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GLA Y3S1 > Genetics > Flashcards

Genetics Flashcards

1
Q

What is the usual distribution pattern of an autosomal dominant condition

A
  • one copy is enough to cause the disease
  • is often present in every generation and shows a vertical pattern
  • you can check there is male to male transmission as this rules out the possibility of it being x-linked
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2
Q

example of autosomal dominant inheritance

A

achondraplaisa
- inherited breast or colon cancer
- APKD
- NF1
- HD

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3
Q

variable expressivity and complete and incomplete penetrance in autosomal dominant conditions

A

variable expressivity = effects people to different extents even with the same genotype

complete penetrance = they always get the disorder if they have the faulty gene

incomplete penetrance = sometimes dont get the disorder despite having the faulty gene

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4
Q

gonadal mosaicism

A

gonads can often carry more than one copy of the mutated gene on sperm/eggs

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5
Q

Autosomal recessive

A

requires two faulty copies of the gene to cause disease, if one copy the individual becomes a carrier

  • often shows a horizontal pattern -a prime examples of this is sickle cell disease
  • both males and females effected
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6
Q

examples of AR conditions

A
  • cystic fibrosis
  • PKU
  • spinal muscular atrophy
  • congenital adrenal hyperplasia but NOT HYPO
  • Wilsons disease
  • tay-sacks disease
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7
Q

X-linked recessive inheritance

A

effects boys more than girls as they can compensate with their other x-chromosome

  • knights move pattern NO MALE TO MALE
  • occasional manifesting female carriers due to skewed x-inactivation
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8
Q

compound heterozygosity

A

the presence of two different mutated alleles at a particular gene locus

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9
Q

example of x-linked recessive

A

duchess muscular dystrophy

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10
Q

expected proportions of offspring of a female heterozygote for an x-linked recessive condition

A

50% of sons effected
50% daughters are carriers

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11
Q

expected proportions of offspring of a male heterozygote for an x-linked recessive condition

A

none of his sons effected as boys get their X chromosome from their mother but all his daughters are carriers

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12
Q

X-linked dominant inheritance

A

vitamin D resistant rickets
looks like AD but no male to male transmission

other examples:
- incontinentia rickets
- rett syndrome

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13
Q

genetic anticipation

A
  • increasing severity and earlier age on onset in successive generations

in:
- HD
- Fragile x syndrome
- myotonic dystrophy

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14
Q

mitochondrial inheritance

A
  • smaller genome
  • circular
  • 37 genes with no introns

inherited inly from the mother but can be to variable extents
syndromes often affect muscle, brain and eyes

LEIGHS DISEASE

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15
Q

how do you detect point mutations

A

DNA sequencing
- Sanger sequencing which analyses one gene at a time
- Next generation sequencing which can do all or many genes at once

Allele-specific (ARMS) PCR
- special PCR that analyses only specific known point mutations

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16
Q

how do you test for the detection of sub-microscopic duplications and deletions

A

MLPA = PCR method which targets a small group of specific known positions - chromosomal loci where there might be a deletion

Chromosomal microarray (CMA) = this is genome wide.

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17
Q

How do you rapidly detect aneuploidies

A

this is searching for an abnormal number of chromosomes that is not a multiple of 23 such as trisomy 18

done by quantitative fluorescent PCR (QF-PCR)

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18
Q

old chromosome-based analysis methods

A

karyotyping which uses a microscope at 4 million base pairs

FISH uses a specific DNA probe that binds to one specific location on a chromosome, so you need to know what location you want to look at

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19
Q

whole chromosome analysis

A

Karyotyping
QF-PCR

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20
Q

Sub-microscopic deletions and duplications

A

FISH
MLPA - if you know the position
Chromosomal micro-array if you dont

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21
Q

point mutations

A

DNA sequencing or ARMS

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22
Q

NGS method

A

illumina method
- hundreds of millions of DNA fragments sequenced at once
- on a “flow cell”

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23
Q

huntingtons disease

A

onset between 30 and 50

progressive chorea, dementia and psychiatric symptoms

AD with genetic anticipation

caused by a CAG repeat unit within the coding sequence which encodes a polyglutamine tract and this expansion causes insoluble protein aggregates and neurotoxicity

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24
Q

myotonic dystrophy

A

AD also with genetic anticipation

  • progressive muscle weakness in early adulthood
  • can also result in myotonia and cataracts

unstable mutation of a CTG repeat
- abnormal DMPK mRNA which has an indirect toxic effect upon splicing of other genes e.g. the chloride ion channel CLCN1 gene which causes myotonia

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25
Q

cystic fibrosis

A

AR

Recurrent lung infections
exocrine pancreatic insufficiency

screening in newborns by immunoreactive trypsin IRT) level

This can be confirmed by DNA testing for CF mutations and/or sweat testing for increased chloride conc

CFTR mutations which result in defective chloride ion channels and therefore an increased thickness of secretions

most common is F508del

26
Q

NF1 common presentations

A

cafe au lait macules and neurofibromas, short stature and macrocephaly

learning difficulty in 30%

Lisch nodules (2 or more) that can be seen on a slit-lamp

27
Q

what is the pathology of duchess muscular dystrophy

A

creatine kinase leaks out of damaged muscle fibres into serum (into blood)

boys with DMD will have massively increased levels of creatine kinase in serum from birth before any symptoms become noticeable

28
Q

Duchene muscular dystrophy vs Becker muscular dystrophy

A

DMD:
- onset at roughly 3
- wheelchair by 12

BMD:
- onset at roughly 11
- Wheelchair much later or not at all

29
Q

Fragile X syndrome

A

X-linked recessive most common cause of inherited learning disability

30
Q

what is a full mutation in fragile x syndrome

A

> 200

31
Q

Edwards syndrome

A
  • trisomy 18
  • small chin
  • clenched hands with overlapping fingers
  • malformations of heart, kidney and other organs
32
Q

patau syndrome

A
  • trisomy 13
  • congee heart disease is usual
  • many die within a month
  • cleft lip & palate
    micropthalmia
    abnormal ears
    clenched fists
33
Q

what is the role of tumour suppressor genes

A

inhibit progression through the cell cycle
some promote apoptosis
some act as DNA repair genes

34
Q

porto-oncogenes role

A

normally stimulate the cell cycle, these when effected by a gain of function mutation can lead to tumour formation

35
Q

what happens when a mutation occurs in the tumour suppressor genes

A

these mutations result in a loss of function and usually requires loss of a normal allele (gene copy) (REFER TO TWO HIT THEORY)

36
Q

what are DNA repair genes

A

these are a sub-type of TSG which act to minimise genetic alterations
important in breast/ovarian and colorectal hereditary cancer predisposition syndromes

37
Q

what is the cause of most inherited cancer predispositions

A

due to the inheritance of an altered TSG which then involves the subsequent activation of the wild-type (normal) allele, THIS IS THE TWO HIT HYPOTHESIS

38
Q

If a patient has breast and ovarian cancer history what is the likely mutation

A

BRCA1

39
Q

If there is male breast cancer present in the family what is the likely mutation

A

BRCA2

40
Q

If you have a BRCA1 mutation what is the likelihood of developing breast cancer by the age of 70

A

50-80% this is an example of incomplete penetrance

and 20-50% for ovarian cancer

41
Q

If you have a BRCA2 mutation what is the likelihood of developing breast cancer by the age of 70

A

50-80% breast cancer
10-20% ovarian
5-6% breast cancer in men

42
Q

preventative measures for breast cancer

A

examinations
screening such as mammography or MRI

if you have BRCA1 OR BRCA2 mutations then you may be offered
- prophylactic bilateral mastectomies
- prophylactic oophorectomies (removal of the ovaries)

43
Q

treatment for ovarian cancer

A

PARP

44
Q

common colon cancer mutation

A

hereditary non-polyposis colon cancer also known as Lynch syndrome

Some FAP = familial adenomatous polyposis

45
Q

hereditary non-polyposis colon cancer also known as Lynch syndrome

A
  • usually only a few polyps, has to be less than 10, in the ovary stomach or uterus

this is due to inheritance mutation in MMR system genes

46
Q

what genes cause HNPCC

A

MLH1
MSH2
MSH6
PMS2

47
Q

FAP

A

congenital hypertrophy of the retinal pigment epithelium

from APC gene on chromosome 5
patients get annual bowl screening from age 11

48
Q

MYH/MUTYH polyposis

A

AR
2 yearly colonoscopy
like a mild form of FAP

49
Q

Li Fraumeni syndrome

A

rare AD cancer predisposition syndrome
- great cancer
- brain tumours
- sarcoma
- leukaemia
- adrenocortical carcinoma

mutations in TP53 gene

50
Q

what would you want to know from a patients clinical history

A

what were the age of onset of symptoms and how is the progression

51
Q

what would you want to know from a patients family history

A

consanguinity ? miscarriages? still births?

52
Q

what would you want to note from a patients examination

A
  • any dysmorphic features
  • normal growth (height, occipital-frontal circumference - OFC)
53
Q

examples of dysmorphic features

A

smooth philtrum
correct number of fingers and toes
are they joined (syndactyly)
polydactyly (too many?

eyes:
slant of palpebral fissures
spacing

ears:
- size, shape, position (are they low set)
- rotated anteriorly or posteriorly

hands
- palmar creases

54
Q

Rubinstein Taybi syndrome

A

down slanting palpebral fissures
microcephaly
broad thumbs and big toes
intellectual disability

55
Q

What are some new/future developments for treatment and testing in genetics

A

more use of non-invasive and prenatal diagnosis NIPD (on maternal plasma and free fetal DNA)
this could aid with
- testing for metal sex determination for X linked conditions as you would test for Y chromosome DNA
- for paternal mutations could search for FGFR3
Can also test for anaeploidy which can be confirmed by CVS or amnio

Increase use of next gen sequencing of gene panels which tests whole exomes and while genomes

more gene therapy

more precision medicine

56
Q

what is precision medicine

A

this would be the selection of medication after analysing DNA to increase the efficacy and reduce the side effects

examples of this include treatment for CF

if you undergo gene testing for the G551D mutation which blocks the opening of the CFTR chloride ion channel the ivacaftor (kalydeco) can reopen the channel so this would be prescribed and you would know it would work

57
Q

use of precision medicine in cancer

A

the use of one or more clinical biomarkers to identify therapies more suited for specific patients such as in NSCLC (the presence of particular EGFR gene mutations indicate that tumour may respond to tyrosine kinase inhibitors

58
Q

what are the current gene therapy strategies

A

treating the gene or its expression (transcription, splicing and translation
OR
replacing the gene

59
Q

what are some future therapies for DMD

A

the use of a drug to permit read-through of premature stop codons such as Ataluren (this is a small molecule that may cause read through of premature stop codons in 10-15% of cases of DMD allowing the ribosome to finish synthesising the protein (dystrophin)) or PTC124

60
Q

genetic heterogeneity

A

one disorder having several genetic causes

61
Q

Pleiotropy

A

one gene causes more than one condition or train such as RET gene causes MEN2 (AD) and also Hirschprungs Disease (AR)

GLA Y3S1 (13 decks)

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