title: Causes of permanent childhood hearing impairment.
abstract: BACKGROUND
  The causes of Permanent Childhood Hearing Impairment (PCHI) are often quoted as being hereditary in 50%, acquired in 25%, and unknown in 25% of cases. Interest in the causes of PCHI has grown recently due to increasing diagnostic possibilities. We investigated the evidence for the reported distribution of these causes.
  
  
  METHODS
  Population-based study and a systematic review. Inclusion criteria for population-based study: children born between 2003 and 2005, resident in The Netherlands at birth, known at an Audiology Center with PCHI at the age of 3-5 years. The causes of PCHI were determined prospectively by detection of congenital cytomegalovirus on dried blood spots and/or genetic diagnostic investigations in addition to reviewing data from medical records. A systematic review was carried out using three terms (hearing loss, infant, and etiology) and limited to articles published between January 1997 and July 2009. Main outcome measures were: the (weighted) proportions of the various causes of PCHI following diagnostic investigations.
  
  
  RESULTS
  In the study-population (n = 185) a hereditary cause was found in 38.9%, acquired cause in 29.7%, miscellaneous cause in 7.1%, and the cause remained unknown in 24.3%. The systematic review of the literature (n = 9 articles) resulted in a weighted mean of 30.4% hereditary, 19.2% acquired, and 48.3% unknown causes of PCHI.
  
  
  CONCLUSIONS
  The systematic review and the results of the population-based study provided little support for the generally accepted distribution of causes of PCHI.
authors.affiliation: Willem-Alexander Children and Youth Center, Subdepartment of Social Pediatrics, Leiden University Medical Center, Leiden, The Netherlands. a.m.h.korver@lumc.nl
authors.forename: Anna M H
authors.initials: AM
authors.lastname: Korver
authors.forename: Ronald J C
authors.initials: RJ
authors.lastname: Admiraal
authors.forename: Sarina G
authors.initials: SG
authors.lastname: Kant
authors.forename: Friedo W
authors.initials: FW
authors.lastname: Dekker
authors.forename: Capi C
authors.initials: CC
authors.lastname: Wever
authors.forename: Henricus P M
authors.initials: HP
authors.lastname: Kunst
authors.forename: Johan H M
authors.initials: JH
authors.lastname: Frijns
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Oudesluys-Murphy
mesh_terms: D002675:Child, Preschool; D003586:Cytomegalovirus Infections / Q000150:complications; D034381:Hearing Loss / Q000209:etiology* / Q000235:genetics; D006801:Humans; D009426:Netherlands; D011446:Prospective Studies