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MCD > Genetics > Flashcards

Genetics Flashcards

1
Q

What proportion of newborns do congenital defects affect

A

1 in 50

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2
Q

What are the 2 broad types of congenital defect

A

Single and multiple

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3
Q

What is malformation and give an example

A

Single congenital defect

Morphological defect of an organ due to abnormal development e.g. cleft lip, atrial septal defect

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4
Q

What is disruption and give an example

A

Single congenital defect

Morphological defect of an organ from intrinsic breakdown or interference with a normal process e.g. amniotic band

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5
Q

What is deformation and give an example

A

Single congenital defect

Abnormal form shape or position due to mechanical factors e.g. club foot

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6
Q

What is dysplasia and give an example

A

Single congenital defect

Abnormal organisation of cells into tissue and its morphologic results e.g. thanatophoric dysplasia

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7
Q

What is a sequence

A

Multiple congenital defects

Pattern of abnormalities derived form a single known or preserved prior anomaly e.g. Potters sequence

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8
Q

What is a syndrome

A

Multiple congenital defect

Multiple anomalies thought to be pathogenically related that is not a sequence e.g. Downs

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9
Q

What is an association

A

Multiple congenital defects

Non-random occurrence in 2 or more individuals of multiple abnormalities e.g. VATER association

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10
Q

Describe the packaging of DNA

A

DNA
Gene
Chromosome
Genome

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11
Q

What is the normal human karyotype

A

22 chromosomes and 1 sex chromosome (haploid) from 1 parents

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12
Q

What is nomenclature of chromosomes based on

A

bands
long arm= P
short arm = Q

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13
Q

What are the possible structural abnormalities of chromosomes

A 
duplication 
inversion 
deletion
ring - telomeres
translocation - Transfer of genetic material from one chromosome to another
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14
Q

Describe Robertsonian translocation

A

The short arms (q) are lost while the long arms are combined
These become fused and therefore do not separate during division
If there is a balance, it is unlikely that there will be an abnormal phenotype
If unbalanced, disruption of a gene may occur or a fusion product

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15
Q

Give the possible consequences of robertsonian translocation on reproduction with a normal cell

A

normal
monosomy (lethal)
trisomy

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16
Q

Which monosomy abnormality is not lethal

A

Turner’s

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17
Q

Define aneuploidy

A

Loss or gain of 1 or more chromosome

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18
Q

Describe the different types of numerical abnormalities in chromosome

A

monosomy - loss of 1 chromosome
disomy - normal
trisomy - gain of 1 chromosome
tetrasomy - gain of 2 chromosome

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19
Q

Give 3 examples of trisomy

A

Downs - 21
Edwards - 18
Patau - 13

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20
Q

What is the most common form of trisomy

A

Chromosome 16

Lethal and leads to miscarriage

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21
Q

Describe the features of trisomy 21

A 
hypotonia
lethargy
excess nuchal skin
Cranofacial features
Sandal gap
Single palmar crease
Septal and heart defects
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22
Q

What are the causes of trisomy 21

A

Non-disjunction in meiosis 1 where homologous chromosomes fail to separate
Translocation
Mosaicism

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23
Q

What is mosaicism caused by

A

mitotic non-disjunction

Children are less severely affected

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24
Q

Define dosage compensation

A

ensures equivalent gene expression in both sexes

Inactivation of an X chromosome in females (lyonisation)

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25
Q

What is Turner’s syndrome and its features

A

monosomy X
Loss of the X or Y in paternal meiosis
Webbed neck, low ears, normal intelligence

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26
Q

What is Klinefelter’s syndrome

A

47 XXY
X from either parent
Phenotypically male, learning disability, taller, learning disability, infertility

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27
Q

Identify the symbols used in pedigree charts for proposiatus, X-linked carrier, unspecified sex, abortion, unidentical twins and identical twins

A 
arrow = proposiatus (first)
solid with an outline = X-linked carrier
diamond = unspecified sex
little circle = abortion of still birth
diagonal lines = unidentical twins
diagonal twins + horizontal = identical twins
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28
Q

Describe the inheritance patterns for an autosomal dominant disease

A 
Only 1 copy is needed to be presented in the phenotype
At least one parent is affected
M or F
Vertical transmission
Age of onset decreases further down
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29
Q

