Positive Perchlorate Discharge Test Research Articles

The Relationship Between Iodine Status and Thyroid Function in Congenital Hypothyroidism With Eutopic Thyroid Gland

Abstract Background: We investigated the relationship between iodine status and thyroid function in children with congenital hypothyroidism (CH) with eutopic gland. We also evaluated whether the presence of iodine organification defect (IOD) or pathogenic genetic variants affects the association between iodine status and thyroid function. Methods: A total of 31 children (14 boys) with CH participated in the study, who repeatedly underwent thyroid function test and urine iodine concentration (UIC) without levothyroxine (LT4) medication after 3 years of age (1-5 times per patient). After confirming eutopic gland, IOD was demonstrated by the positive perchlorate discharge test with a discharge rate >10%. Genetic analysis was performed using targeted gene sequencing including 23 genes. Results: We identified likely pathogenic or pathogenic variants in 14 cases (45.2%): 1 case with triallelic (digenic) variants (DUOX2 and TSHR), 4 cases with biallelic variants (3 DUOX2 and 1 TSHR), and 9 cases with monoallelic variants (7 DUOX2, 1 DUOXA2, and 1 TSHR). Among 26 cases treated with LT4 from neonatal period, thyroid function after LT4 discontinuation was euthyroid (n = 7), subclinically hypothyroid (n=15), and overtly hypothyroid requiring LT4 (n = 3). The other 5 cases without LT4 treatment remained subclinical hypothyroid. After excluding 2 cases with TSHR, 29 cases (with 72 samples) were included to analyze the relationship between iodine status and log-transformed TSH (log-TSH) using generalized estimating equation models. The positive IOD (n = 17) was not associated with presence of DUOX2/DUOXA2 variants (n = 12). Iodine status of urine samples was categorized into adequate (UIC < 300 μg/L, n = 25), mild excessive (UIC = 300-599 μg/L, n = 14), and severe excessive (UIC ≥ 600 μg/L, n = 33) groups. When stratified by the presence of IOD, log-TSH significantly increased in severe excessive group (β = 0.52, P = 0.014 vs. iodine adequate group) among negative IOD group, but rather decreased in mild excessive group (β = -0.84, P < 0.001 vs. iodine adequate group) among positive IOD group. Meanwhile, when stratified by the presence of DUOX2/DUOXA2 variants, no significant association was found between iodine status and log-TSH levels. Conclusion:DUOX2 mutation was most common in CH patients with eutopic gland. The relationship of iodine status with thyroid function differed by presence of IOD.

Genetic defects of hydrogen peroxide generation in the thyroid gland.

Hydrogen peroxide (H2O2) is a key element in thyroid hormone biosynthesis. It is the substrate used by thyroid peroxidase for oxidation and incorporation of iodine into thyroglobulin, a process known as organification. The main enzymes composing the H2O2-generating system are the dual oxidase 2 (DUOX2) and the recently described DUOX maturation factor 2 (DUOXA2). Defects in these reactions lead to reduced thyroid hormone synthesis and hypothyroidism, with consequent increased TSH secretion and goiter. Since the first report in 2002 of DUOX2 mutations causing congenital hypothryoidism (CH), to date 25 different mutations have been described. Affected patients show a positive perchlorate discharge test and high phenotypic variability, ranging from transient to permanent forms of CH. Up to now, only two cases of CH due to DUOXA2 defects have been published. They also suggest the existence of a great genotype-phenotype variability. The phenotypic expression is probably influenced by genetic background and environmental factors. DUOX and DUOXA constitute a redundant system in which DUOX1/DUOXA1 can at least partially replace the function of DUOX2/DUOXA2. Furthermore, increased nutritional iodide could ensure a better use of H2O2 provided by DUOX1.

Congenital goitrous hypothyroidism, deafness and Iodide organification defect in four siblings: Pendred or pseudo-pendred syndrome?

Pendred syndrome (PDS) is an autosomal recessive disorder characterized by congenital deafness, goiter and iodide organification defect. Presence of inner ear malformations is essential for the clinical diagnosis. Most individuals with PDS are clinically and biochemically euthyroid. Mutations in the PDS gene encoding pendrin protein have been shown to be associated with PDS. It has been recently demonstrated that some families with features of PDS do not have the inner ear malformations and mutations in the PDS gene. This condition has been named as “pseudo−Pendred syndrome” (pseudo−PDS), and has been hypothesized to be of autoimmune origin. Here we report four siblings who have goiter, severe hypothyroidism, a positive perchlorate discharge test and sensorineural deafness, but not the inner ear abnormality which is diagnostic for PDS. We suggest that thyroid peroxidase (TPO) gene should be analyzed in pseudo−PDS patients with congenital goitrous hypothyroidism and deafness.Conflict of interest:None declared.

