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

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AR Sensorineural Hearing Loss (DFNB1/Connexin 26)

Introduction[edit]

  • 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

Complete Medical History[edit]

Complete Family History and Pedigree[edit]

Prevalence[edit]

  • 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[edit]

  • 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[edit]

  • 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[edit]

  • 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[edit]

  • 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[edit]

  • 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[edit]

  • 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[edit]

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

Notes[edit]

The information in this outline was last updated in 2002.