The auditory system contains the inner ear that is responsible for transforming the mechanical energy of the sound waves into electrical stimuli, which is translated in the brain. The auditory system is composed of a cochlea, which is a fluid-filled tube coiled in a spiral shape around the modiolus.
Hearing impairment has a wide spectrum of etiologies originating from both environmental and genetic factors. Genetic factors of hearing defects, poses greater challenges. A hearing disability that appears early in childhood can have a major consequence on language acquisition. Hearing loss is categorized based on the frequency loss and the severity of hearing thresholds. When hearing loss is the only apparent abnormality, it is referred to as non-syndromic hearing loss (NSHL). In other cases, hearing loss occurs along with a variety of other malformations and thus is designated as syndromic hearing loss (SHL). Panoply of genes have been discovered to be involved in hearing loss.
To date, more than 50 genes and 80 additional loci have been linked to various degrees of hearing impairment. Hearing loss can be passed by autosomal dominant, autosomal recessive, X-linked, Y-linked, and mitochondrial mode of inheritance.
Figure from Dror AA and Avraham KB. Neuron , 2010