Contribution of the N-acetyltransferase 2 polymorphism NAT2*6A to age-related hearing impairment.

BACKGROUND: Age-related hearing impairment (ARHI) is the most common sensory impairment in older people, affecting 50% of those aged 80 years. The proportion of older people is increasing in the general population, and as a consequence, the number of people affected with ARHI is growing. ARHI is a complex disorder, with both environmental and genetic factors contributing to the disease. The first studies to elucidate these genetic factors were recently performed, resulting in the identification of the first two susceptibility genes for ARHI, NAT2 and KCNQ4. METHODS: In the present study, the association between ARHI and polymorphisms in genes that contribute to the defence against reactive oxygen species, including GSTT1, GSTM1 and NAT2, was tested. Samples originated from seven different countries and were combined into two test population samples, the general European population and the Finnish population. Two distinct phenotypes for ARHI were studied, Z(low) and Z(high), representing hearing in the low and high frequencies, respectively. Statistical analysis was performed for single polymorphisms (GSTM1, GSTT1, NAT2*5A, NAT2*6A, and NAT2*7A), haplotypes, and gene-environment and gene-gene interactions. RESULTS: We found an association between ARHI and GSTT1 and GSTM1 in the Finnish population sample, and with NAT2*6A in the general European population sample. The latter finding replicates previously published data. CONCLUSION: As replication is considered the ultimate proof of true associations in the study of complex disorders, this study provides further support for the involvement of NAT2*6A in ARHI.

Familial aggregation of tinnitus: a European multicentre study.

INTRODUCTION AND AIM: Tinnitus is a common condition affecting approximately 20% of the older population. There is increasing evidence that changes in the central auditory system following cochlear malfunctioning are responsible for tinnitus. To date, few investigators have studied the influence of genetic factors on tinnitus. The present report investigates the presence of a familial effect in tinnitus subjects. METHODS: In a European multicentre study, 198 families were recruited in seven European countries. Each family had at least 3 siblings. Subjects were screened for causes of hearing loss other than presbyacusis by clinical examination and a questionnaire. The presence of tinnitus was evaluated with the question "Nowadays, do you ever get noises in your head or ear (tinnitus) which usually last longer than five minutes". Familial aggregation was tested using three methods: a mixed model approach, calculating familial correlations, and estimating the risk of a subject having tinnitus if the disorder is present in another family member. RESULTS: All methods demonstrated a significant familial effect for tinnitus. The effect persisted after correction for the effect of other risk factors such as hearing loss, gender and age. The size of the familial effect is smaller than that for age-related hearing impairment, with a familial correlation of 0.15. CONCLUSION: The presence of a familial effect for tinnitus opens the door to specific studies that can determine whether this effect is due to a shared familial environment or the involvement of genetic factors. Subsequent association studies may result in the identification of the factors responsible. In addition, more emphasis should be placed on the effect of role models in the treatment of tinnitus.

Working memory and novel word learning in children with hearing impairment and children with specific language impairment.

BACKGROUND: Working memory is considered to influence a range of linguistic skills, i.e. vocabulary acquisition, sentence comprehension and reading. Several studies have pointed to limitations of working memory in children with specific language impairment. Few studies, however, have explored the role of working memory for language deficits in children with hearing impairment. AIMS: The first aim was to compare children with mild-to-moderate bilateral sensorineural hearing impairment, children with a preschool diagnosis of specific language impairment and children with normal language development, aged 9-12 years, for language and working memory. The special focus was on the role of working memory in learning new words for primary school age children. METHODS & PROCEDURES: The assessment of working memory included tests of phonological short-term memory and complex working memory. Novel word learning was assessed according to the methods of. In addition, a range of language tests was used to assess language comprehension, output phonology and reading. OUTCOMES & RESULTS: Children with hearing impairment performed significantly better than children with a preschool diagnosis of specific language impairment on tasks assessing novel word learning, complex working memory, sentence comprehension and reading accuracy. No significant correlation was found between phonological short-term memory and novel word learning in any group. The best predictor of novel word learning in children with specific language impairment and in children with hearing impairment was complex working memory. Furthermore, there was a close relationship between complex working memory and language in children with a preschool diagnosis of specific language impairment but not in children with hearing impairment. CONCLUSIONS: Complex working memory seems to play a significant role in vocabulary acquisition in primary school age children. The interpretation is that the results support theories suggesting a weakened influence of phonological short-term memory on novel word learning in school age children.

Hearing impairment among adults--extent of the problem and scientific evidence on the outcome of hearing aid rehabilitation.

