Molecular analysis of the Pendred's syndrome gene and magnetic resonance imaging studies of the inner ear are essential for the diagnosis of true Pendred's syndrome

Clinical use of thyroglobulin: not only thyroid cancer

Thyroglobulin (TG) is a dimeric glycoprotein produced exclusively by mature thyroid tissue and stored within the follicular lumen. It is essential for the organification of iodine and the production of thyroid hormones. The concentration of TG in the bloodstream varies between individuals and depends on factors such as thyroid mass, stimulation of the gland by thyrotropin or autoantibodies, and tissue destruction. TG is essential to monitor patients with differentiated thyroid cancer; however, its use is not limited only to this clinical entity. Measurement of circulating TG can provide better insight into numerous clinical scenarios, such as destructive thyroiditis, presence of ectopic thyroid tissue, thyroid trauma, factitious thyrotoxicosis, or iodine nutrition. Lately, TG has found its new clinical use in immune checkpoint-related thyroid dysfunction. TG measurement should be performed carefully in patients with antithyroglobulin antibodies due to possible laboratory interferences. In this review, we offer a summary of current knowledge about the clinical use of TG and the implications it brings to daily practice.

Neonatal Dyshormonogenetic Goiter with Hypothyroidism Associated with Novel Mutations in Thyroglobulin and SLC26A4 Gene

Congenital goiter is an uncommon cause of neck swelling and it can be associated with hypothyroidism. We discuss a case of primary hypothyroidism with goiter presenting at birth. Ultrasound showed the enlargement of the gland and thyroid function tests detected marked hypothyroidism. Genetic analysis via next generation sequencing (NGS) was performed finding two mutations associated with thyroid dyshormonogenesis: c.7813 C > T, homozygous in the exon 45 of the thyroglobulin gene (TG) and c.1682 G > A heterozygous in exon 15 of the SLC26A4 gene (pendrin). Sanger sequencing of parents' DNA samples revealed that the first mutation (c.7813 C > T) was inherited from both of them, while the second one (c.1682 G > A) was inherited from the mother. Hormone replacement therapy was started, following which a gradual decrease in the size of the goiter was seen with the normalization of hormonal levels. Normal infant growth status and neurological development were recorded during follow-up. Neonatal dyshormonogenetic goiter with hypothyroidism may represent an unusual cause of neonatal neck mass. Early identification and hormone replacement therapy are crucial for a better neurodevelopmental outcome. Genetic analysis is mandatory in order to reach a specific diagnosis and to elucidate new patterns of thyroid disorder.

Pendred syndrome with hyperthyroidism

Objectives: Pendred syndrome is an autosomal recessive disorder characterized by the combination of sensorineural deafness and goiter and is caused by biallelic mutations in the SLC26A4/PDS gene. Thyroid function is generally reported as euthyroid or hypothyroid in this condition. We present a case of Pendred syndrome with hyperthyroidism.

Patient: An 83-year-old woman with congenital deaf–mutism presented with complaints of nausea. She developed a large goiter and had hearing impairment. Her hearing level was 105 dB in both ears. She presented with hyperthyroidism and was treated with thiamazole.

Results: She had a homozygous mutation in c.1579A>C:p.T527P of the SLC26A4 gene, confirming a diagnosis of Pendred syndrome.

Conclusion: Pendred syndrome may develop into hyperthyroidism if the size of the goiter increases. Moreover, a homozygous mutation in c.1579A>C:p.T527P of the SLC26A4 gene, which was previously reported to be associated with nonsyndromic hearing loss with enlarged vestibular aqueduct, may also cause Pendred syndrome.

Segmental Maternal UPD of Chromosome 7q in a Patient With Pendred and Silver Russell Syndromes-Like Features

