Hearing Loss & Genetics

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Hearing Loss Genetics

• Understanding the Basics
• Anna Frangulov, B.S. Research Coordinator
• Childrens Hospital Boston

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Why Hearing Loss is So Common?
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Structure of the Ear
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Inside the Cochlea snail
Hair Cells
Nerve
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Structure of the Ear
Sensorineural HL
Conductive HL
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What Causes Hearing Loss?

• Infections

Non-Genetic

• Drug-Related

• Traumas/
• Exposures

• Structural

Genetic

• Unknown

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How Genetic HL occurs?
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Chromosomes in Nucleus
23 Pairs of Chromosomes
MOM
DAD
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One Chromosome Pair
Genes instruction manual
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Genes
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Chromosome Pair
Genes
Mutation error
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How Is Mutation Inherited?

• Dominant 15
• Recessive 80
• X-Linked 2
• Mitochondrial gt2

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Dominant Inheritance
Mutation error"
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Carrier
Mutation error"
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How a Recessive Mutation is Passed?
Carrier No Hearing Loss
Carrier No Hearing Loss
Affected Child Hearing Loss
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Recessive Inheritance
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90 of all children w/HL have normal hearing
parents!
Recessive Inheritance
Dominant Inheritance

Parent w/o HL
Parent w/HL
Parent w/o HL
Child w/HL
Child w/ HL
If a parent has a dominant mutation, EACH of
their children has a 50 chance of having
hearing loss
If two parents have a recessive mutation, EACH of
their children has a 25 chance of having
hearing loss
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HOW? WHO? WHY?
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HOW Do We Know If HL is Genetic?
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(No Transcript)
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WHO Should Have a Genetic Test?
Everybody with Sensorineural HL

• Case A Syphilis
• Case B CMV
• Case C Prematurity
• Case D High bilirubin level

Also 2 Mutations in Cx26!!
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WHY Should We Have a Genetic Test??

• Benefits for Genetic Testing
• a definite cause
• family members realize that they are carriers
  determine risk factors for future children
• helps to find appropriate treatment/ management

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• Limitations for Genetic Testing
• does not necessarily find the answer
• severity of HL may not be predicted
• a person may have mutations, but not have HL

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Things to Consider

• Talk to knowledgeable professional

• Primary Care/ Pediatrician
• ENT
• Audiologist

• Clinical Geneticist
• Genetic Counselor
• Clinical Molecular Geneticist

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Things to Consider

• 2. What tests are done?
• Cx26
• Cx30
• Mitochondrial Tests
• Pendred
• 3. Cost

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UNDERSTANDING TEST RESULTS(example Cx26)
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What Does the Result Mean?

• Two Mutations are Found

• No Mutations are Found

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70

• One Mutation is Found

• Mutations w/Unknown Significance

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1
??
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One Mutation Found

• Mutation unrelated to deafness
• Test did not find 2nd mutation
• Dominant mutation
• There may be a mutation in another gene

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Future in Genetics and HL

• More Genetic Tests

GeneChip Technology
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Research Studies

• Connexin 26 Study- individuals with Cx26
  mutations
• Genetic Testing and Counseling Study - If you or
  your child has had genetic testing for hearing
  loss and you are willing to fill out a
  questionnaire
• GeneChip Study - individuals with hearing loss
  who and parents with normal hearing
• Novel Gene Discovery Study - five or more family
  members with hearing loss

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Educational Material
http//hearing.harvard.edu
Now also in Spanish!
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Helpful Information

• Genetic Counselor - Rebecca Madore call
  617-335-4534 to set an appointment or email
  rmadore_at_partners.org
• Department of Clinical Genetics To make
  appointment with Clinical Geneticist call
  617-355-6394.
• National Society of Genetic Counselors (NSGC)
  www.nsgc.org
• Research Study Participation Booklets Orders
• Anna Frangulov
• 617-515-2962 or anna.frangulov_at_childrens.harva
  rd.edu