Scientific surveys on current and estimated prevalence of hearing impairment (HI) in adult populations (> or = 18 years of age) in Denmark, Finland, Norway, Sweden and the United Kingdom, and scientific reports on the outcome of hearing aid (HA) rehabilitation worldwide were reviewed. Only a few of the studies meet strict scientific criteria, and many locally clinically relevant studies cannot be generalized to larger populations. Population-based studies indicate an increase in prevalence of HI with age, but because of differences in study populations and available national population statistics, the studies do not allow reliable comparisons between countries or estimation of future prevalence of HI. Studies on HA prescription or outcomes do not provide uniform data in favour of non-linear amplification, but they do show some subject preference for the newer technology. No conclusions can be drawn regarding the degree of HI and the effects of amplification. The literature review alone gives only limited information regarding the extent of the problem of HI in adult populations in the target countries. Similarly, only a few studies on HA outcome meet strict scientific criteria and even fewer studies correlate rehabilitation outcome with the degree of HI, disability or handicap.

Objective assessment of hearing aid use.

Hearing aid use was assessed using both objective (time recorded in the memory of the hearing aid) and subjective methods (interview and patient diary) in a clinical series of consecutive adult female and male Finnish and Norwegian hearing aid candidates (n = 84). The median study time was 34 days (minimum 21, maximum 73). Over a third of the subjects used their hearing aid for less than 4 hours a day according to an objective assessment. Both of the subjective methods tended to overestimate the use. This preliminary study shows that an objective assessment of hearing aid use is needed and the subjective methods must be validated.

Linguistic and motor abilities of low-birthweight children as assessed by parents and teachers at 8 years of age.

UNLABELLED: Linguistic and motor abilities among low-birthweight 8-y-old children in the northern Finland Birth Cohort for 1985-1986 (n = 9322) were studied using parental and teacher evaluations. The parents of 8370 (90%) and teachers of 8525 (92%) children returned a mailed questionnaire concerning the children's speech, language, learning and motor abilities. Low-birthweight (LBW, < 2500 g) children (n = 279) appeared to have experienced more difficulties than normal-birthweight (NBW, > or = 2500 g) children (n = 8091). The parents evaluated the LBW boys to be the poorest in linguistic and motor skills compared with the other boys or any of the groups of girls. They are therefore presumably at risk of having problems at school, which was confirmed by the teachers' reports. There was also a clear relationship between speech/linguistic and motor disabilities. CONCLUSION: Multivariate logistic regression analyses showed that the lower birthweight and some sociodemographic factors, for example the mother's age being between 20 and 24 y, having more than four children in the family, a reconstructed family, as well as hearing impairment and male gender were the most important determinants of poor speech and language abilities at 8 y of age, with and without adjustment for neonatal risk factors (asphyxia, convulsions, respiratory distress syndrome, bronchopulmonary dysplasia, patent ductus arteriosus). Smallness for gestational age was also a risk factor for poor speech and language skills. Preterm birth was associated with poor skills only after adjustment for the neonatal risk factor. The parental and teacher evaluations were concordant concerning the LBW children's outcome.

Can the impact of hearing impairments be modelled?

The effects of two simulated hearing impairments (presbyacusis) on speech perception were investigated in two groups of normally hearing subjects (30 and 48 subjects, respectively). Eight patients with presbyacusis with similar hearing impairment to those in the latter simulation served as the clinical material. Word recognition scores were measured in quiet and in cocktail party noise (S/N + 18 dB and + 12 dB). The recognition scores deteriorated in the less favourable listening conditions. Somewhat surprisingly, the hearing impaired subjects showed better word recognition scores in quiet and especially in moderate noise. Subjective complaints on speech perception difficulties in noise on a visual analogue scale behaved quite logically; the hearing impaired subjects' subjective experiences were no milder than those of the normally hearing during the simulation. The better results in word recognition shown by the hearing aid candidates may be explained by habituation to the hearing impairment.

Aetiology and risk indicators of hearing impairments in a one-year birth cohort for 1985-86 in northern Finland.

The aetiology and risk indicators of hearing impairments of all types and degrees were studied in a 1-year birth cohort of 8713 children from northern Finland. The subjects (7 years of age) included in the clinical and audiometric examinations were recruited by standard clinical criteria, i.e. suspicion of parents according to a questionnaire, abnormal hearing screening result or a hearing impairment noted in hospital records (n = 541), and by random sampling from among the 8172 not suspected (n = 1009). One-hundred-and-one subjects in the group suspected of having hearing impairment and 27 subjects in the random sample eventually had hearing impairment. The aetiology could be defined in only 44.5% of the cases, ear infections being the most common. In this relatively small series, only a few risk indicators (congenital anomalies, meningitis and a history of ear discharge lasting for over 1 month) could be shown to be associated with impaired hearing in a logistic regression analysis.