Pendred syndrome (PS) is an autosomal recessive disorder due to mutations in the SLC26A4 gene (chr7q22. 3) and characterized by sensorineural hearing loss and variable thyroid phenotype. Silver-Russell syndrome (SRS) is a heterogeneous imprinting disorder including severe intrauterine and postnatal growth retardation, and dysmorphic features. Maternal uniparental disomy of either the whole chromosome 7 (upd(7)mat) or 7q (upd(7q)mat) is one of the multiple mechanisms impacting the expression of imprinted genes in SRS, and is associated with milder clinical features. Here, we report genetic and clinical characterization of a female child with PS, postnatal growth retardation, and minor dysmorphic features. A gross homozygous deletion of SLC26A4 exons 17-20 was suspected by Sanger sequencing and then confirmed by array-CGH. Moreover, an insertion of about 1 kb of the CCDC126 gene (7p15.3), which does not appear to be clinically relevant, was detected. The possible occurrence of a balanced rearrangement between 7p and 7q was excluded. The absence of the deletion in the father led to the investigation of upd, and microsatellite segregation analysis revealed a segmental 7q (upd(7q)mat), leading to SLC26A4 homozygosity and responsible for both PS and SRS-like traits. The proband matched 3 out of 6 major SRS criteria. In conclusion, this is the first report of uniparental isodisomy encompassing almost the whole long arm of chromosome 7 resulting in PS and SRS-like features. Whereas, the inner ear phenotype of PS is typical, the clinical features suggestive of SRS might have been overlooked.

Syndromic Hearing Loss: A Brief Review of Common Presentations and Genetics

Congenital hearing loss is one of the most common birth defects worldwide, with around 1 in 500 people experiencing some form of severe hearing loss. While over 400 different syndromes involving hearing loss have been described, it is important to be familiar with a wide range of syndromes involving hearing loss so an early diagnosis can be made and early intervention can be pursued to maximize functional hearing and speech-language development in the setting of verbal communication. This review aims to describe the presentation and genetics for some of the most frequently occurring syndromes involving hearing loss, including neurofibromatosis type 2, branchio-oto-renal syndrome, Treacher Collins syndrome, Stickler syndrome, Waardenburg syndrome, Pendred syndrome, Jervell and Lange-Nielsen syndrome, Usher syndromes, Refsum disease, Alport syndrome, MELAS, and MERRF.

Exome sequencing identifies SLC26A4, GJB2, SCARB2 and DUOX2 mutations in 2 siblings with Pendred syndrome in a Malaysian family

BACKGROUND

Pendred syndrome (PDS, MIM #274600) is an autosomal recessive disorder characterized by congenital sensorineural hearing loss and goiter. In this study, we describing the possible PDS causal mutations in a Malaysian family with 2 daughters diagnosed with bilateral hearing loss and hypothyroidism.

METHODS AND RESULTS

Whole exome sequencing was performed on 2 sisters with PDS and their unaffected parents. Our results showed that both sisters inherited monoallelic mutations in the 2 known PDS genes, SLC26A4 (ENST00000265715:c.1343C > T, p.Ser448Leu) and GJB2 (ENST00000382844:c.368C > A, p.Thr123Asn) from their father, as well as another deafness-related gene, SCARB2 (ENST00000264896:c.914C > T, p.Thr305Met) from their mother. We postulated that these three heterozygous mutations in combination may be causative to deafness, and warrants further investigation. Furthermore, we also identified a compound heterozygosity involving the DUOX2 gene (ENST00000603300:c.1588A > T:p.Lys530* and c.3329G > A:p.Arg1110Gln) in both sisters which are inherited from both parents and may be correlated with early onset of goiter. All the candidate mutations were predicted deleterious by in silico tools.

CONCLUSIONS

In summary, we proposed that PDS in this family could be a polygenic disorder which possibly arises from a combination of heterozygous mutations in SLC26A4, GJB2 and SCARB2 which associated with deafness, as well as compound heterozygous DUOX2 mutations which associated with thyroid dysfunction.

Molecular epidemiology and functional assessment of novel allelic variants of SLC26A4 in non-syndromic hearing loss patients with enlarged vestibular aqueduct in China

Background

Mutations in SLC26A4, which encodes pendrin, are a common cause of deafness. SLC26A4 mutations are responsible for Pendred syndrome and non-syndromic enlarged vestibular aqueduct (EVA). The mutation spectrum of SLC26A4 varies widely among ethnic groups. To investigate the incidence of EVA in Chinese population and to provide appropriate genetic testing and counseling to patients with SLC26A4 variants, we conducted a large-scale molecular epidemiological survey of SLC26A4.

Methods

A total of 2352 unrelated non-syndromic hearing loss patients from 27 different regions of China were included. Hot spot regions of SLC26A4, exons 8, 10 and 19 were sequenced. For patients with one allelic variant in the hot spot regions, the other exons were sequenced one by one until two mutant alleles had been identified. Patients with SLC26A4 variants were then examined by temporal bone computed tomography scan for radiological diagnosis of EVA. Ten SLC26A4 variants were cloned for functional study. Confocal microscopy and radioisotope techniques were used to examine the membrane expression of pendrin and transporter function.

