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Genetics Flashcards

1
Q

Which function do disease associated mutations alter?

A

Protein function

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2
Q

What percentage of breast cancer is hereditary?

A

5-10%

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3
Q

What percentage of ovarian cancer is hereditary?

A

5-10%

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4
Q

Name the two main hereditary causes of colorectal cancer and the percentage of case?

A

Lynch Syndrome/HNPCC: 5%

FAP: 1%

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5
Q

What are clonal expansions?

A

When mutations begin to build up in more than one cell e.g. not just once cell going bad

How tumours work

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6
Q

Name the features of germline mutations

A
  • Inherited from single alteration in egg or sperm
  • All cells in the offspring are affected
  • Are heritable
  • Cause cancer family syndromes
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7
Q

Name the features of somatic mutations

A
  • Occur in nongermline tissues

- Are noninheritable

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8
Q

Where do oncogenes occur in the cell cycle?

A

G1 (cell growth)

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9
Q

Where do tumour suppressor genes and DNA repair genes occur in the cell cycle?

A

S (synthesis)

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10
Q

How many mutations does an oncogene need in order for cancer to develop?

A

One - leads to accelerated cell division

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11
Q

Which oncogene is responsible for leukaemia and where is it found?

A

ABL on the BCR-ABL Fusion Protein

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12
Q

Which cancer is hereditary and normally presents in early childhood?

A

Retinoblastoma - due to tumour suppressor gene mutations

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13
Q

How many mutations do tumour suppressor genes need to lead to cancer?

A

Two - either two mutations or mutation + loss of gene

One - leads to a susceptible carrier

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14
Q

Name a cancer which needs multiple mutations to progress to cancer

A

Colon cancer - each mutation progresses the cancer from hyper-proliferative epithelium to metastasis

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15
Q

Which mutation is the main mechanism for familial cancer?

A

Faulty DNA Mismatch Repair

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16
Q

Name the features of lynch syndrome/ HNPCC

A
  • Mutation in mismatch repair genes
  • Excess of colorectal, endometrial, urinary tract, ovarian and gastric cancers
  • Adenoma: carcinoma sequence for polyp formation
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17
Q

What are the clinical features of HNPCC?

A
  • Early but variable age at CRC diagnosis

- Commonly tumour in proximal colon

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18
Q

List the cancer risks in Lynch syndrome from highest to lowest

A 
Colon
Endometrial
Stomach
Biliary tract
Ovarian
Sebaceous gland
CNS
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19
Q

What are the cancer risks for BRCA1 and 2 in females?

A

Breast cancer: 60-80%
Second Primary Breast Cancer: 40-60%
Ovarian Cancer: 20-50%

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20
Q

What are the risks of the BRCA1 and 2 gene for males?

A

Increased risk of prostate and breast cancer (esp. BRCA2)

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21
Q

Name the features of autosomal dominant inheritance

A
  • Each child has 50% chance of inheriting the mutation
  • No skipped generations
  • Equally transmitted by men and women
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22
Q

What features would make you suspect a hereditary cancer syndrome?

A
  • Cancer in 2 or more close relatives (in same side of family)
  • Early age at diagnosis
  • Multiple primary tumours
  • Bilateral or multiple rare cancers
  • Characteristic pattern of tumours (e.g. breast and ovary)
  • Evidence of autosomal dominant transmission
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23
Q

What is the process of cancer genetics?

A
  • Obtain detailed FH
  • Confirm diagnoses of cancer
  • Risk estimation
  • Counselling
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24
Q

Name the steps in a clinical genetics consultation for cancer

A
  • FH
  • Risk estimation
  • Explanation of basis of risk
  • Interventions (lifestyle, prevention, screening, surgery and awareness)
  • Genetic testing in high risk patients
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25
Q

What are the options for breast surveillance?

A
  • Breast awareness
  • Early clinical surveillance
  • Annual or clinical breast exams
  • Mammography (moderate/high risk)
  • MR screening for highest risk
26
Q

How does a prophylactic mastectomy for BRCA1/2 gene carriers work?

A
  • Removes most but not all breast tissue
  • Significantly reduces breast cancer risk in women with FH
  • Total or subcutaneous mastectomy
  • BRCA1 mutation positive women breast cancer incidence reduced to 5%
27
Q

How does a prophylactic oophorectomy work?

A
  • Eliminates risk of ovarian cancer
  • Peritoneal carcinomatosis may still occur
  • Laparoscopic reduces postsurgical morbidity
  • Induces surgical menopause but HRT till 50 does not chance BRCA risk
  • Risk of subsequent BRCA halved in mutation positive women
28
Q

What are the surveillance options for CRC?

A

Colorectal: colonoscopy
Endometrial: symptom awareness and surgery

29
Q

What are the genetic testing options for lynch syndrome?

A

IHC for mismatch repair gene proteins or micro satellite instability testing (MSI)

Gene screen if IHC/MSI are high

30
Q

What are the benefits of genetic testing?

A
  • Identifies highest risk
  • Identifies non-carrier in families with a known mutation
  • Allows early detection and prevention strategies
  • May relieve anxiety
31
Q

What are the risks and limitations of genetics testing?

A
  • Does not detect all mutations
  • Continued risk of sporadic cancer
  • Efficacy of interventions is variable
  • May result in psychosocial or economic harm
32
Q

Which relatives are considered first degree relatives?

