Profound Permanent Hearing Impairment in Childhood: Causative Factors in Two European Countries

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Abstract
A collaboration between Denmark and Wales was established in order to evaluate any differences between countries in factors causing permanent childhood hearing impairment (PCHI). Two identical 6-year birth-cohorts from 1975-1980 suffering from a permanent hearing loss >90 dB HL in the better hearing ear, averaged across 0.5-4 kHz (BEHL), were included in the analysis. The overall estimated prevalence of children with this loss was 0.41/live births in Wales (n = 59). In Denmark the overall prevalence was 0.45/1,000 live births (n = 34), there being no significant differences in prevalence between the two countries. Both cohorts were subjected to a multidisciplinary investigation protocol. No significant differences were found between countries in the proportion of hearing impairment caused by the various factors, when based on uniform criteria and identical birth-cohorts. The proportion of inherited hearing loss is 47-50% in the two countries. Within inheritance the proportion of non-syndromal/syndromal inheritance differs slightly, as non-syndromal inheritance comprises 50% in Wales, and 76% in Denmark. The reported proportion of 16-34% of unknown factors causing profound PCHI emphasises the need for appropriate protocols for aetiological evaluation.