title: A new PAX8 mutation causing congenital hypothyroidism in three generations of a family is associated with abnormalities in the urogenital tract.
abstract: BACKGROUND
  Although thyroid dysgenesis is the most common cause of congenital hypothyroidism (CH), its molecular basis remains largely elusive. Indeed, in only a minority of cases with thyroid dysgenesis (2%-3%) was it possible to identify an underlying genetic defect. The objective of this study was to screen the PAX8 gene and the PAX2 gene in a family with six cases of CH spanning three generations and presenting urogenital malformations. Herein, we report a case series and in vitro characterization of the PAX8 gene mutation.
  
  
  METHODS
  Investigations were conducted at a tertiary care referral center. The index case was diagnosed to have congenital hypothyroidism at 7 months of age when he presented with severe impairment of suckling, constipation, and poor development. Treatment with levothyroxine corrected the symptoms and was associated with catch-up growth. His progeny, including two sons, one daughter, and two granddaughters, were affected by CH, and three of them received the diagnosis at neonatal screening. Ultrasound demonstrated normally located thyroid glands with reduced volumes. Five of the six affected family members, including the index case, had urogenital malformations, including incomplete horseshoe kidney, undescended testicles, hydrocele, and ureterocele. Strabismus was found in three out of six affected patients. No other somatic malformations were found.
  
  
  RESULTS
  Direct sequencing of the PAX8 gene revealed a new heterozygous mutation (c.74C > G) in all affected individuals. This mutation leads to substitution of proline with arginine at codon 25 (P25R). Fluorescence microscopy showed that P25R is normally located in the nucleus. In transient transfection studies, this mutation causes reduced transcriptional activation ability when using a luciferase reporter construct under the control of a thyroglobulin promoter. This diminished transactivation ability is due to loss of DNA binding capability as shown in electrophoresis mobility shift assay. The sequencing analysis of the PAX2 gene was normal.
  
  
  CONCLUSIONS
  We conclude that this novel PAX8 mutation is responsible for a severe form of dominantly inherited CH. The mutation seems to be associated with abnormalities of the urogenital tract.
authors: 1 Department of Pediatrics, Hospital of Divino Espirito Santo , Ponta Delgada, Portugal .
authors: Ana
authors: A
authors: Carvalho
authors: Pia
authors: P
authors: Hermanns
authors: Ana-Luísa
authors: AL
authors: Rodrigues
authors: Isabel
authors: I
authors: Sousa
authors: João
authors: J
authors: Anselmo
authors: Hennie
authors: H
authors: Bikker
authors: Rita
authors: R
authors: Cabral
authors: Carlos
authors: C
authors: Pereira-Duarte
authors: Luísa
authors: L
authors: Mota-Vieira
authors: Joachim
authors: J
authors: Pohlenz
mesh_terms: D000328:Adult; D002675:Child, Preschool; D003409:Congenital Hypothyroidism / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics*; D004252:DNA Mutational Analysis; D020022:Genetic Predisposition to Disease; D006367:HeLa Cells; D040941:Heredity; D006579:Heterozygote; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009154:Mutation; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics* / Q000378:metabolism; D010375:Pedigree; D010641:Phenotype; D013974:Thyroxine / Q000627:therapeutic use; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D016896:Treatment Outcome; D014564:Urogenital Abnormalities / Q000175:diagnosis / Q000235:genetics*
chemical_list: D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors; D013974:Thyroxine