Hearing loss in children with mitochondrial disorders.

Objective: At least 1-5 children per 1000 suffer from congenital hearing loss, and 50% of these cases can be attributed to genetic causes. It has been estimated that 1% of pre-lingual hearing loss is due to mutations in mitochondrial DNA. Previous literature reports audiometric data for few patients, usually less than 20 per study. The goal of this study was to characterize the hearing loss associated with mitochondrial mutations and determine whether previously characterized patterns of hearing loss in these patients (progressive, sensorineural, high frequency losses) are found in our population as well.

Methods: An IRB-approved retrospective chart review of the electronic medical records in the Nemours/Alfred I. dupont Hospital for Children system from January 2004 to October 2009 (a five-year period) was undertaken using ICD-9 codes 277.87 (mitochondrial disorder) and 359.89BA (mitochondrial myopathy). These 149 records were then evaluated for audiologic data, resulting in 26 charts with both a mitochondrial disorder and hearing evaluation.

Results: Of 26 patients with known mitochondrial disorders and audiometric documentation, 15 (58%) had hearing loss, and 11 patients had normal hearing (42%). Ten patients had sensorineural hearing loss (38%), two patients had conductive hearing loss (7.7%), one patient had a mixed hearing loss (3.8%), and two patients had an as yet undefined hearing loss (ABR had not yet been performed at the time of this study) (7.7%).

Conclusion: In comparison with previous studies, generally including less than 20 patients, this is one of the largest collections of audiometric data on children with mitochondrial disorders. Unlike prior studies describing a progressive, sensorineural loss across all frequencies or mainly affecting high frequencies, the hearing loss in our patients was more variable including low frequency losses, mid-frequency losses, and conductive losses and was often not progressive or even improved. Our overall 38% rate of sensorineural hearing loss correlates well with previous case series; this study clearly justifies the use of routine audiometric screening in children with mitochondrial disorders, including use of ABR and OAEs as ASND can be seen in this population, as well as repeat testing over time to evaluate for progression.