Identification and funcional characterization of a novel mutation in the Na+/I- symporter 5�f untranslated region in a patient with congenital hypothyroidism

NICOLA JP; SOBRERO DE MARTINELLI GM; SERRANO-NASCIMENTO C; NAZAR M; GOULART-SILVA F; MARTÍN SE; SILVANO L; TESTA G; NUNEZ MT; MASINI - REPISO AM; MUÑOZ L; MIRAS MB

Costa do Sauípe

Congreso; XXI Reunion Anual de la Sociedad Latino Americana de Endocrinología Pediátrica (SLEP); 2010

Sociedad Latino Americana de Endocrinología Pediátrica (SLEP)

Iodide transport defect (ITD) is an autosomal recessive disorder caused by an impaired Na⁺/I^- symporter (NIS)-mediated active iodide accumulation into thyrocytes. We analyze the presence of NIS gene mutations in six patients with congenital hypothyroidism, goiter and reduced or absent ^99mTcO4^- uptake. Genomic DNA encoding NIS sequence was evaluated. The analysis revealed the presence of an undescribed homozygous C to T transition at position -54 located in the 5�f untranslated region in one patient. Functional analysis performed in NIS cDNA wild-type (WT) or mutated (-54C�¨T)-transfected COS-7 cells showed that the mutant only concentrated 10% of WT levels (¹²⁵Iodide), suggesting a direct role of the mutation as cause of ITD. The mutation severely impaired NIS protein expression (Western blot). NIS mRNA levels (RT/qPCR) were similar in the carrying NIS mutated sequence and WT cells, favoring a translational deficiency exerted by the mutation. NIS mRNA polysomal profile analysis in transfected cells demonstrated a significantly reduced mutant NIS mRNA levels in polysomes, consistent with a reduced translation rate and a subsequent reduced protein expression. Moreover, our results support the possibility that alterations of proteins related to NIS targeting to the plasma membrane could also account as potential causes of ITD.