Identification of SLC26A4 gene mutations in Iranian families with hereditary hearing impairment

Mutations in the SLC26A4 gene at the DFNB4 locus are responsible for Pendred syndrome and non-syndromic hereditary hearing loss (DFNB4). This study included 80 nuclear families with two or more siblings segregating presumed autosomal recessive hearing loss. All deaf persons tested negative for mutations in GJB2 at the DFNB1 locus and were, therefore, screened for autozygosity by descent (ABD) using short tandem repeat polymorphisms (STRPs) that flanked SLC26A4. In 12 families, homozygosity for STRPs suggested possible ABD in this genomic region. Affected individuals in five families had a positive perchlorate discharge test. Sequence analysis of SLC26A4 identified ten mutations in eight families (T420I, 1197delT, G334V, R409H, T721M, R79X, S448L, L597S, 965insA and L445W), of which, four are novel (T420I, G334V, 965insA and R79X). These results imply that Pendred syndrome is the most prevalent form of syndromic hereditary hearing loss in Iran.

Analysis of the SLC26A4 gene in patients with Pendred syndrome in Taiwan

Pendred syndrome (PS) is an autosomal recessive disease that is characterized by congenital sensorineural hearing loss, goiter, and a partial iodine organification defect. In this study, we characterized the thyroid status and identified mutations in the SLC26A4 gene in Chinese subjects with PS. We evaluated 7 unrelated Chinese subjects who had PS. Biochemical analysis, formal audiogram, ultrasonography of the thyroid gland, perchlorate discharge test, computerized tomography scan of the vestibular aqueducts, and DNA sequence analysis of SLC26A4 were performed. Levels of thyroid hormones were essentially normal in all patients: 2 patients had goiters and/or elevated serum thyroglobulin levels, whereas 2 other patients had positive thyroid antibodies and a positive perchlorate discharge test. We identified SLC26A4 gene mutations in 6 of 7 probands and their affected relatives. The affected subjects in family I was compound heterozygous for 2 missense mutations: a mutation in exon 9 (1079C>T) that resulted in the replacement of alanine by valine at codon 360 (A360V) and a mutation in exon 19 (2168A>G) that resulted in the replacement of histidine by arginine at codon 723 (H723R). The affected subjects in families II and III all were homozygous for a mutation in intron 7. The probands IV and V were compound heterozygotes for the mutation in intron 7 and in exon 19, and the proband VI was compound heterozygous for the intron 7 mutation and a missense mutation in exon 12 (1343C>T) that resulted in the replacement of serine by leucine at codon 448 (S448L). One novel mutation was identified (A360V). We identified biallelic mutations in the SLC26A4 gene in 6 of 7 probands with PS in Taiwan, including a novel missense mutation. The mild thyroid dysfunction in these patients suggests that PS should be considered in all patients with congenital or early-onset hearing impairment.

Two compound heterozygous mutations (c.215delA/c.2422T→C and c.387delC/c.1159G→A) in the thyroid peroxidase gene responsible for congenital goitre and iodide organification defect

Iodide organification defects are frequently but not always associated with mutations in the thyroid peroxidase (TPO) gene and characterized by a positive perchlorate discharge test. These mutations phenotypically produce a congenital goitrous hypothyroidism, with an autosomal recessive mode of inheritance. In the present study we extended our initial molecular studies in six unrelated patients heterozygous for the TPO mutations, in order to identify the second mutation in this autosomal recessive disease. The promoter and the complete coding regions of the human TPO and DUOXA2 genes, along with the flanking regions of each intron were analysed by direct DNA sequencing. Four different inactivating TPO mutations were identified in two patients: two novel mutations (c.215delA [p.Q72fsX86] and c.1159G-->A [p.G387R]) and two previously reported (c.387delC [p.N129fsX208] and c.2422T-->C [p.C808R]), confirming the inheritance of two different compound heterozygous mutations, c.215delA/c.2422T-->C and c.387delC/c.1159G-->A. The remaining four patients did not show additional inactivating mutations in the TPO gene and all had only the wild type sequencing in the DUOXA2 gene. We have reported two patients with iodide organification defect caused by two compound heterozygous mutations, c.215delA/c.2422T-->C [p.Q72fsX86/p.C808R] and c.387delC/c.1159G-->A [p.N129fsX208/p.G387R], in the TPO gene and four patients with monoallelic TPO defect. Identification of the molecular basis of this disorder might be helpful for understanding the pathophysiology of congenital hypothyroidism.