A

Father, mother, siblings and children

33
Q

Which relatives are considered second degree relatives?

A

Aunts, uncles and grandparents

34
Q

Which relatives are third degree relatives?

A

First cousins

35
Q

Which modes of inheritance are possible in multi-system disorders?

A

All modes are possible:

  • Chromosomal: numerical or structural
  • Single gene disorders: autosomal dominant, autosomal recessive and X linked
  • Multifactorial: polygenic and environmental (e.g. haemachromatosis and diabetes)
36
Q

Why can gene mutations result in multi-system disease?

A
  • Several genes with diverse functions are involved
  • Single gene widely expressed in different tissues
  • Single gene tissue-specific expression but tissue integral part of many different systems
37
Q

What are the common problems in multi-system disease?

A
  • Variable expression within as well as between families
  • Present to a large variety of different specialists
  • Family history often missed
38
Q

What is the mode of inheritance and prevalence of NF1?

A

Autosomal dominant

1/2500-3500

39
Q

What are the diagnostic criteria for NF1 (need 2 for diagnosis)?

A
  • Cafe au lait spots: 6 or more
  • Neurofibromas: 2 or more
  • Axillary freckling
  • Lisch nodules (specks in iris)
  • Optic glioma
  • Thinning of long bone cortex
  • FH
40
Q

Name the further features of NF1?

A
  • Macrocephaly
  • Short stature
  • Dysmorphic Noonan look
  • Learning difficulties
  • Epilepsy
  • Scoliosis
  • Pseudoarthrosis of the tibia
  • Raised BP (due to renal a. stenosis or phaechromocytoma)
  • Neoplasia: CNS (optic gliomas) or endocrine
41
Q

Which features of NF1 are checked during the annual review?

A
  • BP
  • Spine for scoliosis
  • Tibia for unusual angulation
  • Visual acuity and visual fields
  • Educational assessment
  • Ask patient to report any unusual symptoms
42
Q

Which gene is involved in NF1?

A

17q - tumour suppressor gene

Mutations are different in different families and 50% are due to new mutations (usually paternal in origin)

43
Q

What are the main features of NF2?

A
  • Acoustic neuromas (usually bilateral)
  • CNS and spinal tumours
  • A few CAL spots
  • Gene is on chromosome 22
44
Q

What is the incidence of tuberous sclerosis (TS)?

A

1 in 7000 newborns

45
Q

What is the classic triad of tuberous sclerosis?

A

Epilepsy, learning difficulty and skin lesions

46
Q

What is the mode of inheritance of TS?

A

Autosomal dominant

47
Q

What are the genetics of TS?

A
  • Variable expression
  • Almost full penetrance if fully investigated
  • 2 genes on different chromosomes cause identical phenotypes (TSC1 and 2)
48
Q

What are the clinical features of TS?

A
  • Variable expression (asymptomatic to severe handicap)
  • Learning difficulty in 40%: autistic features common
  • Seizures in 65%: infantile spasms and myoclonic seizures
  • Skin lesions: angiofibromas and subungual fibromas etc.
  • Kidney: cysts and angiomyolipomata
  • Phakomas in eye
  • Rhabdomyomas in heart
49
Q

How would you investigate TS?

A
  • Exam: skin signs, Woods lamp, nails and retinal exam.
  • Cranial MRI
  • Renal USS
  • ECHO
50
Q

What is the mode of inheritance of myotonic dystrophy and what is the genetic cause?

A
  • Autosomal dominant

- CTG repeat: exhibits anticipation with increasing severity in each generation

51
Q

What are the clinical features of myotonic dystrophy?

A
  • Bilateral late-onset cataract
  • Muscle weakness, stiffness and myotonia
  • Low motivation, bowel problems and diabetes
  • Heart block
52
Q

What are the potential consequences of myotonic dystrophy?

A
  • Death post anaesthetic is possible if not monitored

- Congenital: death/severe muscle disorder and learning difficulty

53
Q

What are the possible mechanisms of adult onset genetic disease?

A
  • Single gene
  • Chromosomal
  • Mitochondrial
  • Multifactorial
54
Q

What are the clinical features of Amyotrophic lateral sclerosis?

A
  • Progressive muscle weakness, wasting and increased reflexes
  • Limb and bulbar muscles involved
  • Pure motor signs (with fasciculations)
  • Cognition spared
  • Death due to resp. failure
55
Q

Which forms of the superoxide dismutase are found in humans?

A
  • SOD1: located in the cytoplasm
  • SOD2: located in the mitochondria
  • SOD3: extracellular
56
Q

What is the benefit of superoxide dismutase?

A
  • Protects cells from free radical damage

- Also protects cells from DNA damage, lipid peroxidation, ionising radiation damage and protein denaturation

57
Q

What is the penetrance of ALS?

A

Incomplete - no certainty even with mutation analysis

58
Q

What are the genetic features of Huntington’s Disease?

A
  • Autosomal dominant
  • Adult Onset
  • Mutation: CAG expansion`
59
Q

What are the clinical features of Huntington’s disease?

A
  • Chorea
  • Athetosis
  • Myoclonus
  • Rigidity
  • Cognitive changes: poor planning/memory and subcortical dementia
  • Personality change: irritable, apathetic, loss of empathy, disinhibition and self centred
  • Psychiatric: depression, paranoia and psychosis
60
Q

What is the penetrance of Huntington’s ?

A

Fully penetrant

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