The connexin gene family codes for the protein subunits of gap junction channels that mediate direct diffusion of ions and metabolites between the cytoplasm of adjacent cells. Both GJB2 and GJB6 genes are located in the DFNB1 locus and co-expressed in the inner ear. About 50% of non-syndromic hearing loss patients have mutations in the GJB2 gene, however, a large fraction of patients (10-42%) only carry one mutation in the GJB2 gene. In a study of 33 non-syndromic prelingual hearing loss patients (Del Castillo et al. 2002), 22 were found to carry heterozygous mutation in both the GJB2 and GJB6 gene. A digenic model of GJB2 and GJB6 mutations was suggested for the mechanisms of non-syndromic hearing loss. The 232kb and 309kb deletions are the common mutations found in the GJB6 gene. However, certain patients carry one mutation in the GJB2 gene but do not carry the common deletion. GJB6 sequencing is available as the next step in testing for these patients, following Connexin 30 (GJB6) Deletion Testing. Connexin 30 (GJB6) deletion testing and Connexin 30 (GJB6) sequence analysis are also included on our Hearing Loss Panel.
Point mutations of GJB6 have been reported in dominant hearing loss patients. In addition, point mutations of GJB6 gene can cause hydrotic ectodermal dysplasia (Clouston Syndrome). This disease is an autosomal dominant skin disorder characterized by palmoplantar hyperkeratosis, hair defects (from partial to total alopecia), nail hypoplasia, and nail deformities. For detection of the point mutations associated with Clouston syndrome, specify GJB6 sequence analysis and the indication for testing on the requisition.
Indications for Testing
- Non-syndromic hearing loss, negative for GJB2 sequencing
- Non-syndromic hearing loss, negative for GJB6 deletion mutations
- Clinical confirmation of Clouston Syndrome
- Family history with previous identified mutation in GJB6 gene
OMIM Number: 300502
Sample requirements
- Infants: 2-3 mL whole blood in purple top EDTA tube
- Children (>2 years) and Adults: 5 mL whole blood in purple top EDTA tube
Sample Handling: Blood samples stored overnight should be refrigerated or kept cold. Blood samples should never be frozen. Specimens being sent from outside facilities should be packaged with a cold pack according to standard medical safety practices. The specimen should be shipped by overnight priority [scheduled to arrive by Friday AM at the latest].
Shipping Address: Center for Human Genetics Laboratory
10524 Euclid Ave, 6th Floor
Cleveland, OH 44106
216-983-1134
For local samples, please call the Center for Human Genetics Laboratory (216-983-1134) to arrange for sample pick-up.
Turn Around Time: 3 weeks
Cost/CPT Codes: $657.70 / 83890, 83898 (x2), 83894 (x2), 83904 (x4), 83909 (x4), 83912