Pendred syndrome is an autosomal recessive disorder characterized by sensorineural hearing loss, with malformations of the inner ear, ranging from enlarged vestibular aqueduct (EVA) to Mondini malformation, and deficient iodide organification in the thyroid gland. Nonsyndromic EVA (ns-EVA) is a separate type of sensorineural hearing loss showing normal thyroid function. Both Pendred syndrome and ns-EVA seem to be linked to the malfunction of pendrin (SLC26A4), a membrane transporter able to exchange anions between the cytosol and extracellular fluid. In the past, the pathogenicity of SLC26A4 missense mutations were assumed if the mutations fulfilled two criteria: low incidence of the mutation in the control population and substitution of evolutionary conserved amino acids. Here we show that these criteria are insufficient to make meaningful predictions about the effect of these SLC26A4 variants on the pendrin-induced ion transport. Furthermore, we functionally characterized 10 missense mutations within the SLC26A4 ORF, and consistently found that on the protein level, an addition or omission of a proline or a charged amino acid in the SLC26A4 sequence is detrimental to its function. These types of changes may be adequate for predicting SLC26A4 functionality in the absence of direct functional tests.ion transport physiology ͉ genotype-phenotype correlation P endred syndrome (PS) (OMIM#274600) (1) is an autosomal recessive disorder characterized by sensorineural hearing loss (SNHL) and malformations of the inner ear, ranging from enlarged vestibular aqueduct (EVA) (2) to Mondini malformation (3), combined with deficient iodide organification in the thyroid gland, as demonstrated by the positive perchlorate discharge test in affected individuals (4-7). Another form of SNHL associated with EVA, however, showing normal thyroid function, is called nonsyndromic EVA (ns-EVA) (OMIM#600791). The clinical features of PS are the consequence of impaired pendrin function (1), a protein encoded by the SLC26A4 gene (NM 000441). It is a member of the multifunctional anion transporter family SLC26, which mediates the exchange of anions including Cl Ϫ , HCO 3 Ϫ , OH Ϫ , I Ϫ , or formate (8). Pendrin seems to be responsible for the efflux of iodide in thyrocytes (9-11), and for mediating Cl Ϫ /HCO 3 Ϫ exchange in the kidney cortex (12) and inner ear. In the latter, pendrin is involved in the conditioning of endolymphatic fluid, presumably because of HCO 3 Ϫ secretion (13), thereby modifying inner ear acid-base homeostasis. A variable feature of PS is the development of goitre (apparent in only about 50% of the affected individuals). At the thyroid level, the role of pendrin is not conclusive. The transporter could act as an iodide transporter at the apical membrane of thyroid cells and impaired function could therefore lead to the iodide organification defect observed in PS patients (10,11,(14)(15)(16). PS seems to be linked to bi-allelic mutations of the SLC26A4 genes. ns-EVA is genetically more heterogeneous relative to PS, and a...

Calcium oxalate stone formation occurs under pathological conditions and accounts for more than 80% of all types of kidney stones. In the current study, we show for the first time that calcium oxalate stones are formed in the mouse inner ear of a genetic model for hearing loss and vestibular dysfunction in humans. The vestibular system within the inner ear is dependent on extracellular tiny calcium carbonate minerals for proper function. Thousands of these biominerals, known as otoconia, are associated with the utricle and saccule sensory maculae and are vital for mechanical stimulation of the sensory hair cells. We show that a missense mutation within the Slc26a4 gene abolishes the transport activity of its encoded protein, pendrin. As a consequence, dramatic changes in mineral composition, size, and shape occur within the utricle and saccule in a differential manner. Although abnormal giant carbonate minerals reside in the utricle at all ages, in the saccule, a gradual change in mineral composition leads to a formation of calcium oxalate in adult mice. By combining imaging and spectroscopy tools, we determined the profile of mineral composition and morphology at different time points. We propose a novel mechanism for the accumulation and aggregation of oxalate crystals in the inner ear.Biomineralization processes in the human body normally occur in a variety of different tissues, including bones, teeth, and otoconia within the vestibular system of the inner ear. The vestibular system is comprised of five sensory organs. Three cristae connected to semicircular canals are sensitive for angular movement, and the saccule and utricle are sensitive for linear acceleration and gravity. Otoconia are small highly dense calcitic minerals that associate exclusively with the saccule and utricle. Thousands of otoconia, partially embedded in a gelatinous matrix, are supported on the sensory epithelium and serve as an inertial mass that is critical for mechanical stimulation (1, 2) Movement of the otoconial layer through action of gravitational or inertial forces activate the underlying mechanosensory hair cells to generate action potentials that are transmitted to the brain.The biomineralization process, such as in otoconia formation, involves organic and inorganic components and results in biominerals that differ significantly in morphology and mechanical properties from similar synthetic or geological minerals (3, 4). Otoconia formation occurs outside the cells and therefore depends on secretion of the required assembly components into the endolymphatic spaces (5). Otoconia seeding in mice begins as early as embryonic day (E)14.5 4 and initiates extensive mineral growth, with the highest rate of calcification at E15-16 (6). By postnatal day (P)7, otoconia achieve their final size and are maintained at progressive ages with a low rate of calcium turnover (7). The main inorganic fraction of otoconia in birds and mammals is calcite (CaCO 3 ), a polymorph of calcium carbonate (2,8). The organic fraction of otoconia contains s...

Signaling through the interleukin-4/interleukin-13 (IL-4/IL-13) receptor complex is a crucial mechanism in the development of bronchial asthma and chronic obstructive pulmonary disease (COPD). In bronchial epithelial cells, this signaling pathway leads to changes in the expression levels of several genes that are possibly involved in protection against and/or pathogenesis of these diseases. The expression of pendrin (SLC26A4), a candidate for the latter category, is upregulated by IL-4/IL-13 and leads to overproduction of mucus and increased viscosity of the airway surface liquid (ASL). Therefore, elucidating the transcriptional regulation of pendrin could aid in the development of new pharmacological leads for asthma and/or COPD therapy. Here we show that IL-4/IL-13 significantly increased human pendrin promoter activity in HEK-Blue cells but not in STAT6-deficient HEK293 Phoenix cells; that mutation of the STAT6 binding site (N(4) GAS motif) rendered the promoter insensitive to IL-4/IL-13; and that addition of the N(4) GAS motif to an IL-4/IL-13-unresponsive sequence of the human pendrin promoter conferred sensitivity to both ILs.

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Pendred syndrome (PS) is the most frequent form of genetically related syndromic hearing loss, and is associated with mutations of pendrin, encoded by the SLC26A4 gene. This protein localizes to the cellular membrane and permits the exchange of anions between the cytosol and extracellular space. In the inner ear, pendrin conditions the endolymph, allowing for the proper function of sensory cells. Understanding the relationship between the genotype and phenotype of pendrin mutations would aid clinicians to better serve PS patients-however, little is known. Here, we summarize the available data concerning SLC26A4 mutations and how they relate to transporter function. The main findings suggest that all the truncation mutations tested annihilate pendrin function, and that the addition or omission of proline, or the addition or omission of charged amino acids in the sequence of SLC26A4 result in a substantial to dramatic reduction in pendrin function.