Medical genetic evaluation for the etiology of hearing loss in children

Advances in genetic manipulations in the treatment of hearing disorders

Gene transfer into the inner ear is an attractive technology for clinical applications. It offers the hope of preventing, arresting, reversing or curing vestibular or hearing disorders caused by hereditary diseases or environmental insults. There are currently very few treatment options for vestibular disorders and sensorineural hearing loss, and therefore, it is important to investigate and develop new technologies for inner ear disease. In utero gene transfer may indeed be an option, but this technology will have many technical and ethical issues that remain to be overcome.

Systematic review of the etiology of bilateral sensorineural hearing loss in children

OBJECTIVE

Identification of the etiology of sensorineural hearing loss (SNHL) in children facilitates management and provides important prognostic information. In recent years, the etiology of bilateral SNHL in children has changed due to advances in genetic testing and treatment of perinatal infections. The objective of this study was to determine the frequency of etiologies of moderate-profound bilateral sensorineural hearing loss (SNHL) in children.

METHODS

The English literature was searched in Medline for articles published between 1966 and 2002. The inclusion criteria were studies involving bilateral SNHL >/=40dB in children less than 18 years of age. The studies were required to account for all patients, and provide a breakdown of etiologic factors. Etiologies investigated included genetic and non-genetic (prenatal, perinatal, postnatal). To compare differences between the frequencies of etiologies a two-sample t-test was performed assuming unequal variance. Studies were stratified according to perceived confounders: start date of study, study design, and degree of hearing loss.

RESULTS

Seven hundred and eighty abstracts were screened for relevancy. Forty-three studies satisfied the inclusion criteria. The common etiologies of bilateral SNHL were unknown (41.5%), genetic non-syndromic (27.2%), prenatal (11.5%), perinatal (9.7%), postnatal (6.6%), and genetic syndromic (3.5%). Unknown and Rubella were significantly less frequent etiologies in the more recent studies, while genetic non-syndromic, asphyxia and prematurity were more common. Genetic non-syndromic hearing loss was more frequent in the prospective studies compared to the population and retrospective studies, but this difference was not significant. Genetic non-syndromic hearing loss was more common among patients with profound hearing loss.

CONCLUSION

Accounting for the recent decline in infectious etiologies, the most common causes of bilateral SNHL are unknown (37.7%), genetic non-syndromic (29.2%), prenatal (12%), perinatal (9.6%), postnatal (8.2%), and genetic syndromic (3.2%).

Relationships between neurologic disorders and hereditary hearing loss

Hearing loss is a common disorder that often has a neurologic etiology. Recently, there has been significant progress in the discovery of the genes that cause sensorineural hearing loss, and this has led to increased understanding of the pathophysiology of both syndromic and nonsyndromic hearing problems. These genes cover the range of processes involved in neurologic development and function, including structural genes, transcription factors, and tumor suppressors; genes involved in signal transduction processes, such as ion homeostasis and intracellular transport; and mitochondrial genes responsible for oxidative phosphorylation and energy production. Interactions between genes as well as between genes and environmental factors have also been documented. Understanding of these processes should lead to earlier and more accurate diagnosis and more effective treatment for neurologic disorders and hearing loss.