Identification and characterization of four PAX 8 rare sequence variants (p.T225R, p.L233L, p.G336S and p.A439A) in patients with congenital hypothyroidism and dysgenetic thyroid glands.

SEBASTIÁN A ESPERANTE, CARINA M. RIVOLTA, LUCRECIA MIRAVALLE, VIVIANA HERZOVICH, SONIA IORCANSKY, MARCO BARALLE, HÉCTOR M. TARGOVNIK

CLINICAL ENDOCRINOLOGY

Blackwell Publishing

Lugar: Oxford; Año: 2008 vol. 68 p. 828 - 835

0300-0664

Context: Thyroid dysgenesis is associated with mutations in the PAX8 gene and is characterized by congenital hypothyroidism transmitted in an autosomal dominant mode. Objetives: The aim of this study was to identify new mutations in the PAX8 gene. 60 congenital hypothyroidism-affected individuals with dysgenetic (agenesis, ectopia and hypoplasia) and eutopic thyroid glands were studied. Methods: The 12 exons of the PAX8 gene along with their exon-intron boundaries were amplified from genomic DNA and a mutational screening was performed by single-strand conformational polymorphism (SSCP) followed by direct sequencing of samples with abnormal migration patterns. The PAX8 mutations were functionally characterized by transient transfection experiments. Results: The molecular analysis of the PAX8 gene indicates that four affected individuals have four  rare sequence variants: three novel variations (c.699C>T [p.L233L], c.1006G>A [p.G336S] and c.1317A>G [p.A439A]) and one recently reported (c.674C>T [p.T225M]), whereas the 56 remaining patients show only wild-type alleles of PAX8. All variations were not detected in the general population, suggesting that these changes are not polymorphisms. Functional analysis of the nonsynonymous substitutions showed that the PAX8T225M and PAX8G336S proteins  have not lost their abilities to bind a specific DNA sequence and to activate the transcription of the TG promoter in synergy with titf1. Conclusions: We report the ocurrence of two nonsynonymous, one recently reported and one novel,  and two novel synonymous substitutions in the PAX8 gene in individuals with congenital hypothyroidism and dysgenetic thyroid glands. p.T225M  and p.G336S are rare sequence variants or in an expeculative fashion, may act inhibiting an unknown particular function. In addition, our study confirms the very low prevalence of PAX8 mutations in thyroid dysgenesis.