Clinical and genetic characteristics of congenital hypothyroidism due to mutations in the thyroid peroxidase (TPO) gene in Israelis

Iodide organification defect (IOD) is characterized by a reduced ability of the thyroid gland to retain iodide and results in hypothyroidism. Mutations in the thyroid peroxidase (TPO) gene are a frequent cause of IOD. While TPO mutations have been identified in various populations, none have been reported in Israeli patients with IOD. The objectives of this study were to characterize the molecular basis of IOD in an Israeli Arab-Muslim population and to analyse the clinical, neurological and imaging data of patients with TPO mutations followed for up to 29 years. Twenty-two patients from six core families with congenital hypothyroidism (CH) and IOD living in the same region. All subjects underwent clinical, hormonal and imaging evaluation. The TPO gene was directly sequenced and the presence of specific mutations among family members was determined by restriction fragment length polymorphism (RFLP). All patients had congenital and persistent primary hypothyroidism. The thyroid gland was demonstrated in all subjects by technetium (99mTc) scans. A positive perchlorate discharge test (mean 87%) was indicative of IOD. Enlargement of the thyroid gland was shown in 64% of our patients, mostly with multinodular appearance, and in some with retrosternal invasion. Neurological complications were observed in 13 patients (59%). Four subjects, who carry two different TPO mutations, had sensorineural deafness. Two previously described TPO gene mutations [G1567A (G493S) and C1708T (R540X)] and one novel TPO gene mutation [C965T (S292F)] were identified. The two previously described mutations were present in 90% of the subjects. Haplotyping suggested a distant common ancestry for each of these two mutations. Three different TPO gene mutations were found to be responsible for IOD in a consanguineous Israeli population. The high rate of development of multinodular glands (MNGs) in our cohort of patients indicates the need for long-term follow-up of patients with TPO gene mutations.

Comparison of MRI findings with traditional criteria in diagnosis of Pendred syndrome

Pendred syndrome, defined as the constellation of goiter, sensori-neural hearing loss, and positive perchlorate discharge test, is the most frequent cause of congenital deafness. Newly introduced diagnostic approaches to the disease are rather expensive and complicated, therefore we evaluated the value of MRI as the sole, or adjunctive diagnostic approach, and compared it with the traditional ones. Presuming the classic triad as the gold standard, we compared MRI findings in six such defined patients with six cases having goiter, hearing loss, and normal perchlorate discharge test. Our results indicated that MRI was 83.6% sensitive and 66.7% specific in patients fulfilling all three criteria (complete), while in the ‘partial’ group the sensitivity and specificity were 66.7% and 100% respectively. In conclusion, MRI, although impressive as an adjunctive diagnostic tool, may not replace the holistic approach, and the latter may be more convenient, cheaper, and still more accurate. However in ‘partial’ cases with equivocal findings, and in relatives of the patients, MRI may be a valuable diagnostic adjunct.

Three Mutations (p.Q36H, p.G418fsX482, and g.IVS19-2A>C) in the Dual Oxidase 2 Gene Responsible for Congenital Goiter and Iodide Organification Defect