Describe Huntington’s disease

A

Autosomal dominant disease
Motor, cognitive and psychiatric disfunction
Caused by CAG repeats
The greater the no. of CAG, the more severe

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30
Q

Describe the inheritance patterns for an autosomal recessive disease

A

Both alleles must abnormal to be presented in the phenotype
No affected parents
M or F
Usually very little family history

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31
Q

Describe cystic fibrosis

A

Autosomal recessive disease
Thick mucous produced in the lungs
breathing problems, infectious, blocks the pancreas
CTFR gene incorrectly folded

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32
Q

Describe the inheritance patterns for a X-linked recessive disease

A

No affected parents
Only M affected
Transmitted by F carriers

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33
Q

Describe haemophilia

A

X-linked recessive disease
Blood clotting disorder
Easy bruising and bleeding
Types A and B

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34
Q

Give an example of how the same gene can have different mutations

A

The CFTR gene mutating can cause cystic fibrosis or CAVD

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35
Q

Give an example of how mutations in different genes can cause the same disease

A

Mutations in genes A and B can both cause haemophilia

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36
Q

Give an example of how different genes and inheritance can cause the same disease

A

AD and AR will cause epidermis bullosa

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37
Q

Define Mendelian inheritance

A

Individuals inherit and transmit to their offspring one out of the 2 alleles present in homologous chromosomes

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38
Q

Define polymorphism

A

Mutation present in >1% of the population which may contribute to complex disease

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39
Q

What are the types of point mutation

A

missense (1 amino acid for another)

nonsense (stop codon for an AA)

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40
Q

Define incomplete inheritance

A

Symptoms are not always present in an individual with a disease-causing mutation

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41
Q

Define variable expressivity

A

Disease severity may vary between individuals with the same disease-causing mutation

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42
Q

Define phenocopy

A

Having the same disease but with a different underlying cause

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43
Q

Define epistasis

A

Interaction between disease gene mutations and other modifier genes which can affect genotype

44
Q

What are dominant conditions usually caused by and how may this be resolved

A

mutations that result in the presence of a toxic protein

Switch off the gene or neutralise the produced protein

45
Q

What are recessive conditions usually caused by and how may they be resolved

A

Mutations that lead to the absence of a functional protein

Restore tha activity of the missing protein

46
Q

What are co-dominat conditions usually caused by and how may they be resolved

A

Both the mutated and normal genes are apparent

Switch off the abnormal gene of neutralise the protein

47
Q

What is the epigenome

A

Transcriptome
Surrounds the genome
Non-mendelian inheritance

48
Q

What is imprinting

A

Involves DNA methylation. The genome carries an imprint of the parental origin.
75 genes are affected
The DNA sequence remains normal while function changes
Reflects that parental origin of chromosomes is important

49
Q

What is methylation

A

Methyl groups are attached to the 5 position of the pyrimidine ring cytosine on DNA
Decreases gene expression as it blocks transcription factors

50
Q

Describe Prader-Willis syndrome

A

Loss of function of the paternal chromosome

Critical region is deleted OR 2 maternal copies are inherited (uniparental isodomy)

51
Q

What are the symptoms of Prader-Willis syndrome

A 
Hyperphagia (overeating with loss of regulatory process)
Obesity
Mental retardation
Hypotonia (reduced muscle tension)
short
Infertile
52
Q

Describe Angelman syndrome

A

Loss of function of the maternal chromosome

Imprinting defects OR UB3A mutations

53
Q

How is Prader-Willis syndrome treated

A

Diet restriction
Exercise for muscle
Growth hormones
Hormone replacement

54
Q

What is the karyotype of the mitochondria

A

36 genes

2-10 copies are circular genomes

55
Q

Describe mitochondrial inheritance

A

Only inherited through females

The sperm lose their mitochondria as they meet the egg

56
Q

What is heteroplasmy

A

Mixture of mitochondria with some containing mutant DNA while others are maternal

57
Q

Give some examples of mitochondrial diseases

A 
MELAS
LHON
MERRF
DEAF
NARP
58
Q

Describe MELAS

A

Mitochondrial myopathy Encephalopathy Lactic Acidosis and Stroke
Progressive neurodegenerative disorder
The muscle and brain have lots of mitochondria so they are heavily affected

59
Q

What are the symptoms of MELAS

A

muscle weakness
episodic seizures
stroke-like episodes
vomiting

60
Q

Describe LHON

A

Leber’s hereditary Optic Neuropathy

More common in males

61
Q

What are the symptoms of LHON

A

Bilateral vision (loss of central vision)
Optic atrophy
Blindness

62
Q

What are the emerging therapies for LHON

A

3 parent babies

donor gives an empty egg cell

63
Q

What is the newborn screening programme in the UK

A

Physical exam
Hearing test
Blood spot (Guthric acid) - sickle cell, cystic fibrosis, PKU(9 in total)

64
Q

Describe PKU and its symptoms and treatment

A 
Phenylketonuria 
Deficiency of phenyladenine hydroxylase 
Severe retardation
Eczema
Blonde hair and blue eyes
Reduced melanin
Remove phenylalanine from the diet
65
Q

Describe MCAD deficiency and its treatment

A

Medium chain Acyl coA dehydrogenase deficiency
Common disorder of fatty acid oxidation
Sudden death
Beta oxidation cannot occur so fasting an hypoglycaemia is dangerous
adjust caloric intake and avoid fasting

66
Q

Compare somatic to germline mutations

A

somatic - occurs in a single body cell and cannot be inherited
gremlin - occurs in the gametes and can be inherited

67
Q

Give examples of types of mutations

A 
Aneuploidy
Translocation
chromosome:
Macro-deletions
Macro-insertions
gene:
Large insertion
Large or deletions

Point mutation

68
Q

What are the hallmarks of cancer

A 
Dysregulated growth
Evasion of apoptosis
Limitless replication
Sustained angiogenesis
Invasion/ metastasis
Genome instability and mutation (disordered growth, disordered death, disordered behaviour)
69
Q

Explain what a polyclonal disease is

A

Cancer is polyclonal

Many clones of varied genetically distinct cells

70
Q

Compare driver to passenger mutation

A

driver - The 1st key mutation
Can cause a normal cell to become a cancer cell

passenger - mutations that don’t contribute to the development of cancer but have occurred during cancer growth

71
Q

What are the 2 main classes of cancer causing genes

A

proto-oncogenes

tumour suppressors

72
Q

What is Knudson’s 2 hit hypothesis

A

Most TS genes require damage to both alleles to make the cell cancerous
Hit 1 reduces transcript/protein levels but there is no phenotypic affect
hit 2 causes a total loss of transcription (usually a deletion) and causes malignant potential

73
Q

Give an example of Knudson’s two hit hypothesis in practice

A

Retinoblastoma
When TF E2F is bound it is not functional
Mutated RB does not bind
RB phosphorylated by cyclin CDK, releasing E2F
Genes transcribed to cause pro-growth signals

Familial - child born with 1 mutation, second is somatic

Sporadic - one somatic mutation acquired, second somatic mutation in the same cell

74
Q

What is an SNP

A

Single nucleotide polymorphism where the base on the genes of different chromosomes are different
DNA cannot be sequenced without an SNP

75
Q

How can SNPs be used to guess the cause of disease

A

1st hit = SNP
2nd hit = Large deletion
If there is not SNP then it is likely there was a large deletion

76
Q

What percentage of breast cancers are caused by germline mutation and of what genes

A

2.4%
BRCA1 or BRCA2
BRCA2 predisposes to breast cancer in men

77
Q

Describe breast cancer as mutations

A

Hit 1 is inherited
hit 2 may not always occur
BRCA genes are TS genes that repair DNA by homologous recombination which cannot happen with mutation

78
Q

Which defects in cell division or DNA repair influence the risk of familial colorectal cancer

A

Familial adenomatous polyposis

Lynch syndrome

79
Q

Describe familial adenomatous polyposis

A

Thousands of intestinal polyps which contribute risk to colorectal cancer
Caused by the APC gene on chromosome 6
Autosomal dominant

80
Q

Describe HNPCC

A

hereditary non polyposis colorectal cancer
Most common inherited form
mutation of MLH1 or MSH2 (DNA repair genes)

81
Q

Describe oncogenes and tumour suppressors

A

Proto-oncogenes promote growth and proliferation in cells and those that are in overdrive are oncogenes.
Signalling cascades and mitogenic pathway activation

TS genes regulate cell division, DNA damage, apoptosis and DNA repair
mutations cause loss of function and faulty cell division

