About 1 in 1000 young children have a major hearing impairment (threshold >80dB).  Significant hearing loss also occurs in about 1 in 25 people under age 45, and 1 in 10 by age 60 (threshold >25dB). Most of the hearing loss has been localized to defects in a single gene, Connexin 26 (Cx26) on chromosome 13q11-12. A variety of mutations have been described in this gene with a 35delG hotspot mutation representing over half of the defects in Caucasians.

Recently a second gene locus, Connexin 30 (Cx30), has been identified that can also cause recessive hearing loss. Cx30 is located very close to Cx26 on chromosome 13 and is co-expressed as a prerequisite for proper development of the cochlea. The most important finding is that hearing loss can be a result of a compound heterozygote, with a single mutation in each gene.

Aminoglycoside-induced, and nonsyndromic sensorineural deafness has been associated in some cases with an A1555G mutation in the mitochondria (12S DNA). The deafness can have either a congenital or late onset presentation,  and affected individuals may not have been exposed to the antibiotic. The incidence of this mutation is not well known but may represent a small percentage of affected individuals that show no signs of Connexin 26 defects.  In maternally inherited forms of hearing loss the incidence of the mutation may be far greater.

• To determine whether a hearing defect in a child is hereditary.

• Evaluation of progressive hearing loss in adults.

• To determine the genetic basis for hearing loss in an affected individual, in order to modify therapy.

• To evaluate the risk of having a child with hearing loss.

• Individuals at risk who wish prenatal diagnosis.

• PCR amplification and DNA sequencing of the entire coding region of the Connexin 26 gene.

• Detection of a 342kb deletion involving the Connexin 30 gene.

• PCR amplification of the mitochondrial DNA followed by mutation specific restriction enzyme digestion for mtA1555G mutation.

• Blood EDTA (purple top) tubes:  

            Newborn: minimum 1-2 mL          

            Child/Adult: prefer 2 tubes of 3-5 mL

• Prenatal testing: Please contact the laboratory for instructions.

TURNAROUND TIME:     3 weeks

CPT CODES: