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

[1]

• National Association of the Deaf

814 Thayer

Silver Spring, MD 20910

Phone: 301-587-1788

Fax: 305-587-1791

Email: NADinfo@nad.org

[2]

References

• Geneclinics: Nonsyndromic Hearing Loss and Deafness, DFNB1
• National Information Center on Deafness
• Clinical Genetics Lecture

Notes

The information in this outline was last updated in 2002.