Results

Of the 86 types of variants found, 47 have never been reported. The ratio of EVA in the Chinese deaf population was at least 11%, and that in patients of Han ethnicity reached at least 13%. The mutational spectrum and mutation detection rate of SLC26A4 are distinct among both ethnicities and regions of Mainland China. Most of the variants caused retention of pendrin in the intracellular region. All the mutant pendrins showed significantly reduced transport capability.

Conclusion

An overall description of the molecular epidemiological findings of SLC26A4 in China is provided. The functional assessment procedure can be applied to identification of pathogenicity of variants. These findings are valuable for genetic diagnosis, genetic counseling, prenatal testing and pre-implantation diagnosis in EVA families.

Identification of allelic variants of pendrin (SLC26A4) with loss and gain of function

BACKGROUND

Pendrin is a multifunctional anion transporter that exchanges chloride and iodide in the thyroid, as well as chloride and bicarbonate in the inner ear, kidney and airways. Loss or reduction in the function of pendrin results in both syndromic (Pendred syndrome) and non-syndromic (non-syndromic enlarged vestibular aqueduct (ns-EVA)) hearing loss. Factors inducing an up-regulation of pendrin in the kidney and the lung may have an impact on the pathogenesis of hypertension, chronic obstructive pulmonary disease (COPD) and asthma. Here we characterize the ion transport activity of wild-type (WT) pendrin and seven of its allelic variants selected among those reported in the single nucleotide polymorphisms data base (dbSNPs), some of which were previously identified in a cohort of individuals with normal hearing or deaf patients belonging to the Spanish population.

METHODS

WT and mutated pendrin allelic variants were functionally characterized in a heterologous over-expression system by means of fluorometric methods evaluating the I(-)/Cl(-) and Cl(-)/OH(-) exchange and an assay evaluating the efflux of radiolabeled iodide.

RESULTS

The transport activity of pendrin P70L, P301L and F667C is completely abolished; pendrin V609G and D687Y allelic variants are functionally impaired but retain significant transport. Pendrin F354S activity is indistinguishable from WT, while pendrin V88I and G740S exhibit a gain of function.

CONCLUSION

Amino acid substitutions involving a proline always result in a severe loss of function of pendrin. Two hyperfunctional allelic variants (V88I, G740S) have been identified, and they may have a contributing role in the pathogenesis of hypertension, COPD and asthma.

Functional characterization of pendrin mutations found in the Israeli and Palestinian populations

BACKGROUND

Pendrin is a transport protein exchanging chloride for other anions, such as iodide in the thyroid gland or bicarbonate in the inner ear. Mutations in the SLC26A4 gene encoding for pendrin are responsible for both syndromic (Pendred syndrome) and non-syndromic (non-syndromic enlarged vestibular aqueduct, EVA) hearing loss. Besides clinical and radiological assessments, molecular and functional studies are essential for the correct diagnosis of Pendred syndrome and non-syndromic EVA. While a broad spectrum of mutations found in the Caucasian population has been functionally characterized, little is known about mutations specifically occurring in the populations of the Middle East. Here we show the characterization of the ion transport activity of three pendrin mutations previously found in deaf patients with EVA in the Israeli Jewish and Palestinian Arab populations, i.e. V239D, G334V X335 and I487Y FSX39.

METHODS

Wild type and mutated pendrin allelic variants were functionally characterized in a heterologous over-expression system. The Cl(-)/I(-) and Cl(-)/OH(-) exchange activities were assessed by fluorometric methods suitable for measuring iodide fluxes and the intracellular pH.

RESULTS

Both the Cl(-)/I(-) and the Cl(-)/OH(-) exchange activities of pendrin V239D, G334V X335 and I487Y FSX39 were significantly reduced with respect to the wild type, with V239D displaying a residual iodide transport.

CONCLUSION

Functional assays confirmed the diagnosis of non-syndromic EVA due to SLC26A4 mutations performed by radiological and molecular tests in deaf patients belonging to the Israeli Jewish and Palestinian Arab populations. The new finding that the V239D mutation displays residual function suggests that the symptoms caused by this mutation could be ameliorated by a pendrin 'activator', if available.

Absence of primary hypothyroidism and goiter in Slc26a4 (-/-) mice fed on a low iodine diet

BACKGROUND

Mutations in the SLC26A4 gene, coding for the anion transporter pendrin, are responsible for Pendred syndrome, characterized by congenital sensorineural deafness and dyshormonogenic goiter. The physiological role of pendrin in the thyroid is still unclear and the lack of a thyroid phenotype in some patients with SLC26A4 mutations and in Slc26a4 (-/-) mice indicate the existence of environmental or individual modifiers able to compensate for pendrin inactivation in the thyroid. Since pendrin can transport iodide in vitro, variations in iodide supply have been claimed to account for the thyroid phenotype associated with pendrin defects.

