1. Hearing Loss & Genetics:
Understanding the Basics
Anna Frangulov, B.S. Research Coordinator
Children’s Hospital Boston

2. Why Hearing Loss is So Common?

3. Structure of the Ear

4. Inside the Cochlea “snail”
Sound wave
Hair Cells
Nerve

5. Structure of the Ear
Conductive HL
Sensorineural HL

6. What Causes Hearing Loss?
Non-Genetic
Infections
Drug-Related
Traumas/
Exposures
Structural
Genetic
Unknown

7. How Genetic HL occurs?

8. Chromosomes in Nucleus
23 Pairs of Chromosomes
MOM
DAD

9. One Chromosome Pair
Genes
“instruction manual”

10. Genes

11. Chromosome Pair
Genes
Mutation
“error”

12. How Is Mutation Inherited?
Dominant ~15%
Recessive ~80%
X-Linked ~2%
Mitochondrial >2%

13. Dominant Inheritance
Mutation
“error"

14. Carrier
Mutation
“error"

15. How a Recessive Mutation is Passed?
Carrier –No Hearing Loss
Carrier –No Hearing Loss
Affected Child—
Hearing Loss

16. Recessive Inheritance

17. have normal hearing parents! 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
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

18. HOW? WHO? WHY?

19. HOW Do We Know If HL is Genetic?

21. 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!!

22. 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

23. 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

24. Things to Consider Talk to knowledgeable professional
Primary Care/ Pediatrician
ENT
Audiologist
Clinical Geneticist
Genetic Counselor
Clinical Molecular Geneticist

25. Things to Consider 2. What tests are done? 3. Cost Cx26 Cx30
Mitochondrial Tests
Pendred
3. Cost

26. UNDERSTANDING TEST RESULTS (example Cx26)

27. What Does the Result Mean?
Two Mutations are Found
No Mutations are Found
~18%
~70%
Mutations w/Unknown Significance
One Mutation is Found
~10%
~1% ??

28. One Mutation Found Mutation unrelated to deafness
Test did not find 2nd mutation
Dominant mutation
There may be a mutation in another gene

29. Future in Genetics and HL
More Genetic Tests
GeneChip Technology

30. 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

31. Educational Material
Now also in Spanish!

32. Helpful Information
Genetic Counselor - Rebecca Madore call to set an appointment or
Department of Clinical Genetics – To make appointment with Clinical Geneticist call
National Society of Genetic Counselors (NSGC)
Research Study Participation & Booklets Orders:
Anna Frangulov or