Iodide organification defects are associated with mutations in the dual oxidase 2 (DUOX2) gene and are characterized by a positive perchlorate discharge test. These mutations produce a congenital goitrous hypothyroidism, usually transmitted in an autosomal recessive mode. We studied the complete coding sequence of the human DUOX2 gene by single-strand conformational polymorphism (SSCP) analysis of DNA from 17 unrelated patients with iodide organification defects. Samples showing an aberrant pattern were directly sequenced. All mutations were validated by SSCP analysis. Finally, the effect of a splicing mutation was studied by construction of minigenes. Genomic DNA sequencing revealed 3 novel mutations [c.108G>C (p.Q36H), c.1253delG (p.G418fsX482), and g.IVS19-2A>C] and 1 previously reported mutation [c.2895-2898delGTTC (p.S965fsX994)] in 2 families with 1 (family 1) and 2 (family 2) affected members. This implies the inheritance of 2 compound heterozygous mutations, p.Q36H and p.S965fsX994 in family 1 and p.G418fsX482 and g.IVS19-2A>C in family 2. The c.1253delG mutation was associated with a c.1254C>A transversion. In vitro transcription analysis showed that exon 20 is skipped entirely when the g.IVS19-2A>C mutation is present. The wild-type glutamine residue at position 36 is strictly conserved. Two previously unknown compound heterozygous mutations in the DUOX2 gene, p.Q36H/p.S965fsX994 and p.G418fsX482/g.IVS19-2A>C, are responsible for iodide organification defects in 2 unrelated families. Identification of the molecular basis of this disorder might be helpful for understanding the pathophysiology of this congenital hypothyroidism.

Total Iodide Organification Defect: Clinical and Molecular Characterization of an Italian Family

Thyroid peroxidase (TPO) deficiency is frequently involved in total iodide organification defects (TIOD). According to the recessive mode of inheritance, mutations are found in homozygous or in compound heterozygous states. However, a single heterozygous TPO mutation is reported in a high percentage (approximately 20%) of patients with typical TIOD phenotype. In the present study, the genetic and clinical evaluation of a TIOD family is reported. The propositus is an Italian girl with congenital hypothyroidism and positive perchlorate discharge test. Two TPO frameshift mutations were documented: a C deletion at 477 in exon 5, and a GGCC duplication at 1277 in exon 8. Unaffected family members, heterozygous for one of the two TPO mutations, were also studied in order to evaluate in vivo the functional activity of a single TPO allele. They have been found to have normal thyroid morphology and function with normal perchlorate test. In conclusion, the present study reports the clinical and molecular investigations in an Italian TIOD family. The results show that the TIOD phenotype in the propositus is associated to a compound heterozygous pattern, while a single TPO mutation does not significantly affect in vivo the efficiency of iodide organification. Therefore, extensive analyses of TPO gene and 2p25 locus are needed in the frequent TIOD cases in whom conventional investigations disclosed only one mutant allele.

Molecular Analysis of thePDSGene in a Nonconsanguineous Sicilian Family with Pendred's Syndrome

Objective: The autosomal recessive Pendred's syndrome is defined by congenital sensorineural deafness, goiter, and impaired iodide organification. It is caused by mutations in the Pendred's syndrome (PDS) gene that encodes pendrin, a chloride/iodide transporter expressed in the thyroid, the inner ear, and the kidney. In this study we performed clinical and molecular analyses in three siblings from a nonconsanguineous Sicilian family who presented with the clinical features of Pendred's syndrome. Patients and Molecular Analyses: In two sisters and one brother, the clinical diagnosis of Pendred's syndrome was established based on the findings of sensorineural hearing loss and large goiters. Thyroid function tests, perchlorate discharge tests, thyroid ultrasound, and scintigraphy were performed in all affected individuals. Exons 2 to 21 of the PDS gene were amplified by polymerase chain reaction (PCR) and both strands were submitted to direct sequence analysis. Results: The clinical diagnosis of Pendred's syndrome was supported by a positive perchlorate discharge test in the three afflicted siblings. Direct sequence analysis of the PDS gene revealed that all three harbored one allele with a novel mutation 890delC leading to a frameshift mutation and premature stop codon at position 302 (FS297 > 302X). On the other allele, two of the siblings had a previously described transition 1226G > A, which results in the substitution of arginine by histidine at position 409 (R409H). In the index patient, no mutation could be identified on the other allele. In functional studies, these mutants lose the ability of pendrin to mediate iodide efflux. Conclusions: All three patients included in this study presented with the classic Pendred syndrome triad. Two siblings were compound heterozygous for mutations in the coding region of the PDS gene. The third individual could have an unidentified mutation in a regulatory or intronic region of the PDS gene, or an identical phenotype caused by distinct pathogenic mechanisms.

