In 80% to 85% of cases CH is associated with thyroid dysgenesis. A group of 61 patients with CH (22 with agenesis, 18 with ectopy, 1 with hypoplasia, and 20 cases with CH without thyroid enlargement but not further characterized) and 30 normal subjects were examined for the presence of mutations in the gene encoding the thyroid transcription factor 1 (TTF-1). The coding-region of the TTF-1 gene was analyzed in all cases by the single stranded conformational polymorphism (SSCP) and no mutations were detected. Direct sequencing also carried out in patients with thyroid agenesis confirmed the absence of mutations or polymorphisms in the TTF-1 gene. The absence of mutations in the TTF-1 gene in our samples indicates that the mutations in the TTF-1 gene are not a frequent cause of CH.

Screening for metabolic disorders. How are we doing?

Routine screening for phenylketonuria and congenital hypothyroidism has become an integral part of pediatric practice in the United States. Screening for several other metabolic disorders is now entering the second or third decade of use. New information is available for the pediatrician for both groups of disorders that will be of help in caring for children in the years to come.