title: Mutations in the NKX2.5 gene and the PAX8 promoter in a girl with thyroid dysgenesis.
abstract: BACKGROUND
  Screening of the known candidate genes involved in thyroid organogenesis has revealed mutations in a small subset of patients with congenital hypothyroidism due to thyroid dysgenesis (TD).
  
  
  OBJECTIVE
  We studied a girl with TD who had mutations in two transcription factors involved in thyroid development.
  
  
  RESULTS
  Sequencing analysis of candidate genes involved in thyroid gland development revealed a new paternally inherited heterozygous mutation in the NKX2.5 gene (S265R) and a new maternally inherited heterozygous mutation in the PAX8 promoter region (-456C>T). Both parents and a brother, who was also heterozygous for both mutations, were phenotypically normal. Immunofluorescence microscopy showed a correct nuclear localization of both wild-type (WT) and mutant NKX2.5 proteins. EMSA demonstrated that the mutant NKX2.5 binds to the NKE_2, DIO2, TG, and TPO promoter elements equally well as the WT protein. However, the mutant NKX2.5 protein showed a 30-40% reduced transactivation of the thyroglobulin and the thyroid peroxidase promoters and a dominant-negative effect of the mutant NKX2.5. EMSA studies of the WT and mutant PAX8 promoter sequences incubated with nuclear extracts from PCCL3 cells exhibited a loss of protein binding capacity of the mutant promoter. In addition, the mutant PAX8 promoter showed a significantly reduced transcriptional activation of a luciferase reporter gene in vitro. Thus, this promoter mutation is expected to lead to reduced PAX8 expression.
  
  
  CONCLUSIONS
  We identified new heterozygous mutations in both NKX2.5 and PAX8 genes of a girl with TD. Both defects might contribute to the phenotype.
authors: Department of Pediatrics, Johannes Gutenberg University Medical School, Langenbeckstrasse 1, D-55101 Mainz, Germany.
authors: Pia
authors: P
authors: Hermanns
authors: Helmut
authors: H
authors: Grasberger
authors: Samuel
authors: S
authors: Refetoff
authors: Joachim
authors: J
authors: Pohlenz
mesh_terms: D003409:Congenital Hypothyroidism / Q000235:genetics*; D005260:Female; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D009154:Mutation; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics*; D011401:Promoter Regions, Genetic; D050033:Thyroid Dysgenesis / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; C095552:NKX2-5 protein, human; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors; D014157:Transcription Factors