Molecular Analysis of the PDS Gene in a Nonconsanguineous Sicilian Family with Pendred's Syndrome

The autosomal recessive Pendred's syndrome is defined by congenital sensorineural deafness, goiter, and impaired iodide organification. It is caused by mutations in the Pendred's syndrome (PDS) gene that encodes pendrin, a chloride/iodide transporter expressed in the thyroid, the inner ear, and the kidney. In this study we performed clinical and molecular analyses in three siblings from a nonconsanguineous Sicilian family who presented with the clinical features of Pendred's syndrome. PATIENTS AND MOLECULAR ANALYSES: In two sisters and one brother, the clinical diagnosis of Pendred's syndrome was established based on the findings of sensorineural hearing loss and large goiters. Thyroid function tests, perchlorate discharge tests, thyroid ultrasound, and scintigraphy were performed in all affected individuals. Exons 2 to 21 of the PDS gene were amplified by polymerase chain reaction (PCR) and both strands were submitted to direct sequence analysis. The clinical diagnosis of Pendred's syndrome was supported by a positive perchlorate discharge test in the three afflicted siblings. Direct sequence analysis of the PDS gene revealed that all three harbored one allele with a novel mutation 890delC leading to a frameshift mutation and premature stop codon at position 302 (FS297 > 302X). On the other allele, two of the siblings had a previously described transition 1226G > A, which results in the substitution of arginine by histidine at position 409 (R409H). In the index patient, no mutation could be identified on the other allele. In functional studies, these mutants lose the ability of pendrin to mediate iodide efflux. All three patients included in this study presented with the classic Pendred syndrome triad. Two siblings were compound heterozygous for mutations in the coding region of the PDS gene. The third individual could have an unidentified mutation in a regulatory or intronic region of the PDS gene, or an identical phenotype caused by distinct pathogenic mechanisms.

Mutations in the SLC26A4 (pendrin) gene in patients with sensorineural deafness and enlarged vestibular aqueduct.

Pendred syndrome and the enlarged vestibular aqueduct (EVA) are considered phenotypic variations of the same entity due to mutations in the SLC26A4 (pendrin) gene. Pendred syndrome consists in sensorineural deafness, goiter and impaired thyroid hormone synthesis while in EVA thyroid function seems to be preserved. The aim of this study was to evaluate thyroid function and morphology and to look for mutations in the SLC26A4 gene in patients presented with EVA. Among 57 consecutive patients with sensorineural deafness 15 with EVA, as assessed by magnetic resonance imaging (MRI), were identified and studied. A complete evaluation of thyroid function including thyroid echography and perchlorate discharge test was carried out in all patients with EVA; all exons of the SLC26A4 gene were amplified from peripheral leukocytes and directly sequenced, using specific intronic primers. Out of 15 patients with EVA, goiter was present in 8 (53%), hypothyroidism in 7 (47%), increased serum thyroglobulin levels in 8 (53%) and a positive perchlorate discharge test in 10 (67%). Nine alleles of the SLC26A4 gene were mutated: 2 novel mutations (L465W and G497R) and 4 already known mutations (T410M, R409H, T505N and IVS1001+1G>A) were found. Four subjects were compound heterozygous and 1 heterozygous (G497R/wt). All patients harbouring mutations in the SLC26A4 gene had goiter and a positive perchlorate discharge test: 3 were slightly hypothyroid and 2 euthyroid. The remaining 10 patients had no mutations in the SLC26A4 gene: 4 of them were hypothyroid, 2 with goiter and positive perchlorate discharge test, 2 without goiter and with negative perchlorate discharge test. Two patients without mutations were euthyroid with positive perchlorate discharge test. Patients with mutations in the SLC26A4 gene had larger thyroid volume (p<0.002), higher serum thyroglobulin (Tg) levels (p<0.002) and greater radioiodine discharge after perchlorate (p=0.09) than patients without mutations. The results of the present study lend support to the concept that all patients with mutated SLC26A4 gene have abnormalities of thyroid function tests.

Pendred's syndrome with goiter and enlarged vestibular aqueducts diagnosed by PDS gene mutation

Pendred's syndrome (PS) is an autosomal recessive disorder characterized by goiter and congenital sensorineural hearing loss. Recent advances in molecular biology revealed the gene responsible for PS (PDS) and provided an important aid for the diagnosis of this condition. A case of PS with huge goiter and congenital hearing impairment was diagnosed by mutational analysis of the PDS gene. Physical examination and computer tomography CT revealed a diffuse swelling of the thyroid gland. Thyroid function tests were normal, and the perchlorate discharge test was negative. Audiologic examination confirmed sensorineural hearing loss, and temporal bone CT revealed bilateral enlarged vestibular aqueducts. The mutational analysis revealed that the patient was homozygous for His 723 Arg (2168A-->G) in exon 19, a missense mutation. The results of thyroid function tests in PS patients are usually normal, and the positive perchlorate discharge test has been used for the diagnosis. However, this is a nonspecific test and is not sensitive enough for PS. In our case, despite a negative perchlorate test, the patient was diagnosed by mutational analysis and received total thyroidectomy to relieve respiratory distress caused by thyroid enlargement. This is the first report of a mutation detected in the thyroid tissue and clearly shows that the mutation caused histopathologic change in that gland.