AIM

The Slc26a4 (-/-) mouse model was used to test the hypothesis that iodide supply may influence the penetrance and expressivity of SLC26A4 mutations.

MATERIALS AND METHODS

Slc26a4 (-/-) and (+/+) mice were fed up to 6 months on a standard or low iodine diet and were evaluated for thyroid structural abnormalities or biochemical hypothyroidism.

RESULTS

A 27-fold iodide restriction induced similar modifications in thyroid histology, but no differences in thyroid size, T4 or TSH levels were observed between between Slc26a4 (-/-) and (+/+) mice, either in standard conditions and during iodine restriction.

CONCLUSIONS

Iodide restriction is not able to induce a thyroid phenotype in Slc26a4 (-/-) mice. These experimental data, together with those coming from a review of familial Pendred cases leaving in regions either with low or sufficient iodide supply, support the idea that the expression of thyroid phenotype in Pendred syndrome is more powerfully influenced by individual factors than by dietary iodide.

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.

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.

Minireview: The sodium-iodide symporter NIS and pendrin in iodide homeostasis of the thyroid

Thyroid hormones are essential for normal development and metabolism. Thyroid hormone biosynthesis requires iodide uptake into the thyrocytes and efflux into the follicular lumen, where it is organified on selected tyrosyls of thyroglobulin. Uptake of iodide into the thyrocytes is mediated by an intrinsic membrane glycoprotein, the sodium-iodide symporter (NIS), which actively cotransports two sodium cations per each iodide anion. NIS-mediated transport of iodide is driven by the electrochemical sodium gradient generated by the Na(+)/K(+)-ATPase. NIS is expressed in the thyroid, the salivary glands, gastric mucosa, and the lactating mammary gland. TSH and iodide regulate iodide accumulation by modulating NIS activity via transcriptional and posttranscriptional mechanisms. Biallelic mutations in the NIS gene lead to a congenital iodide transport defect, an autosomal recessive condition characterized by hypothyroidism, goiter, low thyroid iodide uptake, and a low saliva/plasma iodide ratio. Pendrin is an anion transporter that is predominantly expressed in the inner ear, the thyroid, and the kidney. Biallelic mutations in the SLC26A4 gene lead to Pendred syndrome, an autosomal recessive disorder characterized by sensorineural deafness, goiter, and impaired iodide organification. In thyroid follicular cells, pendrin is expressed at the apical membrane. Functional in vitro data and the impaired iodide organification observed in patients with Pendred syndrome support a role of pendrin as an apical iodide transporter.

[Large endolymphatic duct and sac syndrome (LEDS) : part I: analysis of imaging findings]

OBJECTIVE

Large endolymphatic duct and sac (LEDS) syndrome is the most common radiologically detectable form of inner ear malformation (IEM) associated with sensorineural hearing loss (SNHL). Nevertheless, it is relatively unknown in the German-speaking countries.

METHODS

Among all patients referred from ear, nose, and throat specialists to the radiology department with clinically suspected IEM between 1994 and 2003, we identified the cases of LEDS. The retrospective study included clinical records, high-resolution computed tomography, and magnetic resonance imaging.

RESULTS

Of 169 patients, 17 (median age 12 years; 12 females) showed LEDS. A total of 28 ears were affected. Ten patients (6%; 15 ears) had isolated LEDS, while seven patients showed additional IEM (4%; 13 ears). The most frequent of these was dysplastic vestibule (13/13 ears), followed by Mondini deformity (10/13 ears) and dilated semicircular canals (7/13 ears). Three of 13 ears revealed severe IEM of the cochlea, vestibule, and semicircular canals. No correlation could be demonstrated between the severity of morphological changes and the degree of SNHL.

CONCLUSION

LEDS may be an underestimated cause of SNHL. Imaging is necessary for a confident diagnosis.

Pendred syndrome in two Galician families: insights into clinical phenotypes through cellular, genetic, and molecular studies

CONTEXT

We studied two families from Galicia (northwest Spain) with Pendred syndrome (PS) and unusual thyroid phenotypes. In family A, the proposita had a large goiter and hypothyroxinemia but normal TSH and free T3 (FT3). In family B, some affected members showed deafness but not goiter.

OBJECTIVE

Our objective was to identify the mutations causing PS and molecular mechanisms underlying the thyroid phenotypes.

INTERVENTIONS

Interventions included extraction of DNA and of thyroid tissue.

PATIENTS

Propositi and 10 members of the two families participated in the study.

MAIN OUTCOME MEASURES

Main outcome measures included SLC26A4 gene analysis, deiodinase activities in thyroid tissue, and c.416-1G-->A effects on SLC26A4 splicing. In addition, a primary PS thyrocyte culture, T-PS2, was obtained from propositus B and compared with another culture of normal human thyrocytes, NT, by Western blotting, confocal microscopy, and iodine uptake kinetics.

RESULTS

Proposita A was heterozygous for c.578C-->T and c.279delT, presented with goiter, and had normal TSH and FT3 but low FT4 attributable to high type 1 and type 2 iodothyronine deiodinase activities in the goiter. Propositus B bore c.279delT and a novel mutation c.416-1G-->A; some deaf relatives were homozygous for c.416-1G-->A but did not present goiter. The c.279delT mutation was associated with identical haplotype in the two families. T-PS2 showed truncated pendrin retained intracellularly and high iodine uptake with low efflux leading to iodine retention.

CONCLUSIONS

c.279delT is a founder mutation in Galicia. Proposita A adapted to poor organification by increasing deiodinase activities in the goiter, avoiding hypothyroidism. Lack of goiter in subjects homozygous for c.416-1G-->A was due to incomplete penetrance allowing synthesis of some wild-type pendrin. Intracellular iodine retention, as seen in T-PS2, could play a role in thyroid alterations in PS.

Loss of cochlear HCO3- secretion causes deafness via endolymphatic acidification and inhibition of Ca2+ reabsorption in a Pendred syndrome mouse model

Pendred syndrome, characterized by childhood deafness and postpuberty goiter, is caused by mutations of SLC26A4, which codes for the anion exchanger pendrin. The goal of the present study was to determine how loss of pendrin leads to hair cell degeneration and deafness. We evaluated pendrin function by ratiometric microfluorometry, hearing by auditory brain stem recordings, and expression of K(+) and Ca(2+) channels by confocal immunohistochemistry. Cochlear pH and Ca(2+) concentrations and endocochlear potential (EP) were measured with double-barreled ion-selective microelectrodes. Pendrin in the cochlea was characterized as a formate-permeable and DIDS-sensitive anion exchanger that is likely to mediate HCO(3)(-) secretion into endolymph. Hence endolymph in Slc26a4(+/-) mice was more alkaline than perilymph, and the loss of pendrin in Slc26a4(-/-) mice led to an acidification of endolymph. The stria vascularis of Slc26a4(-/-) mice expressed the K(+) channel Kcnj10 and generated a small endocochlear potential before the normal onset of hearing at postnatal day 12. This small potential and the expression of Kcnj10 were lost during further development, and Slc26a4(-/-) mice did not acquire hearing. Endolymphatic acidification may be responsible for inhibition of Ca(2+) reabsorption from endolymph via the acid-sensitive epithelial Ca(2+) channels Trpv5 and Trpv6. Hence the endolymphatic Ca(2+) concentration was found elevated in Slc26a4(-/-) mice. This elevation may inhibit sensory transduction necessary for hearing and promote the degeneration of the sensory hair cells. Degeneration of the hair cells closes a window of opportunity to restore the normal development of hearing in Slc26a4(-/-) mice and possibly human patients suffering from Pendred syndrome.

The H723R mutation in the PDS/SLC26A4 gene is associated with typical Pendred syndrome in Korean patients

Inherited as an autosomal recessive trait, Pendred syndrome is a disease that shows congenital sensorineural hearing loss and goiter, with a positive finding in the perchlorate discharge test. Pendred syndrome results from various mutations in the PDS/SLC26A4 gene that cause production of an abnormal pendrin protein. More than 90 mutations in the PDS/SLC26A4 gene have been reported throughout the world. A recent study of 26 Korean patients with a relatively high frequency (65%) of a mutated PDS/SLC26A4 gene exhibited nonsyndromic deafness and an enlarged vestibular aqueduct. We report two patients with characteristics of typical Pendred syndrome, a 26-yr-old female and a 61-yr-old male, who were both homozygous for a previously reported missense mutation, H723R (Histidine 723Arginine) in the PDS/SLC26A4 gene.