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Genetics > M3 L17: Genetic counseling, human genetics, and cancer genetics > Flashcards

M3 L17: Genetic counseling, human genetics, and cancer genetics Flashcards

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1
Q

why does medical genetics involve the patient’s family more than other medical fields

A

1) family plays a role in patient’s care

2) patients’ diagnosis could have implications for the family since genetic diseases are heritable

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2
Q

genetic diseases caused by mut in single genes

A

1) huntingtons
2) PKU

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3
Q

genetic diseases caused by muts in one of many genes (genetic heterogeneity)

A

fanconi anemia (LOF mutation in one of 3 genes)

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4
Q

example of a genetic disease influenced by the environment

A

PKU

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5
Q

what are 4 types of hereditary diseases

A

1) mendelian
2) mitochondrial
3) chromosomal
4) multi-factorial

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6
Q

how are mendelian conditions inherited

A

mut in single gene

dom/rec

can be autosomal or X linked

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7
Q

how are mitochondrial muts inherited

A

mut in single gene but inherited maternally

variable penetrance/expressivity

usually more severe in males

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8
Q

how are chromosomal muts inherited

A

add extra copy

usually spontaneous not inherited

influenced by maternal age

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9
Q

how are multi factorial conditions inherited

A

inherit increased susceptibility for heart disease, cancer

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10
Q

what is presymptomatic testing and a disease it’s used for

A

genotype adults before onset of symptoms

common for huntingtons

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11
Q

challenges with presymptomatic testing and huntingtons

A

can help plan for future but traumatic if diagnosis is positive

ethical issues because diagnosis can indicate others are at risk for developing the disease too

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12
Q

what are the two types of fetal screening

A

non invasive (no threat to fetus)

invasive (some risk to fetus)

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13
Q

examples of non invasive fetal screens

A

1) maternal serum sampling: test blood and measure AFP, uE3, HCG (screening not diagnostic)

2) fetal cell sorting: draw mother’s blood and separate fetal cells –> extract fetal DNA (hard bc fragile and 1 billionth of the cells)

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14
Q

examples of invasive fetal screens

A

1) amniocentesis: use needle to extract amniotic fluid and fetal cells

2) chronic villus sampling: pass tube transvaginally to get fetal cells from chorion

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15
Q

what is preimplantation screening? common context?

A

remove a single cell from embryo during 8-16 cell stage –> genotype it

common for IVF

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16
Q

What is the Guthrie test? who developed it

A

robert guthrie developed heel stick to screen for PKU - first widely used genetic screen for newborns

heel has few nerve endings - only use for diseases where QOL significantly improved if genotype is known/can be reliably diagnosed

place newborn blood with bacteria on media with phenylalanine analog (toxic) –> if bacteria grows, it means lots phenylalanine in blood

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17
Q

What causes tay-sachs disease? why do carrier screening?

A

recessive lethal neuromuscular disorder: no functional hexosaminidase –> GM2 ganglioside builds up –> kills nerve cells

1/30 ashkenazi jewish people are carriers –> test to know risk before having kids

very poor QOL for individuals

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18
Q

How can direct to consumer genetic tests be helpful? example?

A

test for genetic variants that are associated with certain phenotypes and increased risk for some conditions

ex) LOF of alpha-1 antitrypsin –> hyperactive protease in lungs and liver –> difficulty breathing/COPD

not a diagnostic test but can help you make informed lifestyle decisions (especially with a genetic counselor)

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19
Q

3 goals of genetic counselor

A

communicate info, discuss options, help patient reach own decision

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20
Q

what are the 4 variables to consider when assessing risk when having children

A

1) inheritance pattern
2) family structure
3) family genotype info
4) pop freq of the allele

21
Q

Why is cancer a disease of the genome?

A

cancer includes several diseases that are all caused by accumulated mutations in somatic cells –> causes cells to divide abnormally/rapidly

22
Q

cancer is the 2nd leading cause of death after _____? Which two cancers cause the most deaths?

A

heart disease

lung and breast

23
Q

what 2 types of muts are hallmarks of cancer and malignant tumors?

A

1) GOF in proto-oncogenes: promote cell cycle progression

2) LOF in tumor supressor genes: normally slow down the cell cycle

24
Q

what is angiogenesis

A

developing new blood vessels

25
Q

what is metastasis

A

cancer cells invading other tissues (local or breaking off –> start new tumor)

26
Q

what are driver and passenger mutations

A

drivers: mutations in cancer cells that lead to cancer progression

passengers: mutations in cancer cells that do not lead to cancer progression

27
Q

what is the biggest risk factor for cancer

A

age

28
Q

is everyone equally susceptible to all sporadic cancers? What is the percentage of development?

