(SOLVED) Your patient has had genetic testing for mutations in genes that commonly cause inherited breast cancer

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Academic Level: Undergrad. (yrs 1-2)

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Question

1.Your patient has had genetic testing for mutations in genes that commonly cause inherited breast cancer. Her test results come back “variant of unknown significance.” Explain these results and what you would suggest regarding her need for breast cancer screening.

2. Describe a situation in which cytogenetic testing might be ordered. How would this be different from testing for single-gene problems?

3. Discuss a situation in which prenatal cell-free DNA (cf DNA) screening may be appropriate. Discuss the possible pros and cons of the procedure.

4. Distinguish between predispositional and presymptomatic genetic testing. Provide an example of a situation when each would be used.

Expert solution paper

Your patient has had genetic testing for mutations in genes that commonly cause inherited breast cancer. Her test results come back “variant of unknown significance.” Explain these results and what you would suggest regarding her need for breast cancer screening.

This means that the test found a gene change (variant), but it’s not known if this particular change affects your risk.

2. Describe a situation in which cytogenetic testing might be ordered. How would this be different from testing for single-gene problems?

Cytogenetic testing is the examination of chromosomes to determine chromosomal abnormalities such as aneuploidy and structural abnormalities. Cytogenetic testing can be performed in a variety of situations, including solid organ malignancies, hematologic malignancies, congenital diseases. It can be performed prenatally after biochemical screening or ultrasound with abnormal findings. It is also used for parents with multiple miscarriages or significant findings in their pedigree analysis. Postnatally, cytogenetic testing plays a role in distinguishing patients with mosaicism, intellectual disability, autism, or developmental delays.

Single gene problem: Single gene tests look for changes in only one gene. Single gene testing is done when your doctor believes you or your child have symptoms of a specific condition or syndrome. Some examples of this are Duchene muscular dystrophy or sickle cell disease.

3. Discuss a situation in which prenatal cell-free DNA (cf DNA) screening may be appropriate. Discuss the possible pros and cons of the procedure.

cell-free DNA (cfDNA), also called non-invasive prenatal screening or non-invasive prenatal testing (NIPT), screens for risk of conditions like trisomy 21, trisomy 18, trisomy 13 and sex chromosome conditions as early as 10 weeks

circulating tumor DNA (ctDNA) - originating from the tumor cells, consists of a small fraction of the cfDNA

It is found in the body fluids, such as, blood, urine, saliva, cerebrospinal fluid, and breast milk as DNA fragments. They are present in the circulation, representing the remnants of tumor, and hence can act as cancer biomarkers. Studies have indicated high level of cfDNA in the plasma of cancer patients compared to the healthy control (Temilola et al.).

Pros

Cons

Time to process FFPE samples is more

Blood draw is easier as compared to multiple biopsies
Sample size for tissue is limited
Preservation is easier
Helps to monitor serial progression of disease
Provides real-time picture of the disease- the half-life of cfDNA in the circulation is 16 mins-2.5 hr (Chen and Zhao)
Representative of tumour heterogeneity
Helps to assess the risk of relapse in the patients

Sensitivity is low compared to tissue biopsy
Detects mutation from hematopoietic clones instead of the actual tumor
Proper clinical guidelines are not yet established
Possibility of false positives- detection of cancer, when in reality it is not present (“Biopsy: Using DNA in Blood to Detect, Track, and Treat Cancer”)
May be misleading in making decisions- the release of cfDNA is representative of whole or part of the tumour
Distinguishing between carrier and passenger mutation of cfDNA is difficult

4. Distinguish between predispositional and presymptomatic genetic testing. Provide an example of a situation when each would be used.

Predictive testing is used to clarify the genetic status and history (genealogy) of an asymptomatic family member at risk for a genetic disorder. A basic condition for the use of predictive testing is the identification of specific disease mutation(s) in an affected family member. Predictive testing can be divided into two different types presymptomatic and predispositional.

Presymptomatic gene testing: Presymptomatic testing (PST) is the performance of a genetic test on an asymptomatic individual at risk of a condition to determine whether the person has inherited the disease-causing mutation.

Example : Huntington disease

Predisposition testing: Predisposition testing (i.e., genetic testing that provides information about a person's susceptibility to disease) is now available for several inherited forms of cancer. There are a range of conditions and illnesses linked to a genetic predisposition. These include certain cancers, diabetes, obesity, heart disease, asthma, celiac disease, and more.

Example: Genetic testing of the BRCA1 gene for breast and ovarian cancer susceptibility is the most common example of predispositional testing; the findings of a particular genomic variant predispose the occurrence of the breast cancer. It is worth noting that predispositional testing does not indicate a 100% risk of developing the condition. It differs essentially from presymptomatic testing as it informs individuals about the risk developing the condition; however, the degree of certainty is unknown⁸ (US National Library of Medicine).