Non-syndromic Hearing Loss: GJB2 / GJB6 Analysis

Diagnostic Use

The incidence of congenital, prelingual hearing loss is approximately one in 1000 births. Of these, one in four are classified as non-syndromic. Defects in GJB2, which is located on the long arm of chromosome 13 and encodes the protein Connexin 26, are responsible for the most common form of non-syndromic sensorineural deafness type 1 (DFNB1).

DFNB1 is an autosomal recessive form of sensorineural hearing loss which results from damage to the neural receptors of the inner ear, the nerve pathways to the brain, or the area of the brain that receives sound information. Approximately 98% of affected individuals are homozygous or compound heterozygous for mutations in the GJB2 gene. The deletion of a single guanosine (G) residue within a stretch of six G’s at position 30-35 in the GJB2 gene (c.35delG) leads to premature chain termination and is present in 40-70% of DFNB1 patients (approximate population carrier frequency 1:40 to 1:100).

In a further 2% of DFNB1 patients, heterozygosity for a GJB2 mutation and a 342kb deletion affecting part of the GJB6 gene (encoding the Connexin 30 protein) is observed. A single mutation involving the splicing site of the non-coding exon 1 of GJB2 is an infrequently reported variant.

Department

Genetics - Molecular Pathology

Delphic Registration Code

MOLP

Constituent Tests

• Genomic DNA Extraction

Synonyms

Connexin 26 Gene Analysis
DFNB1 sequencing
GJB2 sequencing
GJB6 sequencing

Turnaround Time

4 weeks

Test Code

4193

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

4.0

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

1.0

Minimum Sample Volume (ml)

0.5

Additional Specimen Information

This genetic test needs nucleated cells. Please don’t centrifuge or freeze the EDTA blood tube.

Aliquot Instructions

Sample Type

• Whole Blood

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

Please don’t centrifuge or freeze the EDTA blood tube.

Test Method

The entire coding exon of the GJB2 gene is analysed by DNA sequencing, and gap-PCR is performed to detect the 342kb deletion affecting the GJB6 gene. This combination detects mutations in nearly 100% of individuals with a diagnosis of DFNB1, the commonest form of non-syndromic autosomal recessive deafness.

Non-Funded Test Cost

$233.32 (Exclusive of GST)

Billing Code

4193

Uncertainty of Measurement:
Automated bidirectional DNA sequencing has an analytical sensitivity and specificity of >99%. Note that the lower limit of variant detection of sequencing analysis is ~10%, this is important to consider in the case of mosaicism, mitochondrial, and somatic variation that is not expected to be present at 50% or 100%. This analysis will not detect variants located within intronic regions, except at the intron-exon boundaries.

Genomic DNA must be extracted from samples prior to testing. This incurs an additional charge (see GDNA). Laboratories may prefer to submit DNA for testing. Please provide a minimum of 5 micrograms of DNA at 20 nanograms / microlitre.

Contact Information

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