Hereditary Hearing Loss Panel

Connexin Hearing Loss Panel: Cx26 and Cx30 Gene Analysis :

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 is genetic with over 30 autosomal recessive (70-80%), dominant (23-30%) and X-linked (2-3%) forms. A large proportion (60-75%) of nonsyndromic hearing loss in children 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. Consequently, affected patients in which only a single Cx26 mutation, is detected should also undergo testing for the Cx30 mutation. Additionally, testing may be combined with testing for mitochondrial hearing loss in a Nonsyndromic Hearing Loss Panel for the most efficient and economical diagnosis available.

REASONS FOR REFERRAL:

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

TESTING METHODOLOGY:

PCR amplification of the region including the G380R mutation, followed by mutation specific restriction enzyme digestion; 99% detection of the G380R mutation.

SPECIMEN REQUIREMENTS:

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.

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

TURNAROUND TIME: 3 weeks

CPT CODES: