title: Prevalence and etiology of congenital or early acquired hearing impairment in Eastern Finland.
abstract: OBJECTIVE
  The purpose of this study was to determine the prevalence and etiology of congenital or early acquired bilateral sensorineural hearing impairment (SNHI) in children born from 1988 to 2002 in the district of Kuopio University Hospital, Finland, and to compare the results with those from an earlier 14-year period in the same region and similar population.
  
  
  METHODS
  The data were collected retrospectively from Hospital Records. The degree of hearing impairment was based on average air conduction threshold calculated over the frequencies 0.5, 1, 2 and 4 kHz in the better hearing ear. Hearing impairment was classified as mild (≥ 20-39 dB), moderate (40-69 dB), severe (70-95 dB) and profound (>95 dB).
  
  
  RESULTS
  We identified 92 children with bilateral SNHI diagnosed before the age of 7 years. The overall prevalence and the prevalence for at least moderate SNHI was 2.1 per 1000 live births and 1.2 per 1000 live births, respectively. We found no differences in the prevalence of SNHI during both study periods. Etiology was genetic in 46%, acquired in 14% and unknown in 40%. Out of the genetic cases 74% were non-syndromic and 26% were syndromic. In comparison to the previous study there was a decline in the proportion of acquired SNHI and the proportion of genetic and unknown cause had increased. Six children in five families had homozygous 35delG mutation and six children in four families presented with a homozygous M34T mutation.
  
  
  CONCLUSIONS
  The prevalence of congenital or early acquired SNHI in the Kuopio University Hospital district area has not changed during a period of 29 years. Despite possibility to test the GBJ2 gene, the proportion of hearing impairment of unknown etiology remained high.
authors.affiliation: Department of Otorhinolaryngology, Kuopio University Hospital, PO Box 1777, FIN-70211 Kuopio, Finland. aarno.dietz@kuh.fi
authors.forename: Aarno
authors.initials: A
authors.lastname: Dietz
authors.forename: Tuija
authors.initials: T
authors.lastname: Löppönen
authors.forename: Hannu
authors.initials: H
authors.lastname: Valtonen
authors.forename: Antti
authors.initials: A
authors.lastname: Hyvärinen
authors.forename: Heikki
authors.initials: H
authors.lastname: Löppönen
mesh_terms: D017677:Age Distribution; D017668:Age of Onset; D001299:Audiometry / Q000379:methods; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D016208:Databases, Factual; D005260:Female; D005387:Finland / Q000453:epidemiology; D006312:Hearing Loss, Bilateral / Q000151:congenital / Q000453:epidemiology* / Q000209:etiology*; D006319:Hearing Loss, Sensorineural / Q000151:congenital / Q000453:epidemiology* / Q000209:etiology*; D006801:Humans; D066298:In Vitro Techniques; D007223:Infant; D008297:Male; D015995:Prevalence; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D017678:Sex Distribution