CGC Genetic Risk Assessment & Counseling 2

Question 1

A woman's brother has cystic fibrosis (autosomal recessive), and she is unaffected. Before any testing, what is her risk of being a carrier?

Accepted Answer

2/3

Answer

Of the unaffected offspring of two carriers, two of three expected genotypes are carriers, giving a 2/3 risk.

Question 2

A woman has a 1/2 prior risk of carrying an X-linked recessive condition and has two unaffected sons. What is her posterior carrier risk by Bayesian analysis?

Accepted Answer

1/5

Answer

Joint carrier probability 1/8 divided by (1/8 + 1/2) equals 1/5.

Question 3

A Caucasian individual (prior carrier risk about 1/25) tests negative on a CF panel with a 90% detection rate. What is the approximate residual carrier risk?

Accepted Answer

1/241

Answer

(1/25 x 0.10) / [(1/25 x 0.10) + (24/25 x 1)] is about 1/241.

Question 4

A variant has a relative risk of 2.0 for a disease with a 12% baseline lifetime risk. What is the approximate absolute lifetime risk for a variant carrier?

Accepted Answer

24%

Answer

Multiplying the baseline risk by the relative risk gives about 24%.

Question 5

Which lifetime breast cancer risk estimate generally triggers consideration of annual breast MRI screening in addition to mammography?

Accepted Answer

20% or greater

Answer

ACS and NCCN guidelines recommend supplemental MRI when model-estimated lifetime risk is 20% or higher.

CGC - Certified Genetic Counselor Practice Test

CGC - Certified Genetic Counselor Practice Test

CGC Genetic Risk Assessment & Counseling 2