Hearing and occupation.

Not only does the environment play a role as a source of risk factors for a hearing impairment, but a hearing impairment itself can adversely affect interaction with family members, workmates and friends, thus reducing social well-being. The number of work-related hearing impairments has been decreasing for last five years, but noise-induced sensorineural hearing loss is still the second most common work-related disease in Finland. The financial burden related to occupational hearing impairments includes costs of compensation, salaries of screening personnel, equipment, maintenance costs, costs resulting from loss of work for the employer and referrals to specialist clinics etc, which until now have not been calculated in Finland. Numerous questions still remain to be answered regarding the association of age, socioacousis, occupation and leisure activities with the development of sensorineural hearing impairment. Can hearing impairment acquired in childhood or in early adolescence predict the development of occupational hearing loss? What is the interactive role of such factors as ageing, chemicals, diet, environmental noise, genetic susceptibility and the individual's other diseases in the development of noise-induced hearing impairment?

Epidemiology of moderate to profound childhood hearing impairments in northern Finland. Any changes in ten years?

The epidemiology of childhood hearing impairments was studied in a clinical series of the birth cohorts for 1973-82 and 1983-92 from a geographically well-defined area. The overall prevalence of hearing impairments with PTA0.5-4 kHz > or = 40 dB was 1.2/1000 live births. Even in the later cohort, the median age ascertainment was 2.6 years for the congenital or early acquired group and 3.0 years for all impairments. Risk indicators for hearing impairment were present in half of the children, and those referred for the risk were ascertained at the median age of 1.1 years. The delay from suspicion to ascertainment was over a year in about one fifth of cases, while the median time from referral to ascertainment was only 1.8 months. The planning and implementation of neonatal hearing screening are suggested, and general information is given on paedoaudiology for both parents and professionals. A database could be beneficial in increasing the systemacy of the diagnostic process.

Conditions for paediatric hearing screening: a survey in 28 Finnish child welfare clinics.

The present Finnish paediatric hearing screening programme was assessed by interviewing nurses and doctors in 28 child welfare clinics responsible for the hearing screening of 18,500 preschool children. Practical issues which might have effects on both performing the screenings and referring the children with abnormal screening results were emphasised. This survey brought out a great variety of deficiencies, which may contribute to the existing delayed diagnosis of hearing impairments. Hearing screening was routinely done 4-12 times per child before school age, instead of the 3 times recommended. Methods with a nonspecific frequency range and sound pressure level were often used. Audiometers were only used in 22 of the 28 clinics, and in only 9 clinics were the audiometers calibrated yearly. The median time of working in the child health care field at that particular health centre was 7 y for the nurses and 6 y for the doctors. Both the nurses and the doctors had numerous responsibilities other than paediatric hearing screening. Implementation of an updating training programme in paediatric audiology for the personnel is recommended.

Effect of hearing impairment on educational outcomes and employment up to the age of 25 years in northern Finland.

The association between hearing impairment in adolescence and school performance and the outcome of education was studied among 25-year-old subjects followed since pregnancy in the Northern Finland birth cohort. The series, 395 subjects with abnormal hearing and 977 randomly selected controls, was based on a questionnaire on hearing and school achievement sent to 11780 members of the cohort alive at the age of 14 years, and on audiometric screening test requested from health centers. Hearing loss was defined as 'clinically significant' if the pure tone average (PTA; mean of the thresholds at 0.5, 1 and 2 kHz) exceeded 25 dB in the better ear; a threshold of > or = 30 dB at 4 kHz and a PTA of < or = 25 dB as '4 kHz loss'; and as 'slightly abnormal' if any of the thresholds exceeded 20 dB at any frequency and the case did not belong to the above two categories. The more severe the hearing impairment, the poorer was the child's performance at elementary school. Those with normal hearing and those with a slightly abnormal or 4 kHz loss were equally often accepted for intermediate education (88%), while those with a clinically significant loss had the lowest acceptance figures (64%). When adjusting for neurological and social confounders, excluding mental disability, the risk of not qualifying from intermediate or higher education at all was twice as high among those with a clinically significant loss as among the controls (OR 2.1, 95% CI 1.13-3.8), and was still elevated after adjustment had been made for all the relevant perinatal, neurological and social factors (OR 1.9, 95% CI 1.02-3.6). 14% of those with a clinically significant hearing loss, 9% of the subjects with a 4 kHz loss and 7% of those with normal hearing were unemployed at the age of 25 years. Hearing impairment appears to have effects on both the outcome of education and employment status.

More education in paediatric audiology needed for child welfare clinic nurses and doctors.

