Transcript Hearing Loss & Genetics

Hearing Loss & Genetics:
Understanding the Basics
Anna Frangulov, B.S. Research Coordinator
Children’s Hospital Boston
Why Hearing Loss is
So Common?
Structure of the Ear
Inside the Cochlea “snail”
Sound wave
Hair Cells
Nerve
Structure of the Ear
Conductive HL
Sensorineural HL
What Causes Hearing Loss?
Non-Genetic
• Infections
• Drug-Related
• Traumas/
Exposures
• Structural
Genetic
• Unknown
How Genetic HL occurs?
Chromosomes in Nucleus
23 Pairs of Chromosomes
MOM
DAD
One Chromosome Pair
Genes
“instruction manual”
Genes
Chromosome Pair
Genes
Mutation
“error”
How Is Mutation Inherited?
 Dominant ~15%
 Recessive ~80%
 X-Linked ~2%
 Mitochondrial >2%
Dominant Inheritance
Mutation
“error"
Carrier
Mutation
“error"
How a Recessive Mutation is
Passed?
Carrier –No Hearing Loss
Affected Child—
Hearing Loss
Carrier –No Hearing Loss
Recessive Inheritance
90% of all children w/HL
have normal hearing parents!
Dominant Inheritance
Recessive Inheritance
Parent w/o HL
Parent w/HL
Parent w/o HL
Child w/HL
If a parent has a dominant
mutation, EACH of their children
has a 50% chance of having
hearing loss
Child w/ HL
If two parents have a recessive
mutation, EACH of their children
has a 25% chance of having
hearing loss
HOW? WHO? WHY?
HOW
Do We Know If HL is Genetic?
WHO
Should Have a Genetic Test?
Everybody with Sensorineural HL
Also 2 Mutations in
Cx26!!

Case A: Syphilis

Case B: CMV

Case C: Prematurity

Case D: High bilirubin level
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
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
Things to Consider
1. Talk to knowledgeable professional
 Primary Care/ Pediatrician
 Clinical Geneticist
 ENT
 Genetic Counselor
 Audiologist
 Clinical Molecular Geneticist
Things to Consider
2. What tests are done?
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3. Cost
Cx26
Cx30
Mitochondrial Tests
Pendred
UNDERSTANDING
TEST RESULTS
(example Cx26)
What Does the Result Mean?
 Two Mutations are Found
~18%
 Mutations w/Unknown
 No Mutations are Found
~70%
 One Mutation is Found
Significance
??
~1%
~10%
One Mutation Found
 Mutation unrelated to deafness
 Test did not find 2nd mutation
 Dominant mutation
 There may be a mutation in another gene
Future in Genetics and HL
 More Genetic Tests
GeneChip Technology
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
Educational Material
http://hearing.harvard.edu
Now also in Spanish!
Helpful Information
 Genetic Counselor - Rebecca Madore call 617-335-4534
to set an appointment or email [email protected]
 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 [email protected]