Connexin 26

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CONNEXIN 26

Gene Symbol: GJB2
 
Protein: Gap Junction Beta-2 Protein
 
Chromosomal Locus: 13q11-q12
 
Pseudonyms: CX26, DFNB1A, DFNA3A
 
TURNAROUND TIME: 10 business days
 
TESTING METHODOLOGY: Polymerase chain reaction (PCR) & DNA sequencing of exon 2 of the GJB2 gene.
 
SPECIMEN REQUIREMENTS:
  • Collect: Prefer two 5ml whole blood EDTA (lavender top) tube.
  • Min. Collection: 0.7 ml whole blood EDTA.
  • Transport: blood EDTA at Room Temp shipped regular next day air (No Saturday delivery; store specimen at 40°C and ship Monday).
  • Stability: Ambient: up to 7 days; Refrigerated: 2 weeks. Frozen: unacceptable
  • Unacceptable Conditions: Serum. Frozen or severely hemolyzed blood. Clotted blood.
  • Prenatal testing: Direct: 5ml direct unspun amniotic fluid or 15mg CVS tissue with a backup flask growing. Culture: confluent T25 flask. Maternal blood sample is required for maternal cell contamination studies.

A Molecular Genetics Laboratory Test Requisition must accompany the specimen. Contact the Molecular Laboratory at 918-502-1721 to obtain further information.

Note:
Counseling and informed consent are recommended for genetic testing; Center for Genetic Testing at Saint Francis consent form is available as a resource but not required.
 
INTERPRETATIVE DATA:
 
Incidence (of congenital hearing loss): 1 to 6 in 1000
 
Inheritance: Of inherited forms, 70-80% is autosomal recessive, 23-30% is dominant, and 2-3% is X-linked. The GJB2 gene can cause recessive (DFNB1) or dominant (DFNA3) forms of hearing loss. DFNB1 accounts for approximately 50% of all congenital, severe-to-profound, ARNSHL in the United States.
 
Disease Characteristics: Significant hearing loss
 
Molecular Genetic Mechanism: A variety of missense, nonsense and insertion/deletion mutations have been described in the gene.
 
 
Clinical Sensitivity: 98% for DFNB1; 90% for DFNA3; 50% for all "congenital, severe to profound autosomal recessive non-syndromic hearing loss"- ARNSHL.
 
Analytic Sensitivity: >99%
 
Test Limitations: mutations outside exon 2 will not be detected (<1% of mutations).
 
INDICATIONS FOR USE:
  • To determine the genetic basis for hearing loss in an affected individual.
  • Isolated hearing loss in a family
  • Individuals at risk due to family history who wish prenatal diagnosis.
ADDITIONAL RESOURCES:
 
Genetics Home Reference: ghr.nlm.nih.gov/gene/GJB2
Gene Reviews for DFNA3: www.ncbi.nlm.nih.gov/books/NBK1536
Gene Reviews for DFNB1: www.ncbi.nlm.nih.gov/books/NBK1272