Approximately 1 out of every 2000 infants is born profoundly deaf, and more than one-third of people born with normal hearing will have a significant hearing loss by their 60s. Hearing loss has a variety of causes, including trauma (such as a head injury), illness (such as rubella or meningitis), the environment (notably, long-term exposure to loud noise), drugs (including some powerful chemotherapy agents and certain antibiotics), genetics, or some combination of these factors. Genetic hearing loss has not been well understood until recently, when several of the responsible genes were identified. The hearing loss that results from inherited defects in these genes can be divided into syndromic and nonsyndromic.