Genetic Counselling and Risk Assessment

Question 1

Describe autosomal dominant inheritance
-what are 3 examples

Describe autosomal recessive inheritance
-what are 2 examples

Answer 1

Children of an affected parent => 50% chance of being affected themselves
=> Males and females affected equally

HD
HBOC
Marfans

Children of 2 carrier parents => 25% chance of being affected
=> Males and females affected equally

CF
Sickle cell anemia

Question 2

Describe X linked dominant inheritance

Describe X linked recessive inheritance

Answer 2

Affected mother => 
-daughters - 50% affected
-sons - 50% affected
Affected father =>
-daughters - 100% affected
-sons - 0% affected

Affected mother =>
-daughters - 100% carrier
-sons - 100% affected
Carrier mother =>
-daughters - 50% carrier
-sons - 50% affected
Affected father =>
-daughters - 100% carrier
-sons - 0% affected

Question 3

Describe Y linked inheritance

Answer 3

Affected father =>

• daughters - 0% affected
• sons - 100% affected

Question 4

Describe mitochondrial inheritance

Answer 4

Female transmission only

-effect dependent on % of mitochondrial affected

Question 5

Difference between penetrance vs expressivity

Answer 5

Penetrance - proportion of individuals carrying variant that also expresses associated trait

Expressivity - variation in expression of trait

Question 6

Describe HD in relation to genetic testing

Answer 6

100% penetrant
-patients have a 10 year prognosis from first symptoms

Do not test children as symptoms do not arise in childhood

2 consultations needed with genetic counsellor before testing

2 possible thoughts

• if I know I have it, I can prepare
• if I know I have it, I won’t cope

Question 7

Describe hypertrophic cardiomyopathy

Answer 7

Can test children under 18 as symptoms present in childhood

25% penetrance

Patients normally have diagnosis so results do not impact on QOL or treatment
Can support asymptomatic family members

Question 8

What are the factors that suggest an inherited predisposition

Answer 8

Common cancer in unusually young age

Uncommon cancer in 2+ close relatives

Multiple primary tumours
Bilateral tumours

Associated abnormalities

• polyps
• skin findings

Question 9

What is the difference between familial and hereditary cancer

Answer 9

Familial - generally not eligible for testing

• environmental factors
• chance
• undiscovered gene mutation

Hereditary

• caused by inherited gene mutation that puts them at increased risk for cancer
• Autosomal dominant pattern = Lynch syndrome (hereditary non polyposis colorectal cancer/HNPCC) from MMR
• Autosomal dominant pattern = HBOC from BRCA1,2

Question 10

What are the reproductive options for people with mutated genes

Answer 10

Natural birth

Prenatal screening
-miscarriage
-potential need for termination
Surrogacy/adoption

Preimplantation Genetic Diagnosis
-genetic analysis of 1 cell from an 8 cell embryo alongside IVF to improve chances of normal pregnancy

Question 11

What is the difference between absolute risk and relative risk

How can you frame risk in a more positive light?

Answer 11

Absolute risk - likelihood of an event happening under specific conditions

Relative risk - likelihood of an event happening compared to another group with different characteristics

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