Hearing loss

Hearing loss is a symptom of an underlying pathologic change to the auditory system rather than a diagnosis in itself. It is characterised by type (conductive, sensorineural, mixed, or central auditory dysfunction), onset (congenital, prelingual, postlingual, adult-onset, or presbycusis), severity (mild to profound), affected frequencies, laterality, and audioprofile. Onset spans a wide spectrum: autosomal recessive nonsyndromic forms are typically prelingual and severe-to-profound, whereas autosomal dominant nonsyndromic forms are usually postlingual, progressive, and high-frequency.

The clinical presentation is further divided into nonsyndromic forms, which are not associated with visible abnormalities of the external ear or with manifestations involving other organs, and syndromic forms, which combine hearing loss with malformations of the external ear or with findings involving other organ systems. Approximately 20% of children initially presenting with apparent nonsyndromic hearing loss are subsequently diagnosed with a syndromic form, reflecting the evolving nature of the clinical phenotype.

The estimated prevalence is approximately 1.33 per 1,000 newborns with permanent congenital hearing loss, rising to approximately 3.5 per 1,000 by adolescence. In developed countries, approximately 65% of prelingual hearing loss is attributed to genetic causes.

The genetic conditions associated with hereditary hearing loss follow heterogeneous inheritance patterns. Among individuals with nonsyndromic genetic hearing loss, approximately 80% follow autosomal recessive inheritance, approximately 19% autosomal dominant, and less than 1% X-linked or mitochondrial; for postlingual nonsyndromic genetic hearing loss, autosomal dominant inheritance predominates.

• Where hereditary hearing loss is suspected to have a genetic cause, molecular genetic testing can identify the underlying condition and confirm a clinical suspicion.
• The identified entity guides further clinical management and is a prerequisite for targeted medical care; therapeutic options are evaluated individually by the treating physicians.
• Identification of the underlying pathogenic germline variant enables predictive testing of at-risk family members and provides information relevant to family planning.

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