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4TH YEAR - CSIM2 > Genetics > Flashcards

Genetics Flashcards

1
Q

What is a polymorphism?

A

The occurrence of two or more genetically determined phenotypes in a certain population

NB - this is benign, in contrast to a mutation

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2
Q

What is a variant of unknown significance?

A

When the lab cannot determine whether a gene change is deleterious (harmful) or a benign polymorphism

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3
Q

What is a predictive test?

A

A test done in a newborn to detect genetic characteristics that have been proven to exist in the parent, but have not yet altered the child phenotypically

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4
Q

What is cytogenetics?

A

The field of looking at ones chromosomes using:

  • Karyotype
  • FISH
  • array cGH
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5
Q

What is sequencing?

A

Molecular testing to look at anything from a single gene base to a whole exam

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6
Q

Describe autosomal dominant inheritance

A

If one parent is affected, there is a 50% chance that the child will be

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7
Q

Describe autosomal recessive inheritance

A

If one parent is affected, there is a 25% chance that the child will be

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8
Q

Describe mitochondrial inheritance

A

The trait can only be inherited from the mother, as it lies in the mitochondria

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9
Q

What is penetrance?

A

The proportion of individuals with a genetic mutation that manifest the disease

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10
Q

What is genetic counselling?

A

The process by which patients or relatives at risk of a genetic disorder are advised of the consequences of the disorder, the probability of transmitting it and ways in which it can be prevented

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11
Q

How are the following genetic conditions diagnosed:

a) NF1
b) Marfans
c) early onset epilepsy

A

a) clinical
b) specific gene test
c) gene panel as there is no specific causative gene

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12
Q

What is a triple repeat disorder? Give an example?

A

Dominant mutation caused by an increased number of copies of a tandemly repeated trinucleotide

eg. Huntingtons - increased CAG repeat over 40 repeats

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13
Q

What is anticipation?

Give 2 conditions which show this pattern

A

When a genetic condition becomes more severe in successive generations

Huntingtons, myotonic dystrophy

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14
Q

What is age related penetrance?

Give 3 conditions which show this pattern

A

When the frequency of disease changes at different ages

Huntingtons, myotonic dystrophy, fragile X

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15
Q

What is genetic heterogeneity?

Give a condition which shows this pattern

A

When a clinical phenotype can be caused by mutations in any one of a number of different genes

Long QT syndrome

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16
Q

What is the genetics of Marfans syndrome?

A

FBN1 mutation leading to skeletal, ocular, cardiac complications

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17
Q

What is variable expression?

Give a condition which shows this pattern

A

When the phenotype differs amongst individuals carrying the same genotype

Marfans

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18
Q

What is the genetics and features of NF1?

A

Mutation in NF1 gene, causing cafe au last spots, hearing difficulties and bone deformities.

Shows 100% penetrance and variable expression

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19
Q

What is the genetics and features of tuberous sclerosis?

A

Mutation in TSC1/2 genes, causing skin changes, renal lesions, cerebral lesions and seizures

Shows 100% penetrance and variable expression

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20
Q

How is the ApoE allele involved in alzhemiers?

A

Different forms of the allele can affect risk of disease.
E2 - protective
E3 - normal
E4 - risk allele

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21
Q

What syndrome causes isolated cleft lip and palate?

A

Van de Woude syndrome

autosomal dominent, variable expression

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22
Q

What syndrome causes cleft lip, cardiac problems and polydactyly?

A

Patau’s syndrome

trisomy 13, usually incompatible with life

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23
Q

What syndrome will a de novo mutation in CHD7 cause?

A 
CHARGE syndrome
Coloboma (hole in eye)
Heart defects
Atresia of nasal passage
Retardation of growth
Genital and urinary tract abnormalities
Ear abnormalities/hearing loss
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24
Q

Describe the features of fetal valproate syndrome

NB - specify what facial features

A

Cardiac defects, cleft lip, genitourinary abnormalities, developmental problems

Face - tall forehead, medial eyebrow deficiency, flat nasal bridge, shallow flirt, long upper lip

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25
Q

Give 5 examples of teratogens

A 
Infection (CMV/rubella)
Tobacco
Thalidomide
Radiation
Alcohol
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26
Q

What is aneuploidy?

A

An abnormal number of chromosomes (i.e.. not 46)

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27
Q

Give an example of a trisomy

A

Downs syndrome (21)
Pataus (13)
Edwards (18)

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28
Q

Give an example of a monosomy

A

THERE IS ONLY ONE VIABLE MONOSOMY - 45X (Turners Syndrome)

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29
Q

What is a balanced structural chromosomal abnormality?

A 
When breakage of chromosome segments results in no loss or gain of genetic material
3 Types:
Reciprocal translocation
Inversion
Insertion

These can usually be seen on a karyotype

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30
Q

What is reciprocal translocation?

A

A balanced chromosomal abnormality involving exchange of genetic material from two non homologous chromosomes

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31
Q

What is inversion?

A

A balanced chromosomal abnormality when a segment is reversed end to end within the chromosome

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32
Q

What is insertion?

A

A balanced chromosomal abnormality in which a portion of one chromosome is deleted from its normal place and inserted into another chromosome

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33
Q

How can a balanced chromosomal abnormality be detected?

A

Look at karyotype

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34
Q

What is an unbalanced structural chromosomal abnormality?

A

When breakage of chromosomal segments results in addition or subtraction of genetic material
2 types:
Deletion (eg. Di George Syndrome)
Duplication (extra genetic material)

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35
Q

How can an unbalanced structural chromosomal abnormality be detected?

A

Look at FISH or arrayCGH

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36
Q

What is Robertsonian Translocation?

A

Breakage of two acrocentric chromosomes (ie. one long arm one short arm)

Translocation then leads to one long large chromosome with most of the genetic material, and one small one which is usually lost within a few cell divisions.

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37
Q

Which chromosomes can undergo robertsonian translocation?

A

13, 14, 15, 21, 22

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38
Q

How does microarray work?

A

DNA based technique that examines the whole genome for gains/losses of genetic material by looking at changes in the COPY NUMBER VARIANTS (repeats)

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39
Q

How does FISH work?

A

Segments of DNA are labelled with fluorescent dye ‘probes’ which bind to complimentary parts of the chromosome

40
Q

What is FISH useful for?

A
  • Detection of chromosome rearrangements that are too small for karyotyping
  • This includes small deletions, inversions and translocations
41
Q

What is karyotyping?

A

Staining of condensed chromosomes to produce a visible sample of cells in metaphase

42
Q

What is clinical exome sequencing?

A

Mass sequence of the whole exome to detect single nucleotide variants.

This may involve looking at the parent genotypes swell to see if variants are significant

43
Q

What is clinical exome sequencing for?

A

Detection of variants, single nucleotide changes, inorganic mutations, as well as larger deletions/gains

44
Q

What is the most common autosomal recessive disorder?

45
Q

If you are a carrier of a disease, what are the options if you are trying for a baby?

A
  • Take your chances
  • Adoption
  • Pre-implantation genetic testing
  • Free cell foetal DNA
  • Chorionic villi sampling
  • Post natal heel prick/cord blood
46
Q

If a female is a carrier of an X-linked recessive condition, what are the outcomes for her offspring?

A
  • Female carrier
  • Affected male
  • Unaffected male
  • Unaffected female
47
Q

If a male is affected by an X-linked recessive condition, what are the outcomes for his offspring

A
  • Female carrier
  • Unaffected male

ie. you dont get male-male transmission

48
Q

Give 2 examples of X-linked inheritance

A

Haemophilia

Fabry Disease

49
Q

What is X inactivation?

aka Lyonisation

A

At the time of implantation one of the female X chromosomes gets inactivated, as it is a duplicate of the genetic material.

On the inactive chromosome, it is silenced by XIST.

On the active chromosome, XIST is methylated so that it is non-functioning, meaning that the X chromosome remains on.

50
Q

What is XIST?

A

A region on an X chromosome that if active, silences the rest of the X chromosome (except PAR1/2)

51
Q

What is PAR1/2?

A

These are pseudoautosomal regions, which are homologous sequences of nucleotides, containing genes that are inherited like autosomal genes.

52
Q

What is skewed X inactivation?

aka Mosaicism

A

When the inactivation of one X chromosome is favoured over the other.

53
Q

What does strong skewing in females suggest?

A

It suggests they are carriers of an x-linked condition.

54
Q

What are some X-linked conditions that show very little mosaicism? ie. disease only really affects males

A

Hunter syndrome
Lesch-nyhan syndrome
G6PD deficiency

55
Q

What are some X-linked conditions that cause a mutation so severe that it usually affects females, and is usually lethal in males?

A

Rett Syndrome

Incontinentia pigmenti

56
Q

What are the symptoms of muscular dystrophy?

A

Muscle weakness, exhaustion

57
Q

What investigations can be done into someone with suspected muscular dystrophy, and what does it show?

A

Muscle biopsy shows degeneration, fibrosis and scarring.
Immunostaining shows absent sub-sarcolemmal dystrophin.

Micro assay shows intragenic mutation

58
Q

What do you call the form of muscular dystrophy that you get from skewed x-inactivation? ie. a milder form

59
Q

What is the difference in the genetics between DMD and BMD?

A

DMD - mutation causes a frameshift that leads an abnormal stop codon and formation of a truncated non-functioning dystrophin molecule.

BMD - mutation causes a frameshift which preserves the reading frame (eg. deletion of 6 base pairs) but results in a shorter molecule, but with some preserved function.

60
Q

How can X-linked disorders be treated?

A

Enzyme replacement

Exon skipping - alter frameshift

61
Q

What is genomic imprinting?

A

An epigenetic phenomenon that causes genes to be expressed in a PARENT OF ORIGIN SPECIFIC MANNER, due to methylation.

ie. certain genes will always be methylated/demethylated depending on which parent you get them from

This only occurs in a small proportion of genes, most cells have expression from both alleles

62
Q

Describe the imprinting behind SDHD

A

If you inherit an SDHD mutation from your father it will be demethylated, and you will therefore develop paragangliomatosis

If you inherit an SDHD mutation from you mother, it will be methylated, and therefore silenced, and you will be a carrier

63
Q

Describe the imprinting behind Prader Willi/Angelman syndrome

A

Angelmann - deletion of part of chromosome 15q13 in the mum means that the dads copy, which is usually silenced, has to be expressed.

