Application of Next-Generation–Sequencing in Hearing Loss Diagnosis

Abstract

Hearing loss is the most common birth defect and sensorineural disorder in humans. Hearing loss results from obstructions in the transmission of the sound anywhere between the outer ear and auditory cortex in the brain. In a normal condition, the sound signal that is collected by the outer ear is amplified by the middle ear for transmission to the cochlea, which then converts this energy into electrical signals that are ultimately transmitted to the brain through the auditory nerves (Smith et al. 1993). Based on the defective anatomical structure involved, hearing loss can be classified as conductive, sensorineural, or mixed. Conductive hearing loss is a defect in conducting sound waves through outer and middle ear due to abnormalities of outer ear, tympanic membrane (eardrum), or ossicles of the middle ear. Sensorineural hearing loss (SNHL) is due to a defect located anywhere from cochlea to the auditory cortex. Mixed hearing loss is a combination of both conductive and sensorineural abnormalities. Depending on the age at onset, hearing loss can be classified as prelingual, present before speech development, or postlingual, present after speech development. Severity of the hearing loss is measured by decibels (dB), can be graded from mild (26–40 dB) to profound (90 dB), affecting from low to high frequencies (Smith et al. 1993).