IDENTIFICATION OF NOVEL PATHOGENIC VARIANTS IN THE NA+/I- SYMPORTER (NIS)-CODING SLC5A5 GENE IN PEDIATRIC PATIENTS WITH DYSHORMONOGENIC CONGENITAL HYPOTHYROIDISM

CE BERNAL BARQUERO; V PEYRET; ANA CHIESA; M MARTÍN; PATRICIA PAPENDIECK; R GEYSELS; PAULA ALEJANDRA SCAGLIA; JP NICOLA

Washington

Congreso; 88th Annual Meeting of the American Thyroid Association; 2018

American Thyroid Association

Dyshormonogenic congenital hypothyroidism is caused by loss-offunctionmutations in genes required for normal thyroid hormonogenesis.Particularly, mutations in the Na+/I- symporter (NIS)-codingSLC5A5 gene cause an uncommon autosomal recessive disorderknown as I- transport defect (ITD), as a consequence of impairedI- accumulation in the thyroid follicular cell. Genomic DNA wasisolated from hole blood and the entire exonic nucleotide sequenceencoding the SLC5A5 gene was studied using Sanger sequencing.Genetic testing was approved by the institutional review board atHospital de Nin?os Dr. Ricardo Gutie´rrez. In silico computational andin vitro functional studies of newly identified NIS mutants wereperformed. Three unrelated female pediatric patients were diagnosedby neonatal screening with severe dyshormonogenic congenital hypothyroidism.ITD was suspected on the basis of non-detectableradioiodide accumulation in a normally located, non-goitrous thyroidgland, as well as in salivary glands.SLC5A5 gene analysis revealed six non-synonymous compoundheterozygous variants (p.Q136L/p.D369V, p.D331N/p.S547R, andp.G543K/p.L562M) in association with an ITD phenotype. Notably,none of them were reported in the Exome Aggregation Consortiumdatabase.The pathologic significance of all NIS mutants was investigated insilico using prediction softwares (i.e. SIFT, Polyphen-2, and MutationTaster).Prediction programs indicated that all NIS mutants mightbe disease associated.Functional studies in vitro demonstrated that the NIS mutantsp.D369V, p.S547R, and P.G543K were associated with nondetectableI- accumulation when transiently transfected into HEK-293T cells, which do not express NIS endogenously. The NISmutants p.Q136L, p.D331N, and L562M have not been tested yet.Moreover, flow cytometry, immunofluorescence and immunoblotanalysis revealed that these mutant proteins are completely retainedin the endoplasmic reticulum and, therefore do not reach the plasmamembrane. Although the mechanism by which these mutants impairNIS transport to the plasma membrane remains unknown, here weprovide a brief characterization of novel molecular events leading todefective I- accumulation in the thyroid follicular cell.