title: Prevalence, Incidence Proportion, and Heritability for Tinnitus: A Longitudinal Twin Study.
abstract: The purpose of this longitudinal twin study was to explore the effect of tinnitus on hearing thresholds and threshold shifts over two decades and to investigate the genetic contribution to tinnitus in a male twin cohort (n = 1114 at baseline and 583 at follow-up). The hypothesis was that participants with faster hearing deterioration had a higher risk for developing tinnitus and there is an underlying role of genetic influences on tinnitus.
  
  
  
  Male mono- and dizygotic twin pairs, born between 1914 and 1958 were included. Mixed models were used for comparison of hearing threshold shifts, adjusted for age. A co-twin comparison was made within pairs discordant for tinnitus. The relative influence of genetic and environmental factors was estimated by genetic modeling.
  
  
  
  The overall prevalence of tinnitus was 13.5% at baseline ((Equation is included in full-text article.)age 50) and 34.4% at follow-up ((Equation is included in full-text article.)age 67). The overall incidence proportion was 27.8%. Participants who reported tinnitus at baseline or at both time points were older. At baseline, the hearing thresholds differed between tinnitus cases and controls at all frequencies. New tinnitus cases at follow-up had the greatest hearing threshold shift at the high-frequency area compared with the control group. Within pairs, the tinnitus twin had poorer hearing than his unaffected co-twin, more so for dizygotic than monozygotic twin pairs. The relative proportion of additive genetic factors was approximately 0.40 at both time points, and the influence of individual-specific environment was 0.56 to 0.61. The influence of genetic factors on tinnitus was largely independent of genetic factors for hearing thresholds.
  
  
  
  Our hypotheses were confirmed: The fastest hearing deterioration occurred for new tinnitus cases. A moderate genetic influence for tinnitus was confirmed.
authors.affiliation: 1Department of Clinical Science, Intervention and Technology, Section of Audiology, Karolinska Institutet, Huddinge, Sweden; 2Department of Audiology and Neurotology, Karolinska University Hospital, Huddinge, Sweden; 3Public Health Agency of Sweden, Stockholm, Sweden; 4Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; and 5Department of Medical Sciences, Occupational and Environmental Medicine Uppsala University, Uppsala, Sweden.
authors.forename: Renata
authors.initials: R
authors.lastname: Bogo
authors.forename: Ahmed
authors.initials: A
authors.lastname: Farah
authors.forename: Kjell K
authors.initials: KK
authors.lastname: Karlsson
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Magnus
authors.initials: M
authors.lastname: Svartengren
authors.forename: Åsa
authors.initials: Å
authors.lastname: Skjönsberg
mesh_terms: D000328:Adult; D000368:Aged; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold; D016022:Case-Control Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D015995:Prevalence; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014012:Tinnitus / Q000453:epidemiology / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic