Background

In England the birth prevalence of bilateral per manent childhood hearing impairment (PCHI) of> 40 dB HL is approximately 1: 1000 live births but almost doubles up to the age of 9 years. 1 The latter is accounted for by cases of PCHI that were not screened as part of the Newborn Hearing Screening Programme (NHSP) or were false nega tives, as well as children with acquired hearing loss and those with late onset or progressive deafness. In some areas the prevalence can be two to three times this figure. 2 About 40% of children with PCHI have additional health or developmental problems, and about 20% of this population have more than two problems. 3 In the developed world, at least 50% of PCHI has a genetic aetiology with environmental causes (which may include adverse perinatal factors, for example, extreme prematurity, hyperbilirubinaemia, aminoglycoside drugs, hypoxia, meningitis and congenital infections) and head trauma accounting for a further 25%. In the remaining 25% no cause for the deafness is found following aetiological investigation. 4