CONICET | Buscador de Institutos y Recursos Humanos

Background: ITD is an autosomal recessive disorder whose hallmark is the inability of the thyroid to actively accumulate iodide. ITD is an uncommon cause of dyshormonogenetic congenital hypothyroidism that results from inactivating mutations in the NIS gene (1). Clinical manifestations include low to absent thyroid and salivary iodide uptake and, if untreated, variable degrees of hypothyroidism, goiter, and even mental retardation. Objective: To determine if a pediatric patient with clinical manifestations of ITD bears a mutation in the NIS gene, and if so, to ascertain the effects of the mutation on the biogenesis and activity of NIS. Methods: The genomic DNA encoding NIS was sequenced, and in vitro functional studies of a newly identified NIS mutation were performed. Results: The patient has the compound heterozygous mutation R124H/V270E. The R124H NIS mutant has been previously identified as a cause of ITD (2,3). Here we show that the newly identified V270E NIS mutation causes a substantial decrease in I- uptake when expressed in COS-7 cells. Flow cytometry and immunofluorescence analyses revealed a severe impairment in V270E NIS targeting to the plasma membrane. Strikingly, membrane vesicles from V270E NIS-expressing cells transport I- to a similar extent to vesicles from wild-type NIS-expressing cells, indicating that, although trafficking of V270E NIS to the cell surface is impaired, the protein itself is highly functional. Replacement of V270 with Asp or Gln resulted in intracellular retention. In contrast, V270Q NIS is targeted to the cell surface and active. Conclusions: We describe a novel mutation in the NIS gene in a patient with congenital hypothyroidism and a clinical ITD phenotype. The investigation of the molecular mechanism responsible for impaired NIS activity revealed that the V270E substitution reduces NIS targeting to the plasma membrane, thus causing a decrease in I- uptake even though V270E NIS is intrinsically active.