82
Q

Describe chronic myeloid leukaemia

A

Clonal myeloproliferative disorder => overproduction of mature granulocytes
Middle ages/elderly
3 phases: chronic (benign), accelerated (omnious), blast crisis (acute leukaemic, invariably fatal)
Philadelphia chromosome is found in >90% produces a new tyrosine kinase

83
Q

What are the indications of testing

A 
Nuchal scan
Mid-trimester
Previous pregnancies with DS or CF
Parents are carriers of chromosome rearrangement or genetic condition
FH of genetic condition
84
Q

Describe the nuchal scan

A

Looks at the thickness of the fluid at the back of the fetal neck
> 3mm indicates a chromosomal abnormality
Not a diagnostic test
Could be Down’s, Edwards, Patau or cardiac

85
Q

What is the combined test for Down’s

A

Combined test =levels of the hormone free beta-hCG +protein PAPP-A
High hCG and Low levels of PAPP-A.

86
Q

Describe the mid-trimester scan

A

20 weeks
dates the pregnancy
Diagnose miscarriage or fatal anomalies

87
Q

What are the reproductive options available

A

Planning prenatal testing
Facilitating decision making
Seeing patients in clinic following diagnosis in utero
Arrange termination if necessary
Discuss recurrence risks and plans for future pregnancies
Taking into account: previous experiences, family situation, personal beliefs, psychosocial situation, miscarriage risk with genetic risk

88
Q

What types of scanning are done in pre-natal testing

A

ultrasound - early scan, nuchal, anomalies in hands, feet, face, lip
MRI at 20 weeks

89
Q

Describe non-invasive pre-natal testing

A

Maternal serum screening = testing serum markers in the blood for trisomy 21 or 18 + nuchal measurement
cell-free fetal DNA = analysing DNA fragments in the maternal plasma during pregnancy. baby at 9 weeks. Only 10-20% from the placenta
ultrasound

90
Q

What are the disadvantages of non-invasive testing

A

Both not as useful for multiple pregnancies

non-invasive is harder with a greater BMI

91
Q

Describe Amniocentesis

A

Invasive
16 weeks onwards
Sample the amniotic fluid which contains fetal cells
1% miscarriage risk, infection, Rh sensitisation

92
Q

Define heritability

A

The study of genetic contribution to increased risk of disease
Studies usually use mono and dizygotic twins

93
Q

Why may estimates on heritability vary

A

different populations
different ages
baseline risk of disease in population
sampling variance

94
Q

What is GWAS

A

genome wide association studies that studies SNPs

95
Q

What is the copy number variant

A

Repeated code
Deletions, duplications, insertions that increase polygenic disease risk
Found in obeisty

96
Q

What are the types of obesity

A

Monogenic - dominant or recessive single gene disorder
Common - general population
Syndromic - e.g. Prader Willis

97
Q

What is leptin

A

Hormone made by adipocytes inwards white adipose tissue which circulates in proportion to the amount of adipose tissue
Inhibits appetite via the hypothalamus
High with high fat

98
Q

What are the symptoms of monogenic leptin deficiency

A 
hunger
obesity
no puberty
poor growth
Low thyroid
99
Q

Give examples of genes that cause single gene obesity

A 
MC4R = dominant 
PCSK1 = recessive
POMC = recessive
MRAP2 = recessive
100
Q

How is obesity clinically management

A

Lifelong prevention
Lifestyle measures
Medication
bariatric (weight loss) surgery

101
Q

How is obesity diagnosed

A

PCR for diagnosis
Pre-implantation diagnosis for IVF embryos
Mitochondrial transfer (3 parent babies)

102
Q

What is Sanger sequencing

A

Amplifying the region of interest with nucleoside terminators
Genetic sequence of the region of interest

103
Q

What is Next generation sequence

A

Fragmentation, sequencing and mapping of reads

sequence of the genome/transcriptome

104
Q

What are the advantages and disadvantages of Sanger sequencing

A

quick
gives sequence

cannot multiplex
Limited to 2000bp

105
Q

What are the advantages and disadvantages of next generations sequencing

A

Massively multiplex
Multiple different libraries

Cost
Time
Read-depth
Data overload
Library bias
106
Q

Describe chorionic villus sampling

A 
Invasive
11-14 weeks
1-2% miscarriage risk
Sample of chorionic villi part of developing placenta (same DNA as the foetus)
Ealier result than amniocentesis

MCD (13 decks)

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