title: Heritability of hearing loss.
abstract: BACKGROUND
  Hearing impairment is one of the most common permanent disabilities in the western world. Although hearing ability normally declines with age, there is great individual variation in age of onset, progression, and severity, indicating that individual susceptibility plays a role. The aim of the present study was to explore the relative importance of genetic and environmental effects in the etiology of impaired hearing.
  
  
  METHODS
  From August 1995 to June 1997, the total adult population of Nord-Trøndelag County, Norway, was invited to take part in the Nord-Trøndelag Health Study. The survey included as an integrated project the Nord-Trøndelag Hearing Loss Study with pure-tone audiometry assessment of the standard frequencies 0.25, 0.5, 1, 2, 3, 4, 6, and 8 kHz on 51,574 participants aged 20 to 101 years. We obtained information from Statistics Norway identifying 11,263 sibling pairs. After age stratification, we assessed similarity in hearing thresholds between siblings using polychoric correlations. The contribution of genetic effects in hearing ability was calculated.
  
  
  RESULTS
  The upper limit of the heritability of hearing loss was 0.36. We found little evidence for sex differences in the relative importance of genetic effects.
  
  
  CONCLUSIONS
  There is a substantial genetic contribution to individual variation in hearing thresholds.
authors.affiliation: Division of Mental Health, Norwegian Institute of Public Health, Oslo, Norway. ellen.kvestad@fhi.no
authors.forename: Ellen
authors.initials: E
authors.lastname: Kvestad
authors.forename: Nikolai
authors.initials: N
authors.lastname: Czajkowski
authors.forename: Norun Hjertager
authors.initials: NH
authors.lastname: Krog
authors.forename: Bo
authors.initials: B
authors.lastname: Engdahl
authors.forename: Kristian
authors.initials: K
authors.lastname: Tambs
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001299:Audiometry; D001309:Auditory Threshold; D005260:Female; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease / Q000453:epidemiology; D034381:Hearing Loss / Q000453:epidemiology / Q000209:etiology / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D012737:Sex Factors; D055815:Young Adult