Analysis of the PAX8 gene in 32 children with thyroid dysgenesis and functional characterization of a promoter variant.
BACKGROUND
The molecular basis underlying the development of thyroid dysgenesis remains largely unknown. The objective of this study was to analyze the PAX8 gene in 32 children with congenital hypothyroidism due to thyroid dysgenesis for mutations, and to characterize the functional consequences of the mutations.


METHODS
The 5'-untranslated region and the entire coding region of the PAX8 gene were analyzed in 32 children. Functional analyses with a reporter gene assay were performed in transfected PCCL3 and TSA cells.


RESULTS
Thirty children did not have any sequence alterations. Two individuals had a previously identified monoallelic cytosine to thymine transition at position -983 in the promoter (-983C>T; mutant P. A of the ATG of the initiator codon is designated as +1), and a novel guanine to cytosine transversion in the non-coding exon 1 (-465G>C; mutant E). Functional analysis revealed that the basal transcriptional activity of the mutants is decreased compared to the wild type. Gel mobility shift assays indicated that mutant P does not interact with a transacting factor whose nature remains to be elucidated. The DNA binding property of mutant E were similar compared to the wild type.


CONCLUSIONS
These results suggest that mutations in PAX8 are most likely a very rare cause of thyroid dysgenesis. The observed sequence alterations result in diminished transcriptional activity and, in conjunction with other genetic and non-genetic modifiers, they may contribute to the pathogenesis of thyroid hypoplasia and hypothyroidism.
Denise
D
Perone
Geraldo
G
Medeiros-Neto
Célia Regina
CR
Nogueira
Antonio José
AJ
Chagas
Vera Maria
VM
Alves Dias
Maria Fátima
MF
Viana
Peter
P
Kopp
D020121:5' Untranslated Regions; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics*; D010375:Pedigree; D011401:Promoter Regions, Genetic; D013959:Thyroid Diseases / Q000235:genetics*
D020121:5' Untranslated Regions; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors