Genetic epidemiology of cancer and studies of familial cancers Flashcards Preview

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Flashcards in Genetic epidemiology of cancer and studies of familial cancers Deck (15):

Why do we want to identify inherited cancer genes?

  1. Gsin an understanding of disease mechanism
  2. Help identify targets for therapy
  3. Identify risk populations
  4. Identify people that might respond best to particular drugs (pharmacogenetics)
  5. Identify why people might react badly to drugs


How are LOH detected 

Microsatellite markers when blood and tumour DNA samples are compared


Why are familial cancer carriers more likely to develop cancer 

Because the first "hit" in the tumour suppressor gene has been inherited and is present in all the cells in their body. Only requires the second hit (often loss of a larger chromosomal region including the WT allele on the other chromosome) 


How have familial cancers been identified

Positional cloning - linkage analysis followed by cloning and sequencing 

Identification of deletions and LOH in tumours 

Testing tumours for mutations of genesknown to be involved in cell cycle regulation

Recently, sequencing of candidate genes in people with a family history of cancer. 


What are examples of the rare cancer syndromes and give examples of germline mutations. 

Retinoblastoma, APC

>1000 relative risk, 

mutations in Rb1 and APC. 


What are examples of familial forms of common cancers 

10 - 100 relative risk


Breast and colon cancer.

Mutations in BRCA1/2, MSH2/1 etc


What is the process for positional cloning 

Assemble some families with many affected individuals

Genotype their DNA using microsatellite markers that span the whole genome

Look to see if the disease co-segregates with markers on a particular chromosome (done by linkage analysis)

Identify likely candidate genes in the region of interest and look for mutations carried by people with the disease but not by healthy family members. 


What are characteristics of familial breast cancer 

Early age of onset

Breast and ovarian cancer in the same familiy

bilateral disease is frequent (both breasts effected)

Males in the family are also effected. 


What is linkage analysis 

Genotype markers and observe whether or not particular marker alleles segregate with disease in families in which there are multiple cases.

We can use these data to work out the likelihood our marker is linked to the disease. 

The answer is in the form of lod score which is a measure of the likeliness that the disease and the marker are linked. 


What did linkage analysis of familial breast cancer reveal.

lod score of 5.98 in early onset at marker D17S74 at chromosome 17q21

chromosome 17 is linked to breast cancer


What is genetic heterogeneity?

Multiple genes are responsible for causing the disease in question



What is the role of the BRCA2/1 genes in DNA repair

ATM phosphorylates MRE11 and NBS1 in response to DNA damage

The RAD50, NRE11, NBS1 complex binds at sites of DNA double strand breaks and initiates DNA repair

Mutations in these genes cause familial syndroms with genomic instability. 


What are the common features of NBS and AT mutants 

Cells show increased sensitivity to ionising radiation 

Fail to induce p53 at the G1/S checkpoint.

Fail to stop DNA synthesis in response to ionising radiation. 

Phenotype is one of failing to signal DNA damage, 


What is the role of BRCA1 with the MRE11/RAD50/NBS1 complex pathway

BRCA1 also associates with the complex

ATM phosphorylates BRCA1

AT mutant cells are unable to phosphorylate BRCA1

Mutated BRCA1 lacking two phosphorylation sites is unable to rescue the radiation hypersensitivity of a BRCA1 deficient cell line.

This pathway is important to protect cells against DNA damage


Draw out the pathway of BRCA1 and its relationship with other complexes/ATM