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GJB2 Sequencing, Full Gene Sequencing

Specimen Whole blood, buccal swab, amniotic fluid, or chorionic villus sample (CVS) (Submission of maternal blood is required for fetal testing.)
Volume 7 mL whole blood, 4 buccal swabs, 10 mL amniotic fluid, or 20 mg CVS
Minimum Volume 3 mL whole blood, 2 buccal swabs, 5 mL amniotic fluid, or 10 mg CVS
Container Lavender-top (EDTA) tube or yellow-top (ACD) tube; sterile plastic conical tube, two confluent T-25 flasks for fetal testing; or LabCorp buccal swab kit
Storage Instructions Maintain specimen at room temperature or refrigerate at 4°C.
Causes for Rejection Frozen specimen; hemolysis; quantity not sufficient for analysis; improper container; wet buccal swab
Use Detects mutations in the coding region and noncoding first exon of the connexin 26 (GJB2) gene associated with nonsyndromic sensorineural hearing loss (NSHL)
Limitations This test does not detect variants in any other gene, nor does it detect genomic deletions or promoter or deep-intron variants. Molecular-based testing is highly accurate, but as in any laboratory test, rare diagnostic errors may occur.
Methodology DNA sequencing
Additional Information Connexin 26 is one of the most significant genes involved in congenital, nonsyndromic, sensorineural hearing loss (NSHL, OMIM 220920) (GJB2, OMIM 121011). Connexin 26 produces a protein that directs the intracellular transfer of ions and molecules that are important in hearing. Mutations in the connexin 26 gene (GJB2) can account for 50% of NSHL in some populations. This type of hearing loss is inherited in an autosomal-recessive manner. The two most common mutations, 35delG (also called 30delG) and 167delT, have been found in many, but not all, different ethnic groups with varying detection rates. In US Caucasians, 35delG has been reported in more than 66% of cases of recessive nonsyndromic sensorineural hearing loss. In the Ashkenazi Jewish population, 35delG and 167delT are responsible for more than 70% of cases. One or both mutations have been reported in European, Russian, Mediterranean, Arab, South American, Israeli, and Pakistani populations. At this time, these mutations have not been found in reported studies of Asian Americans or African Americans.
References Dong J, Katz DR, Eng CM, Kornreich R, Desnick RJ. Nonradioactive detection of the common connexin 26 167delT and 35delG mutations and frequencies among Ashkenazi Jews. Mol Genet Metab. 2001 Jun; 73(2):160-163.PubMed 11386851

Milunsky JM, Maher TA, Yosunkaya E, Vohr BR. Connexin-26 gene analysis in hearing-impaired newborns. Genet Test. 2000; 4(4):345-349.PubMed 11216657

Scott DA, Kraft ML, Carmi R, et al. Identification of mutations in the connexin 26 gene that cause autosomal recessive nonsyndromic hearing loss. Hum Mutat. 1998; 11(5):387-394.PubMed 9600457

Smith RJH, Van Camp G. Nonsyndromic hearing loss and deafness, DFNB1. GeneReviews. 2008 Sep 28 (updated 2011 Jul 14). Available at http://www.ncbi.nlm.nih.gov/books/NBK1272. Accessed September 10, 2009.PubMed 20301449

Sobe T, Vreugde S, Shahin H, et al. The prevalence and expression of inherited connexin 26 mutations associated with nonsyndromic hearing loss in the Israeli population. Hum Genet. 2000; 106(1):50-57.PubMed 10982182