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Paediatric Laboratory Medicine

Hearing Loss - Non-Syndromic, Autosomal Recessive: GJB2 Sequencing

Clinical Significance

Non-syndromic sensorineural hearing loss (NSHL) is a common disability affecting approximately 1 in 1000 newborns. In approximately 50% of children with congenital deafness the hearing loss is due to inherited causes. The most common form of inherited hearing loss is autosomal recessive non-syndromic hearing loss (AR-NSHL), which affects approximately 1 in every 2500 children.

Many different genes have been shown to play a role in NSHL.Mutations in the in the GJB2 gene have been implicated in 50 to 80% of AR-NSHL cases, making this the most common cause of AR-NSHL. The GJB2 gene encodes a gap junction protein called connexin 26, which is important in the development of the inner ear. A second gap junction protein, connexin 30 encoded by the GJB6 gene, can also cause AR-NSHL. In particular a recurrent deletion in the GJB6 gene (delGJB6-D13S1830) has been reported to cause AR-NSHL in approximately 20% of patients who also have one GJB2 gene mutation.

The strategy used for testing for non-syndromic hearing loss is complete sequencing of the coding region and flanking exon/intron boundaries of the GJB2 gene, and direct mutation testing for the recurrent deletion mutation (delGJB6-D13S1830) in the GJB6 gene.

Test Name

Hearing Loss - Non-Syndromic, Autosomal Recessive: GJB2 Sequencing

Gene Name

  • GBJB2

Alternate Gene Name

CX26, CX30

Test Code

DEAFN

Division

Molecular Genetics

Method

Sequencing

External Proficiency Testing

CAP

Turn Around Time

2 weeks (Prenatal samples), 2-3 weeks (Pregnancy/Urgent samples), 4-6 weeks (Routine)

Protein

Gap junction protein, beta 2; Connexin 26

Disease/Condition

Hearing Impairment: Non-Syndromic, Autosomal Recessive

Specimen Type

Blood; extracted DNA is not accepted for GJB6 Deletion/Duplication Analysis.

If sending a prenatal sample, please contact the laboratory prior to sending sample to discuss sample requirements.

For details about specimen requirements, please refer to: Specimen Type & Requirements (PDF).

Minimum Specimen Requirements

5-10 mL EDTA or ACD 0.5 mL EDTA (neonate); minimum 10 ug in 100 uL low TE (pH8.0)

Storage/Transportation

Room Temperature

Special Requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

Approval is not required

CPT Codes

479252

Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Canada
Phone: 416-813-7200
Phone: 1-855-381-3212

Interpretation

Interpretation is provided in report