Prader Willi - deletion of part of chromosome 15q13 in the dad means that the mums copy, which is usually silenced, has to be expressed.

Willi - problem with the dad

This is an example of uniparental disomy

64
Q

What are the symptoms of Prader Willi?

A

Obesity, intellectual impairment, T2DM, weak muscles, poor feeding initially

65
Q

What are the symptoms of Angelman syndrome?

A

Small head, happy nature, intellectual impairment, seizures, fascination with water

66
Q

What is the founder effect?

A

Over-representation of a gene defect in a small community

67
Q

What is karyotyping good for?

A
  • Chromosomes looked at down a light microscope

- Used for prenatal screening and looking ofr aneuplodies

68
Q

What genetic technique would you use to look at Angelman/Prader Willi?

69
Q

What is MLPA?

A

Amplication of DNA using specific probes, using PCR

This allows you to look for SNPs mutations, duplications, analysis of DNA methylation etc

70
Q

When is MLPA often used?

A

Prenatal diagnosis

71
Q

What is the genetic mutation in Marfans

A

Mutation in FBN1 gene on chromosome 15q

72
Q

Describe the features in someone with Marfans

A

Tall and slim with long limbs and fingers (arachnodactyly)

73
Q

What are the complications in Marfans:

a) cardiac
b) ocular
c) lungs

A

a) Dilation of the aortic root
Ascending aortic aneurysm
Aortic dissection

b) Lens dislocation
c) Spontaneous pneumothorax

74
Q

What is the genetic mutation in achondroplasia?

A

FGFR3 mutation

Although often it is sporadic!! (80%)

75
Q

Describe the phenotype of a patient with achondroplasia

A

Short hands, square hands, frontal bossing, short stature ‘dwarfism’

76
Q

What causes trisomy?

A
  1. Non-disconjunction at meiosis I or II - you will end up with a gamete that has 2 chromosomes instead of 1
  2. Robertsonian translocation
77
Q

Describe some of the characteristics of someone with Downs Syndrome

A 
Generalised hypotonia
Prominent epicanthic folds
Protruding tongue
Short broad hands with palmar crease
Intellectual impairment
78
Q

What is the genotype of someone with Klinefelters syndrome?

79
Q

Describe the phenotype of Klinefelters syndrome

A 
Tall male
Feminine body shape
Libido loss
Gynaecomastia
Infertility

Usually this doesn’t present until puberty

80
Q

What is the genotype of someone with Turners syndrome

81
Q

What are the complications of Turners?

A

Congenital heart disease

Structural renal abnormalities

82
Q

In what condition would you find streak ovaries?

A

Turners Syndrome - causes primary amennorhoea and infertility

ALWAYS HAVE OVARIAN AGENESIS

83
Q

What is uniparental disomy?

A

When you inherit both homologs of a chromosome pair from 1 parent (instead of one from each)

84
Q

Which teratogens cause embryo malformation?

A

Alcohol
Warfarin
Rubella, VZV, zika, toxoplasmosis

85
Q

Which teratogens cause neural tube defects?

A

Methotrexate (interferes with folate)
Sodium valproate
Phenytoin
Carbamazepine

86
Q

What is freidreichs ataxia?

A

Autosomal recessive disease causing progressive damage to the nervous system

87
Q

What is neuroferritinopathy?

A

Dominant mutation of ferritin, causing chorea dystonia, parkinsonism

88
Q

What is the role of copper?

A

Enzyme cofactor

89
Q

What are the symptoms of copper deficiency?

A

Fatigue, normocytic anaemia, peripheral neuropathy, EPS

90
Q

What are the symptoms of copper overload?

A

ACUTE: GI spasm, kidneys, haematemesis, rhabdomyolysis
CHRONIC: Cirrhosis, diabetes, renal, neuropsychiatric

91
Q

What is Wilsons disease?

A

Recessive mutation causing ATPgammaB deficiency and copper retention

92
Q

What tests are used to diagnose Wilsons disease?

A
  • Low caeruloplasmin
  • High urine copper
  • MRI - ‘panda face; copper deposits
93
Q

What are the features of Wilsons disease?

A

Kayser-fleischer rings in the eyes, cirrhosis, cardiomyopathy, anxiety

94
Q

How is Wilsons disease treated?

A
  • BAL
  • Penicillamine
  • Zinc
95
Q

What is Menkes disease? Describe the pathophysiology

A

X linked recessive mutation in the copper transport gene (ATP7A) which makes a protein that regulates absorption. Less copper is released from enterocytes to the blood, causing deficiency.

96
Q

What are the features of Menkes disease?

A

Developmental delay, seizures, hair/skin/nail defects

97
Q

How is Menkes treated?

A

Give CU histidinate

4TH YEAR - CSIM2 (20 decks)

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