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3rd year > Genetics > Flashcards

Genetics Flashcards

1
Q

How do disease-associated mutations alter protein function?

A

Can cause it to be non-functional.

Or reduce its function.

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2
Q

What percentage of breast and ovarian cancer is hereditary?

A

10%

15% for breast family clusters.

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3
Q

What percentage of colorectal cancer is hereditary?

A

10-30%

Lynch syndrome.

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4
Q

What are Germline mutations?

A

Mutation in egg or sperm which then affects all cells in the offspring.
Cause cancer family syndromes.

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5
Q

What are somatic mutations?

A

Occur in nongermline

Nonheritable

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6
Q

If there is a problem with oncogenes what happens?

A

Accelerated cell division - 1 mutation is sufficient role in cancer development.

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7
Q

Tumour suppressor gene problems what happens?

A 
1st mutation (susceptible carrier) 
2nd mutation (leads to cancer)
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8
Q

What is the main mechanism for familial cancer?

A

Faulty DNA mismatch repair.

Base pair mismatch and then mutation introduced by unrepaired DNA.

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9
Q

What happens in Lynch syndrome?

A

Mutation is mismatch repair genes.

Excess of colorectal, endometrial, urinary, ovarian and gastric cancers.

Adenoma - carcinoma sequence for polyp formation.

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10
Q

Diagnosis age and site in HNPCC?

A

Early but variable age at CRC diagnosis ( about 45).

Tumour site in proximal colon predominates.

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11
Q

What can be used as a preventative treatment for Lynch?

A

Prophylactic Aspirin - for gene carriers.

don’t know dosage

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12
Q

BRCA 1 is associated with what cancers?

A

Breast (60-80%)
Second primary breast (40-60%)
Ovarian (20%-50%)

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13
Q

What is BRCA2 associated with?

A

Increased risk of Prostate and Breast in men.

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14
Q

When is hereditary cancer syndrome suspected?

A

Cancer in 2 or more close relatives.
Early age at onset.
Multiple primary tumours.
Characteristic pattern of tumours. (breast and ovary)
Autosomal dominant transmission evidence.

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15
Q

Cancer family history - what is key?

A

Accurate risk assessment.
Effective genetic counselling.
Appropriate medical follow up.

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16
Q

What is the process for cancer genetics?

A

Obtain detailed family history.
Confirm diagnoses of cancer.
Risk estimation.
Counselling.

17
Q

Breast cancer surveillance options?

A

Breast awareness.
Early clinical surveillance 5yr Annual or clinical brest exams.
Mammography.
MRI screening those at highest risk.

18
Q

What does a prophylactic mastectomy do?

A

Removes most of breast tissue.
Significantly reduces breast cancer risk in women with fam history.
BRCA1 mutation-positive women breast cancer incidence reduced to 5%.

19
Q

What does a prophylactic oophorectomy do?

A

Eliminates risk of primary ovarain cancer; however, peritoneal carcinomatosis may still occur.
Induces surgical menopause but HRT till 50 does not change BRCA risk.
Risk of subsequent BRCA halved in mutatrion-positive women.

20
Q

What are the benefits of genetic testing?

A

Identifies highest risk.
Non-carriers identified.
Allows early detection.
May relieve anxiety.

21
Q

What are the risks and limitations to genetic testing?

A

Does not detect all mutations.
Continued risk of sporadic cancer.
Efficacy of interventions variable.
May result in psychosocial or economic harm.

22
Q

What are the modes of inheritance in multi-system disorders?

A

Chromosomal - numerical e.g. trisomy 21. Structural.
Single gene disorders - Autosomal dominant e.g. TS, NF1
Autosomal recessive e.g. CF
X-linked e.g. Duchenne muscular dystrophy.
Multifactorial - polygenic, environment.

23
Q

Why are multi-systems involved in these mutations?

A

Several genes with diverse functions are involved (chromosomal).

Single gene widely expressed in different tissues.

Single gene tissue-specific expression but tissue integral part of many different systems.

24
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 easily missed.

25
Q

What is Neurofibromatosis Type 1 (NF1)?

A

Autosomal dominant

Prevalence 1/2500-3500

26
Q

What are the NF1 signs and symptoms?

A 
Need 2+ for diagnosis:
Cafe au lait spots - 6 or more.
Neurofibromas - 2 or more.
Axillary freckling
Lisch nodules 
Optic glioma 
Thinning of long bone cortex 
Fam History
Short stature 
Macrocephaly
Learning difficulties 
Epilepsy 
Scoliosis
Raised BP
Neoplasia (CNS)
27
Q

Diagnosis and Management of NF1

A

Clinical diagnosis using diagnostic criteria.
Management:
Annual review of affected individuals and at risk children until diagnosis can be excluded.
- BP
- spine for scoliosis
- tibia for unusual angulation
- Visual acuity and visual fields
- educational assessment
- ask patient to report any unusual symptoms

28
Q

Genetics of NF1

A

Autosomal dominant
Variable expression (inter/intra)
Gene identified - 17q - tumour supressor gene.
Mutations different in different families.
50% due to new mutations.

29
Q

What are the main features of NF2?

A 
Acoustic neuromas 
Usually bilateral 
CNS and spinal tumours 
Few cal spots
On chromosome 22
30
Q

What is Tuberous Sclerosis?

A

Incidence 1 in 7000 newborns
Classic triad: Epilepsy, Learning difficulties, Skin lesions.
Autosomal dominant
Hamartomas in different organs.

31
Q

What are the genetics behind TS?

A

Autosomal dominant
Variable expression
Almost full penetrance
2 genes on different chromosomes both cause TS with identical phenotypes. (TSC1/2)

32
Q

What are the clinical features of TS?

A 
Multi-system (lung,skin,heart,brain,kidney,other)
Variable expression 
Learning difficulty 40%
Seizures 65% 
Skin lesions (depigmented macules)
Kidney (cysts)
Phakomas in eye 
Rhabdomyomas in heart.
33
Q

Screening of at-risk relatives?

A

Siblings and parents may be mildly affected.
Surveillance and genetic counselling.
Clinical exam.
Cranial MR scan, renal US, Echocardiogram.

34
Q

What is myotonic dystrophy?

Signs and symptoms?

A 
Autosomal dominant
CTG repeat.
Bilateral late-onset cataract.
Muscle weakness, stiffness, myotonia. 
Low motivation, bowel problems, diabetes mellitus.
Heart block
Death post-anaesthetic risk.
35
Q

What are the mechanisms of adult onset genetic disease?

A

Single gene
Chromosomal
Mitochondrial
Multifactorial (genes and environment)

36
Q

What makes a disease a shared genetic heritage?

A

Genetic disease affects families, not individuals.

Discovery of a genetic disorder implies a risk for relatives.

37
Q

What are possible advantages to predictive testing for Huntington’s disease?

A

Uncertainty of gene status removed.

3rd year (22 decks)

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