title: Two puzzling cases of thyroid dysgenesis.
abstract: BACKGROUND
  In the last couple of years, different genes that play major roles in embryonic thyroid development have been identified. Several mutations, e.g., NKX2.1, FOXE1 and PAX8, were identified in patients with congenital hypothyroidism due to thyroid dysgenesis. However, the pathophysiology of most cases of thyroid dysgenesis remains unknown. Due to the sporadic occurrence and discordance observed in monozygotic twins, a classic genetic hypothesis for thyroid dysgenesis is improbable.
  
  
  METHODS
  We present two pairs of monozygotic twins discordant for thyroid dysgenesis that exemplify these conceptual difficulties.
  
  
  CONCLUSIONS
  Identification of the epigenetic differences observed in monozygotic twins discordant for thyroid dysgenesis may be crucial in discovering the pathogenesis of thyroid dysgenesis.
authors.affiliation: Institute of Experimental Paediatric Endocrinology, Charité, Berlin, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Kuehnen
authors.forename: A
authors.initials: A
authors.lastname: Grueters
authors.forename: H
authors.initials: H
authors.lastname: Krude
mesh_terms: D002648:Child; D002675:Child, Preschool; D003409:Congenital Hypothyroidism / Q000175:diagnosis / Q000209:etiology; D004200:Diseases in Twins / Q000175:diagnosis; D005260:Female; D006801:Humans; D008297:Male; D050033:Thyroid Dysgenesis / Q000150:complications / Q000175:diagnosis*; D013961:Thyroid Gland / Q000000981:diagnostic imaging; D014430:Twins, Monozygotic; D014463:Ultrasonography