Fluctuant, progressive hearing loss associated with Menière like vertigo in three patients with the Pendred syndrome

Objective: To evaluate vestibular and long-term audiometric findings in patients with Pendred syndrome. Study design: Retrospective analysis of long-term clinical data. Setting: University hospital department. Patients: Three patients with Pendred syndrome caused by a mutation in the SLC26A4 gene. Methods: Perchlorate discharge test, mutation analysis of the SLC26A4 gene, MR imaging of temporal bones, vestibular function test (in two cases) and serial audiometry. A saturation hyperbola with onset age was fitted to the audiometric threshold-on-age data using a nonlinear regression method. The residues remaining after regression were analyzed in a correlation analysis to detect significant ipsilateral or contralateral cofluctuation. Results: All three patients had a mutation in the SLC26A4 gene and bilateral enlarged vestibular aqueduct; two of them had a positive perchlorate discharge test but in one of two siblings this test was negative. Hearing loss was significantly progressive with significant ipsilateral and contralateral cofluctuation in all evaluable cases, combined with episodes of Menière like vertigo in two cases. The episodes of vertigo are as seen in Menière disease. One case had unilateral caloric areflexia and one had bilateral vestibular hyporeflexia, proven to be progressive in a repeat examination. Conclusions: Patients with Pendred syndrome may exhibit progressive and fluctuant hearing loss with episodes of vertigo.

Pendrin, the Protein Encoded by the Pendred Syndrome Gene (PDS), Is an Apical Porter of Iodide in the Thyroid and Is Regulated by Thyroglobulin in FRTL-5 Cells

Pendred syndrome is an autosomal recessive disorder characterized by congenital deafness and thyroid goiter. The thyroid disease typically develops around puberty and is associated with a mild organification defect, characterized by an inappropriate discharge of iodide upon perchlorate stimulation (a positive perchlorate discharge test). The gene (PDS) mutated in Pendred syndrome is expressed in thyroid and encodes a 780-amino acid protein (pendrin) that has recently been shown to function as an iodide/chloride transporter. We sought to establish the location of pendrin in the thyroid and to examine the regulatory network controlling its synthesis. Using peptide-specific antibodies for immunolocalization studies, pendrin was detected in a limited subset of cells within the thyroid follicles, exclusively at the apical membrane of the follicular epithelium. Interestingly, significantly greater amounts of pendrin were encountered in thyroid tissue from patients with Graves' disease. Using a cultured rat thyroid cell line (FRTL-5), PDS expression was found to be significantly induced by low concentrations of thyroglobulin (TG), but not by TSH, sodium iodide, or insulin. This is different from the established effect of TG, more typically a potent suppressor of thyroid-specific gene expression. Together, these results suggest that pendrin is an apical porter of iodide in the thyroid and that the expression and function of both the apical and basal iodide porters are coordinately regulated by follicular TG.

Pendred syndrome: Phenotypic variability in two families carrying the samePDS missense mutation

Pendred syndrome comprises congenital sensorineural hearing loss, thyroid goiter, and positive perchlorate discharge test. Recently, this autosomal recessive disorder was shown to be caused by mutations in the PDS gene, which encodes an anion transporter called pendrin. Molecular analysis of the PDS gene was performed in two consanguineous large families from Southern Tunisia comprising a total of 23 individuals affected with profound congenital deafness; the same missense mutation, L445W, was identified in all affected individuals. A widened vestibular aqueduct was found in all patients who underwent computed tomography (CT) scan exploration of the inner ear. In contrast, goiter was present in only 11 affected individuals, who interestingly had a normal result of the perchlorate discharge test whenever performed. The present results question the sensitivity of the perchlorate test for the diagnosis of Pendred syndrome and support the use of a molecular analysis of the PDS gene in the assessment of individuals with severe to profound congenital hearing loss associated with inner ear morphological anomaly even in the absence of a thyroid goiter.

