Genetics

Question 1

What are the 2 universal principles of human genetics?

Answer 1

1) There are no perfect human specimens as we all carry a significant number of DNA glitches
2) Virtually all diseases, except trauma, have a genetic component.

Question 2

What is the WHO-ICF model?

World Health Organizations International Classification of Functioning, Disability, and Health

Answer 2

• Biopsychosocial model that serves as a common language for clinicians and researchers
• Gives us a way to think about the impact of a disease and the individual’s day-to-day function

Question 3

How has our current understanding of genetics found its way into the audiology clinic?

Answer 3

• Inheritance of hearing loss
• Research on genetics and human genome project resulting in identification of genes responsible for hearing loss
• Implementation of universal newborn hearing screenings resulting in earlier identification and diagnosis of hearing loss and more referrals to audiology and genetics

Question 4

What does knowledge of hereditary hearing loss add to the audiologist’s approach in how they diagnose, treat, and manage their patients?

Answer 4

• Monitoring the hearing loss throughout child’s life and knowing what to expect (i.e. should remain stable, may progress, or may be delayed in onset)
• Counseling parents on what to expect regarding hearing one a diagnosis has been made by doctor
• Knowing what to expect in terms of hearing as well as other features associated with various inherited hearing losses (syndromic and nonsyndromic in nature)
• Making appropriate referrals to other professionals such as ophthlamology, cardiology, otolaryngology, SLP, and early intervention for further evaluation

Question 5

What are the two causes of congenital hearing loss?

Answer 5

1) Environmental (~50%)

2) Hereditary (~50%)

Question 6

How is hereditary hearing loss classified?

Answer 6

1) Nonsyndromic (70%)

2) Syndromic (30%)

Question 7

Approximately what percentage of nonsyndromic hearing loss is autosomal dominant?

Answer 7

15-20%

Question 8

What is an autosomal dominant pattern of inheritance?

Answer 8

• Requires only 1 mutated allele to display the disease
• At least 1 parent must have the disease
• Males and females are equally affected

Question 9

What is the chance of passing on an autosomal dominant disease?

Answer 9

• If one parent has the disease, then there is a 50% chance that each of their children will inherit the disease

If both parents have the disease, then there is a 75% chance for each child to inherit the disease

Question 10

Approximately what percentage of nonsyndromic hearing loss is autosomal recessive?

Answer 10

About 80%

MOST COMMON PATTERN OF INHERITANCE

Question 11

What is an autosomal recessive pattern of inheritance?

Answer 11

• Involves heterozygous parents who do not have the disease but are carriers of the disease
• Both parents must be carriers for the disease to be passed down
• Males and females are equally affected

Question 12

What is the chance of passing on an autosomal recessive disease?

Answer 12

25% chance of inheritance with each child

Question 13

Approximately what percentage of nonsyndromic hearing loss is X-linked?

Answer 13

1-2%

Question 14

What is an X-linked pattern of inheritance?

Answer 14

• A disease that is passed down from mother through the X chromosome.
• More common in males than females because they get their X chromosome from mom and need one affected allele to have the disease
• Females need both affected alleles to have the disease

Question 15

Approximately what percentage of nonsyndromic hearing loss is mitochondrial?

Answer 15

<1%

Question 16

What is a mitochondrial pattern of inheritance?

Answer 16

• A mutation in the mitochondria that is passed down from the mom to her children
• Males and females are equally affected

Question 17

What are some of the ethical considerations raised by this area of personalized medicine?

Answer 17

• Not all patients/families have access to genetic testing (expensive)
• Deaf community might not want to be tested because they want to preserve Deaf Community
• Confidentiality–> Should other family members be told about the disease if there is a chance that they too might be affected?

Question 18

How might genetics evolve in the future?

Answer 18

• The discovery of more genes responsible for hearing loss
• Atoh1 gene therapy for hair cell regeneration (Izumikawa et al., 2005)
• Gene therapy for ototoprotection with ototoxic medications (Kawamoto et al., 2004)