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Life Protection > Cancer genetics > Flashcards

Cancer genetics Flashcards

1
Q

What are Mendelian diseases?

A

= monogenic

Disease caused by mutation in a single gene, with little or no impact from the environment

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2
Q

What are Oligogenic diseases?

A

= polygenic

Disease caused by combined effects of a few genes (oligogenic) or many different genes (polygenic)
Each gene contributes only a small proportion to total disease risk

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3
Q

What are multifactorial diseases?

A

= polygenic + environmental factors

disease or traits resulting from multiple risk genes and their interplay with the environmental stimuli

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4
Q

What are the different types of mendelian inheritance patterns?

A

(usually in monogenic disorders)

autosomal recessive
autosomal dominant
X-linked recessive
X-linked dominant (rare)
Y-linked (v. rare)
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5
Q

What are examples of autosomal recessive disorders?

A
  • cystic fibrosis
  • sickle cell anaemia
  • spinal muscular atrophy
  • phenylketonuria
  • Tay Sachs disease
  • Meckel-Gruber syndrome
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6
Q

What are examples of autosomal dominant disorders?

A
  • Achondroplasia
  • Huntington’s
  • Marfan syndrome
  • polycystic kidney disease
  • polydactyly
  • familial hypercholesterolaemia
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7
Q

How do X-linked recessive disorders present for inheritance?

A
  • only males affected
  • Females are carriers (as they inherit functional allele from X-chr from mother)
  • there is no male to male transmission
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8
Q

What are examples of X-linked recessive disorders?

A
  • red green colour blindness
  • Duchenne muscular dystrophy
  • Haemophiia A and B
  • X-linked ichthyosis
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9
Q

What are examples of X-linked dominant disorders?

A
  • cranio-fronto-nasal dysplasia

- hypophosphaaemic rickets

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10
Q

Where is mitochondrial DNA inherited from?

A

mother (in the egg)

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11
Q

What is penetrance?

A

the percentage of individuals who exhibit a particular phenotype for that genotype
[in a given generation/population]

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12
Q

What is phenotype expression/expressivity?

A

for a given genotype, what is the degree to which the phenotype is expressed?
e.g. how severe in the phenotype between different individuals with the same genotype

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13
Q

What are the different types of penetrance?

A
  • COMPLETE
    everybody in that family with the mutation will show clinical signs
  • INCOMPLETE (reduced)
  • LOW
    <20% of family members with the mutation show clinical signs
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14
Q

What is mosaicism?

A

when not all the cells in the body harbours the genetic defect

caused by a post-zygotic mutational event

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15
Q

What are the 2 cellular hallmarks of cancer?

A
  • apoptosis malfunction
  • uncontrolled cell growth

facilitated by accumulation of DNA mutations in cells

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16
Q

Which genes are responsible for controlling cell growth (and often mutated in cancer)?

A
  • oncogenes
  • tumour suppressor genes
  • DNA repair genes
  • Apoptosis genes
17
Q

What kind of cancer arises from post zygotic mutations?

A 
usually sporadic (rather than familial)
similar to de novo somatic mutations
18
Q

What is the two-hit theory of cancer causation?

A

inheritance of a gremlin mutation becomes a risk factor for cancer

It then reduces the number of further post-zygotic mutations required to cause cancer

19
Q

What is the nature of cancer caused by inherited/family history?

A

usually

  • early age at onset <50
  • more than one relative with the same type of cancer
  • clustering of certain cancer types
  • family member with multiple cancers
  • bilateral tumours
  • genetic testing usually beneficial
20
Q

Why does familial cancer have an earlier onset?

A

inherited genetic risk increases overall cancer risk and lowers threshold for additional mutations in the genome

21
Q

What proportion of all cancer are sporadic? What mutations cause this?

A

90% of all cancers

post-zygotic mutations

22
Q

What proportion of all cancer are hereditary? What mutations cause this?

A

10% of all cancer

germline mutations
+post-zygotic combos

23
Q

What factors indicate an increased likelihood of having familial cancer?

A
  • cancer in 2 or moe close relatives
  • early age at Dx
  • multiple and different types of tumours in one person
  • male breast cancer
  • ethnicity with known increased risk
24
Q

Which genes are implicated in the hereditary breast-ovarian cancer syndrome?

A

BRCA1

BRCA2

25
Q

Which gene is implicated in retinoblastoma?

A

RB1

26
Q

Which gene is implicated in Cowden’s syndrome?

A

PTEN

27
Q

Which gene is implicated in Lynch syndrome?

A

MSH2

MLH1

28
Q

Of the BRCA genes, which confers a higher risk for ovarian cancer?

A

BRCA1 > BRCA2

29
Q

What is the BRCA1-related familial breast/ovarian cancer syndrome an example of?

A

autosomal dominant inheritance
with high penetrance

lifetime cancer risk increased by 30-70%

30
Q

Are family cancers always completely penetrant?

A

nope
Can show reduced penetrance
e.g with BRCA1 mutations
unaffected mum with risk genotype may have affected son

31
Q

How may expressivity affect phenotypes for cancer mutations?

A

may affect:
- age of onset
- type of cancer
may vary person-person even within same family

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