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Genetic factors are the major causes of childhood hearing impairment. Whereas autosomal recessive mutations account for the majority of prelingual non-syndromic sensorineural hearing impairment (NSSHI), the relative contribution of mitochondrial DNA (mtDNA) mutations to childhood onset NSSHI has not been established. We screened 202 subjects with congenital/childhood onset NSSHI, consisting of 110 sporadic cases, 75 sib pairs, and 17 families with affected subjects in more than one generation, in order to determine the prevalence of mtDNA mutations associated with NSSHI. mtDNA mutations were found in three of 10 families (30%) in whom the affected members were related through the maternal lineage. One sporadic case (0.9%) was also found to have a known mtDNA mutation but none was found in the sib pairs. Although the prevalence of mtDNA mutations was low in the group as a whole (2%), we suggest that screening should be considered in cases of childhood hearing impairment when it is progressive and particularly in families where transmission is compatible with maternal inheritance. Keywords: mitochondrial DNA; point mutation; hearing impairment

We describe a family with non-syndromic sensorineural hearing impairment inherited in a manner consistent with maternal transmission. Affected members were found to have a novel heteroplasmic mtDNA mutation, T7510C, in the tRNASer(UCN) gene. This mutation was not found in 661 controls, is well conserved between species, and disrupts base pairing in the acceptor stem of the tRNA, making it the probable cause of hearing impairment in this family. Sequencing of the other mitochondrial tRNA genes did not show any other pathogenic mutations. Four other mutations causing hearing impairment have been reported in the tRNASer(UCN) gene, two having been shown to affect tRNASer(UCN) levels. With increasing numbers of reports of mtDNA mutations causing hearing impairment, screening for such mutations should be considered in all cases unless mitochondrial inheritance can be excluded for certain. Keywords: hearing impairment; mtDNA mutation; tRNASer(UCN)

Editor—Deafness is the most frequent sensory impairment in humans, with significant social and psychological implications. At least half of all cases of permanent childhood hearing impairment have a genetic cause.1 However, there is almost universal agreement among clinical geneticists that only a small proportion of such families are referred to clinical genetics services.2 Increasing public awareness of genetics in general will lead to increased demand. Therefore, what do families want and how should genetic services be planned? Between September 1997 and October 1998, the parents of 522 hearing impaired children, aged between 4 and 13 years, in the Trent Health Region, were sent a questionnaire, which comprised 10 questions about their experience and opinion of clinical genetic services (see Appendix). The families had been identified in a previous geographically defined, population based ascertainment study of childhood hearing impairment.3 A further 104 families identified by that study were excluded from the questionnaire survey because (1) they had indicated an unwillingness to participate in further research, (2) they were lost to follow up, (3) the child had died, or (4) a local professional had indicated an approach would not be appropriate. The majority (n=416) of families were also sent an invitation to take part in a home visit, to investigate clinical aspects of non-syndromal hearing impairment. Those not invited to participate in a home visit (n=106) were the families of children who had a named syndrome (with hearing impairment as a recognised association) or who had a definite diagnosis of meningitis. Eighty two families were visited as part of this aspect of the study. (These data are to be published elsewhere.) Data from the previous study3 indicated that those not approached in the questionnaire survey were significantly less likely …