Opinions on formal and further education in paediatric audiology were surveyed by interviewing nurses and doctors in 28 Finnish child welfare clinics. Over half of the nurses recalled that they had been taught hearing screening during their period of practical training. Regarding formal teaching in paediatric audiology, the majority of doctors referred to courses in either otolaryngology, paediatrics or both. None of the doctors and only three of the nurses had taken part in any updating courses dealing with paediatric audiology during the last three years, and it turned out that no such courses had been arranged in three of the five hospital districts. However, 17 out of the 27 doctors and 23 out of the 28 nurses expressed their interest in further education. The present amount of formal education in paediatric audiology was ascertained from all five Finnish medical faculties and the five nursing schools in the provinces of Oulu and Lapland. The university departments of otolaryngology carry the major responsibility for teaching in paediatric audiology, which includes one to two hours of lectures and none to four hours of tutorials, depending on the faculty concerned. The amount of audiometric training at nursing schools varies from none to five hours and that of lectures in otolaryngology from three to twenty hours. Better co-ordination between departments of otolaryngology, general practice and paediatrics is needed when arranging teaching in paediatric audiology for medical students. Trainee child welfare nurses seem to need more guided practice in audiometry, and there is an obvious need for increasing the amount of practice in audiological departments. Specialist clinics should plan and implement a programme for updating training in paediatric audiology, including evaluation of the programme.

Prevalence figures for mild hearing impairments cannot be based on clinical data.

The target population of the present study consisted of a 1-year (July 1985-June 1986) birth cohort from northern Finland. The prevalence of even slight hearing impairments (any threshold from 0.5 to 4 kHz > or = 25 db) at the age of 7 years was investigated among those 8,713 children still living in the area. The subjects for clinical audiometry were obtained in two ways. First, the standard clinical practice brought about 541 children, either with non-confirming results from their child welfare clinic screenings, suspected by their parents or already diagnosed as hearing impaired at a hospital. Secondly, in addition to this group, a random sample of 1,009 children, out of the 8,172 children not suspected, were also invited for audiometry. Of the clinical material, 101 children out of the 438 investigated were found to have impaired hearing according to the above criteria, and another 27 children out of the 789 investigated were obtained from the random sample. The estimated over-all prevalence of hearing impairments, even with the slight ones included, turned out to be 3.9% (95% confidence interval, CI, 2.7-5.7). Only 32% of the hearing impairments could be obtained according to the standard clinical policy! In conclusion, one cannot rely on clinical data when calculating prevalence figures for mild hearing impairments.

Hearing in 55 to 75 year old people in northern Finland--a comparison of two classifications of hearing impairment.

A total of 5,400 persons from different age groups was randomly selected from the population register for the study, and of the 1,620 55 to 75 year old persons invited, 1,233 attended the check-ups (76.1%). Air conduction pure tone thresholds were measured at the frequencies of 0.25, 0.5, 1, 2, 3, 4, 6 and 8 kHz. The findings were interpreted according to both the EU and WHO classifications. According to the WHO classification, 1,046 subjects (85.0%) had normal hearing and 124 persons (10.1%) had a mild hearing impairment, 44 (3.6%) a moderate, 13 (1.1%) a severe and 3 (0.2%) had a profound hearing impairment. According to the EU classification, 758 subjects (61.6%) were found to have normal hearing, a mild impairment was observed in 363 persons (29.5%), a moderate hearing impairment in 96 (7.8%) and a severe impairment in 13 (1.1%) persons. None had a profound hearing impairment. The difference between these classifications is remarkable as is evident in even this small study. A thorough discussion on the role of different gradings for hearing is needed.

Otitis media and long-term follow-up of hearing.

The present material is based on a birth cohort of 2,512 children followed up from the antenatal period. Data on middle ear infections were collected until the children were 7 years. At the age of 7, audiometry was performed on 298 of them. For reasons other than middle ear infection, 32 children were excluded and the final material comprised 266 children. Only those children with clear differences in their history for otitis media were analysed. Although the pure tone averages (0.5-3 kHz) showed no major changes, different mean air-conduction (AC) thresholds were associated with different histories of otitis media. The 35 healthy children (with no otitis media episodes until 2 years of age) showed the best mean AC thresholds. The 51 children with recurrent acute otitis media (RAOM; > or = 4 episodes of acute otitis media) showed worse thresholds at the high frequencies and those 13 who had had secretory otitis media (SOM) at all frequencies. The children with a history of otitis media, either RAOM or SOM, more often had hearing thresholds exceeding 20 dB. Our results might indicate inner ear involvement in these long-term follow-up hearing thresholds.