A

yes

90%

29
Q

what is familial cancer

A

presence of a germline mutation increases susceptibility to a certain cancer

30
Q

examples of familial cancer

A

chronic myelogenous lukemia

retinoblastoma

li fraumeni syndrome

breast/ovarian

31
Q

mechanism of chronic myelogenous leukemia (CML)

A

reciprical translocation btwn chrom 22 and 9 –> shortened 22 (philadelphia chrom) and fusion of C-ABL and BCR genes –> chimeric gene –> constitutively stimulate growth

BCR normally transfers external growth signals to nucleus

detection of phil chrom essentially diagnostic

causes bone marrow to overproduce granulocytes

32
Q

what is sporadic retinoblastoma

A

both copies RB1 (autosomal gene) get mutated in cell that gives rise to retina

VERY RARE FOR TWO INDEPENDENT MUTATIONS

usually only one tumor in one eye

33
Q

mechanism for retinoblastoma

A

RB1 encodes protein pRB –> normally binds TF E2F, releases on certain cues

mutated pRB can’t bind E2F –> E2F upregulates genes involved in G1/S transition –> cells w/ RB1 muts continuously commit to division –> tumor

34
Q

what is hereditary retinoblastoma

A

zygote heterozygous for RB1 mut –> dev cancer if they get one sporadic mut

one mut more likely to occur than two

usually multiple tumors in both eyes

35
Q

what’s the two hit hypoth? who developed it?

A

alfred knudson

if cancer causing muts occur at some background rate, indiv who are heterozygous for mutations are at a higher risk for cancer than homo WT (only need one sporadic mut to have two hits)

36
Q

what’s li fraumeni syndrome

A

inherited susceptibility to many types of cancer

37
Q

mechanism of li fraumeni syndrome

A

autosomal dominant

mut in TP53 (tumor supressing gene) which encodes p53 “guardian of the genome” (TF that stops cells w/ damaged DNA from dividing via G1 arrest)

nonfxn p53 –> damaged cells replicate and accumulate more muts –> cancer

38
Q

what percentage of breast/ovarian cancers are sporadic?

A

90-95%

39
Q

char of sporadic vs inherited susceptibility breast/ovarian cancers

A

sporadic: avg age onset is 60 yrs, unilateral

familial: onset younger than 60, bilateral, contralateral (one side then other at later time), BCRA1 and 2 muts increase risk (both involved in DNA repair and follow 2 hit hypoth)

40
Q

what is cancer genomics

A

sequence cancer genomes to determine types of muts that lead to disease progression

41
Q

4 key takeaways from cancer genomics

A

no 2 tumors, even of the same type, have the exact same mutations

some mutations common to many types of caner (p53)

specific cancers usually have certain mutations (CML phil chrom and retinoblastoma RB1)

epigenetic irregularities common (muts in chrom mod proteins/DNA methyltransferases)

42
Q

3 main types cancer treatments/pros and cons

A

radiation: can be mutagenic

chemo: targets rapidly dividing cells; side effects; not equally effective for all cancers

surgery: remove tumor; impossible with certain tissue types

43
Q

what is targeted cancer therapy? example?

A

can target mutant proteins with drugs if you know the causal mutation

gleevec targets C-ABL-BCR fusion protein in CML –> stop protein and stop overproduction of granulocytes

44
Q

example of cancer gene therapy

A

CAR-T cells for acute lymphoblastic leukemia

isolate T cells from patient –> modify antigen receptor to bind CD-19 (expressed by cancer cells) –> grow and inject into patient –> CAR-T cells kill cancer cells in blood

also on target off tumor effects: b cells also have CD-19 –> CAR-T cells kill b cells –> body continuously makes more b cells –> stimulates CAR-T cells to divide/stay present

45
Q

Design an assay that would allow for the disease allele of the huntington gene to be identified using PCR.

A

Collect DNA from the patient, do PCR with primers that are complementary to the sequences up and downstream of the Huntington gene, do gel electrophoresis of the amplified patient’s DNA with a WT Huntington gene. If the WT gene travels farther, then the individual likely has the Huntington repeat sequences.

46
Q

Are direct-to-consumer genetic tests diagnostic? Why or why not?

A

No because they can only identify some genetic variants that might increase your risk for developing genetic diseases. They can help you make informed choices, especially going through the results with a genetic counselor.

47
Q

Describe one potential drawback of direct-to-consumer genetic testing in the absence of the support of a genetic counselor.

A

People might interpret the results incorrectly. They might not know what phenotypes the variants can cause, what steps they should take to decrease their risk, and they might worry that they are definitely going to develop a disease if they have a genetic variant. There may be other factors like other genes and environment that influence risk.

47
Q

Cancer can be thought of as natural selection playing out among somatic cells. Explain this idea.

A

Cancer refers to many diseases that have unregulated cell growth and division that impacts normal cell/tissue functioning. Cells that can grow and divide more than others are more successful in terms of fitness and natural selection, but this has negative effects on the patient.

Genetics (19 decks)

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