Non-Syndromic (Genetic) Hearing Loss

Definition and epidemiology

Hereditary hearing losses are called “non-syndromic” when no additional finding (vision, kidney, heart involvement, etc.) accompanies them, and “syndromic” when they occur with other system findings. About 70% of genetic hearing losses are non-syndromic.

Permanent hearing loss in newborns occurs in about 1-3 per 1000 births, and a significant portion is of genetic origin (Korver et al., 2017). Inheritance is most often autosomal recessive; these forms are usually congenital and more severe.

The most common single genetic cause is changes in the GJB2 gene (Connexin 26 protein); this protein is involved in maintaining potassium balance in the inner ear (Kenneson et al., 2002).

Symptoms and signs

In congenital forms the baby does not respond to sound, does not turn to their name, and shows delayed speech-language development. Thanks to screening programmes, most cases are detected in the newborn period before symptoms appear.

Some genetic forms are mild at birth but can be progressive; hearing may decrease gradually as the child grows. The loss is usually bilateral and sensorineural.

Because it is non-syndromic, no health problem other than hearing is expected; this is important for distinguishing it from syndromic forms.

Causes and risk factors

More than a hundred genes have been associated with non-syndromic hearing loss; these loci are named DFNB for recessive forms and DFNA for dominant forms. GJB2 is the most common cause.

Consanguineous marriage increases the frequency of autosomal recessive forms; therefore, a history of consanguinity and hearing loss in the family are important risk indicators.

Genetic counselling is valuable for informing families about the mode of inheritance, recurrence risk and diagnostic options (Shearer et al., 2017).

Audiological and clinical assessment

The process begins with newborn hearing screening; babies who do not pass are referred for advanced audiological assessment. The aim is to confirm the hearing loss as early as possible.

• Newborn screening: OAE and/or automated ABR.
• Diagnostic ABR and ASSR: determine frequency-specific hearing thresholds in babies.
• Behavioural audiometry: applied as the child grows and confirms thresholds.
• Genetic testing: targeted or panel tests, especially for GJB2, confirm the diagnosis and help predict prognosis.

Additional assessments such as an eye examination and, where needed, ECG and imaging may be planned to exclude syndromic causes.

Treatment and audiological rehabilitation

The core approach is early amplification and intensive auditory-language rehabilitation. The international target is to complete screening by 1 month, diagnosis by 3 months and rehabilitation by 6 months (the 1-3-6 principle).

For mild-to-severe losses, appropriately fitted hearing aids are the first choice. In severe-to-profound losses with insufficient benefit from a device, a cochlear implant is considered; in cochlear-origin forms such as GJB2, implant outcomes are usually very good.

The success of rehabilitation depends largely on starting early and on family involvement; auditory-verbal therapy and language support are continued throughout the process.

Impact on quality of life and advice

Early diagnosis and rehabilitation can keep the child’s language, academic and social development close to that of peers. Late diagnosis, on the other hand, can lead to permanent delays in language development.

Families are advised to have genetic counselling, set realistic expectations and maintain regular follow-up. Because hearing loss can be progressive, periodic re-assessment of device settings and hearing is important.