A novel mutation in the TPO gene in goitrous hypothyroid patients with iodide organification defect.

To screen and subsequently sequence the TPO gene for mutations in patients with congenital goitre, hypothyroidism and evidence for an organification defect (positive perchlorate discharge test). We have studied seven hypothyroid and congenitally goitrous patients from three unrelated families. We have measured serum thyroid hormone levels, 131I uptake, serum TSH and serum Tg concentrations. Denaturing gradient gel electrophoresis (DGGE) of PCR amplified genomic DNA was used to screen for mutations in the TPO gene. DGGE identified the presence of two frameshift mutations: a GGCC duplication in exon 8 (homozygous in one family and heterozygous in the other family) and a heterozygous insertion of a single nucleotide (C) at position 2505-2511 in exon 14. In addition, we have detected an alteration in exon 11, not yet described in the literature, derived from a single nucleotide substitution of a C to G at position 2008, altering the well-conserved amino acid domain among the peroxidases superfamily. This mutation in exon 11 was present in two families that showed heterozygous mutation for exon 8 or for exon 14. These results could support the hypothesis for a putative compound heterozygosity pattern in the affected patients. The altered phenotype (goitre and hypothyroidism since birth) seems justifiable in view of the possible inactivating character of this novel mutation in exon 11.

Clinical, Pathological, and Molecular Studies of Two Families with Iodide Organification Defect.

Two unrelated families (CA and NA) in which an iodide organification defect (lOD) was present in two siblings of each family were studied. These patients had congenital goiters with hypothyroidism and a positive perchlorate discharge test. Examination of the thyroid tissue revealed no thyroid peroxidase (TPO) activity. Histologic findings were consistent with a microfollicular pattern of hyperplasia. Moderate cellular atypia was present, characterized by nuclear pleomorphism and hyperchromatism. Full length thyroglobulin was purified by gel filtration, but was not iodinated. Immunohistochemical studies using a polyclonal anti-human thyroid peroxidase (hTPO) antibody confirmed the presence of immunoreactive TPO protein in the thyroid tissues. Samples of normal and affected individuals were studied with respect to the presence of various fragments using TPO probes of varying sizes. The two affected siblings from family CA were homozygous for fragments 3.9, 4.6, and 7.0 kb (8g111) and 2.3 and 2.9 kb (Ta ql), whereas the parents were heterozygous. In the other family (NA), the Bg/ll digestion and TPO-31 hybridization revealed an interesting and informative polymorphism. The parents showed two different polymorphic patterns: the father had a 5.0/4.6 kb pattern and the mother a 4.7/4.5 kb pattern. However, the two affected siblings showed the same heterozygotic allelic pattern at 4.5/4.6 kb. The restriction fragment length polymorphism detected in these two families suggests an association between the TPO gene and an lOD. Results suggest that in these dyshormonogenetic tissues an altered TPO protein molecule is being synthesized, without detectable in vitro activity, but visible by immunostaining techniques in the goitrous tissue. Mutations in the TPC gene sequence are most likely associated with these changes.

Transient iodine organification defect in infants with ectopic thyroid glands.

Thyroid gland ectopy is the most common cause in infants with congenital hypothyroidism (CH). Its association with iodine organification defect, as suggested by positive perchlorate discharge test (PDT) has been reported. However, whether such an association represents a true or transient defect has not yet been determined. This finding has an important clinical, epidemiological, and genetic implications. To determine the natural history of iodine organification defect in patients with CH caused by thyroid ectopy detected by neonatal screening. Prospective longitudinal study. King Khalid University Hospital, Riyadh, Saudi Arabia. PDT was performed, at the time of diagnosis and follow-up, in infants who showed an enlarged ectopic thyroid gland with a Tc-99m pertechnetate uptake of 2% or more. Of 115 neonates with ectopic thyroid glands, 19 showed an enlarged gland with Tc-99m uptake ranging from 2 to 3.2%. Perchlorate discharge test was performed in 13 of these and was consistent with iodine organification defect in nine. Repeated PDT in seven patients showed normal values. The results of the authors' study indicate the transient nature of the iodine organification defect and suggest that a delay in the developmental of synthetic mechanisms occur in the dysgenetic glands.