Handbook of Genetic Counseling/AR Sensorineural Hearing Loss (DFNB1/Connexin 26)

AR Sensorineural Hearing Loss (DFNB1/Connexin 26)

Introduction

 * Acknowledge prior phone contact
 * What information have you been given already?
 * Have you done any research on your own? What have you found out?
 * What concerns or questions would you like to have answered today?
 * Outline session

Prevalence

 * DFNB1 accounts for 50% of AR sensorineural hearing loss
 * Prevalence is ~14/100,000
 * 1/2000 congenital hearing impairment
 * 70% of these are nonsyndromic
 * 80% of nonsyndromic hearing loss is AR
 * 50% of these are due to GJB2 mutation
 * 1/30 people in general population are carriers

Genetics

 * Gene: GJB2
 * Chromosome location: 13q11-12
 * Protein: Connexin 26
 * Gap junction protein
 * Involved in conducing signal to the brain
 * Autosomal recessive inheritance
 * 25% risk of hearing loss for future children
 * 50% risk of being a carrier for the mutation
 * 25% risk of being an unaffected noncarrier

Molecular Testing

 * Detects 95% of disease-causing mutations
 * ~66% of mutations - 35delG
 * ~30% of mutations - other GJB2 mutations
 * ~4% mutations - unknown
 * carrier testing is available and can be offered to at-risk family members
 * prenatal testing is available but rarely pursued

Clinical Features

 * nonprogressive sensorineural hearing impairment
 * severe to severe-profound hearing loss
 * diagnosed by Auditory Brainstem Response or pure tone audiometry and presence of no related anomalies
 * no other associated health problems
 * no balance problems

Management

 * When diagnosis is known or suspected
 * Assessment of auditory acuity by ABR or pure tone audiometry
 * Fitting with hearing aids
 * Early intervention
 * Follow-up care
 * semiannual examination by physician familiar with hereditary hearing impairment
 * repeat pure tone audiometry to confirm stability of loss
 * consideration for cochlear implants

Psychosocial Issues

 * Deaf child born to hearing parents
 * How did you feel when you first found out?
 * How have your feelings changed?
 * How have other family members reacted?
 * Have you been in contact with any other families?
 * Have you been in contact with any support groups?

Resources

 * American Society for Deaf Children
 * PO Box 3355
 * Gettysburg, PA 17325
 * Phone: 717-334-7922
 * Fax: 717-334-8808
 * Email: ASDC1@aol.com
 * 


 * National Association of the Deaf
 * 814 Thayer
 * Silver Spring, MD 20910
 * Phone: 301-587-1788
 * Fax: 305-587-1791
 * Email: NADinfo@nad.org
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