Deafness (GJB2-related, mild/moderate)

Overview

GJB2-related deafness refers to inherited hearing loss caused by changes in the GJB2 gene. This condition is responsible for a significant proportion of non-syndromic hearing loss, which means the hearing impairment is not accompanied by other signs or symptoms affecting different body parts. It is considered one of the most common causes of genetic hearing loss globally. The degree of hearing loss can vary, typically presenting as mild to moderate [PMID:16380302]. The hearing loss is usually sensorineural, affecting the inner ear's ability to process sound.

Symptoms & clinical features

Individuals with GJB2-related deafness commonly experience hearing loss that is present from birth (congenital) or develops very early in life. The severity can range from mild, where soft sounds are difficult to hear, to moderate, where conversational speech might be missed without amplification. The hearing loss is generally stable, meaning it does not typically worsen over time, though some variability has been observed [PMID:11812836]. In most cases, both ears are affected similarly (bilateral involvement), though asymmetric hearing loss or even unilateral involvement has been reported in rare instances. Importantly, individuals with this type of hearing loss do not typically have other associated health issues.

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Affected organs

The primary organ affected by GJB2-related deafness is the inner ear, specifically the cochlea, which is responsible for converting sound vibrations into nerve impulses. The GJB2 protein, also known as connexin 26, plays a crucial role in the normal functioning of the cochlea by forming channels that allow the transport of essential ions, like potassium, necessary for hearing [PMID:11812836]. Pathogenic changes in GJB2 disrupt this process, leading to impaired hearing.

Multiple body systems

Systemic involvement

Cellular impact

Mechanism at cellular level

Risks & severity

The severity of GJB2-related hearing loss mainly ranges from mild to moderate. In rare instances, severe or profound hearing loss can occur, particularly when specific types of genetic changes are present or in combination with variants in related genes [PMID:16380302]. The hearing loss is usually stable and non-progressive, meaning it typically does not worsen with advancing age. Because this condition is non-syndromic, individuals generally do not face increased risks for other health complications. The exact prevalence of GJB2-related deafness is not precisely established for the UK population, but it is recognised as a common cause of inherited hearing loss.

Genetic causes

Deafness related to the GJB2 gene is caused by pathogenic changes in the GJB2 gene. This gene provides instructions for making a protein called connexin 26. Connexin 26 is vital for creating channels (gap junctions) that span the membranes of cells in the inner ear. These channels allow small molecules and ions, particularly potassium ions, to pass between cells. This transport is crucial for maintaining the electrical environment needed for hair cells in the cochlea to send sound signals to the brain. When the GJB2 gene has pathogenic changes, the connexin 26 protein may be faulty or absent, disrupting these vital channels and leading to impaired hearing [PMID:11812836]. The GJB2 gene is associated with conditions including DFNB1 (autosomal recessive non-syndromic hearing loss type 1A) and DFNA3 (autosomal dominant non-syndromic hearing loss type 3A).

• GJB2
  gap junction protein beta 2
  The GJB2 gene provides instructions for producing the gap junction beta 2 protein, critical for cell-to-cell communication, particularly in the inner ear and skin.

Inheritance pattern

GJB2-related deafness can be inherited in a few different ways, but most commonly it follows an autosomal recessive pattern. This means an individual usually inherits two pathogenic copies of the GJB2 gene, one from each parent, to develop the condition. Parents who each carry one pathogenic copy typically do not have hearing loss themselves but are called 'carriers'. If both parents are carriers, there is a 1 in 4 (25%) chance with each pregnancy that their child will inherit two pathogenic copies and develop hearing loss. Less commonly, GJB2-related deafness can also be inherited in an autosomal dominant pattern. In this case, inheriting just one pathogenic copy of the GJB2 gene is sufficient to cause hearing loss. In dominant inheritance, a child has a 1 in 2 (50%) chance of inheriting the condition if one parent has a pathogenic variant. Genetic counselling can help families understand their specific inheritance risks.

Diagnosis & testing

Diagnosis of GJB2-related deafness typically begins with a clinical evaluation of hearing loss, often identified through newborn hearing screening programmes in the UK. Further audiometric testing will precisely characterise the degree and type of hearing loss. A definitive diagnosis is then confirmed through genetic testing, which looks for pathogenic changes in the GJB2 gene. Referral for genetic testing is usually made by a clinical geneticist, an ear, nose, and throat (ENT) specialist, or an audiology specialist. Genomic testing for inherited deafness is available within the NHS Genomic Medicine Service (GMS) and is managed under specific R-codes, such as R257 for non-syndromic hearing loss. Genetic counsellors play a key role in explaining the testing process, results, and implications for the individual and their family.

Management & lifestyle

Management of GJB2-related deafness focuses on optimising hearing and supporting communication development. As the hearing loss is typically mild to moderate and non-progressive, interventions often include hearing aids to amplify sounds. For some individuals with severe hearing loss, cochlear implants might be considered, though this is less common for typical GJB2-related cases. Speech and language therapy, as well as educational support, are important to help children develop strong communication skills. Regular audiology appointments will monitor hearing levels and ensure hearing devices are properly fitted and adjusted. Management plans are tailored to individual needs and are developed in collaboration with a multidisciplinary team including audiologists, ENT specialists, and educators, all accessible through the NHS.

UK care pathway

In the UK, individuals with suspected inherited hearing loss are typically referred through their GP or paediatrician to audiology services and possibly an Ear, Nose, and Throat (ENT) specialist. If a genetic cause is suspected, referral to a clinical genetics service is the standard pathway. These services can arrange for genomic testing, often using specific NHS Genomic Medicine Service R-codes like R257 for non-syndromic hearing loss. Genetic counsellors are integral to this pathway, providing essential information and support regarding genetic testing, inheritance patterns, and the implications for families.

Related conditions

While GJB2-related deafness is typically non-syndromic, meaning hearing loss is the only symptom, it's important to distinguish it from other forms of inherited hearing loss. Other genetic causes of hearing loss can be syndromic, meaning they are part of a broader condition with multiple symptoms affecting different body systems, such as Usher syndrome or Pendred syndrome. Hearing loss can also be acquired, meaning it develops after birth due to factors like infection, injury, or noise exposure, rather than being inherited. Genetic testing helps to accurately identify the specific cause of hearing loss.

Frequently asked questions