mixed SAQs Flashcards

1
Q

a) Name three file types used in an NGS analysis pipeline (3)

A

3 from: FASTQ
BAM or SAM or CRAM
VCF
BED

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

b) For each of these file types describe their contents and use. (6) fastq, bam, vcf, bed

A

FASTQ- Text file containing sequence reads and associated quality information

Standard format containing all reads from sequencing. Can be analysed to generate quality metrics, and used as input for read alignment tools.

BAM or SAM or CRAM- aligned/mapped reads and associated quality information

Output of read alignment. Can be analysed to generate quality metrics.

VCF - data lines containing information about a position in the genome, usually variants. May also include annotations

Output of variant calling. Annotations may be added prior to variant filtering and analysis.

BED - Genomic regions (chromosome, start and end)

Used to define the regions of interest for the assay.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

c) NGS analysis often involves aligning short DNA sequences (reads) to a reference genome. Give two reasons why a read might not align correctly to the reference. (2)

A

Two from:
Read maps to multiple locations in the reference genome (e.g. pseudogene)
Reference genome is incomplete so sequence is missing (e.g. centromeric regions)
Errors introduced during sequencing
Variants in the sequence compared to reference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

d) Reads that do not map uniquely to the reference genome (i.e. map to more than one location) are given a mapping score of 0 and may be excluded from downstream analysis. Explain possible reasons for non-unique mapping and what impact this might have on the clinical use of NGS. (3)

A

Duplicated regions of the genome (segmental duplications, pseudogenes) can result in the same sequence being present in 2 or more locations in the genome. NGS sequence reads that map to these duplicated regions will not have unique mapping and therefore may be removed from downstream analyses. If clinically relevant genes have a pseudogene it may be difficult to get sufficient coverage of the gene for variant calling. Alternatively, called variants may be in the pseudogene and not the gene itself. An alternate method may be required to confirm results in these genes such as long range PCR.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

e) Give an example of a gene and an associated genetic disorder that might be difficult to analyse by NGS because reads do not map uniquely to the reference (2)

A

Possible examples: SMN1 and Spinal Muscular Atrophy or PMS2 and Lynch Syndrome
(both have pseudogenes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Briefly describe paired-end sequencing and explain the advantages of paired-end over single-end sequencing for detecting variants associated with human disease. (4)

A

paired-end sequencing- Sequence both ends of the DNA fragment.
Paired-end sequencing can be useful for detecting structural variants (deletions, insertions or inversions)- read pairs mapping to different locations in the genome give information about the position of that sequence. This is not possible with single-end sequencing. Structural variants are a common cause of genetic variation and therefore genetic disease.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the underlying genetic cause of fragile x?

A

FRAX is an X-linked recessive triplet repeat expansion disorder caused by a CGG
repeat expansion within the 5’ UTR of the FMR1 gene on the X-chromosome. When
the triplet repeat expands beyond a threshold (>200 repeats), this causes
hypermethylation of the FMR1 promotor and silencing of the gene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe PCR for sizing?

A

The sizing PCR is a standard PCR with a F & R primer (one of which is fluorescently
labelled). Products are separated by capillary electrophoresis and sized against a
molecular ladder.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

describe TP-PCR

A

TP-PCR uses F & R primers (again one of which is fluorescently labelled) and also a third
primer which is specific to the triplet repeat. The third primer is added in a limited
manner so that it is exhausted in early PCR rounds. This is to avoid preferential
amplification of smaller alleles. The products from the TP-PCR are also separated by
capillary electrophoresis and sized. A full expansion allele gives a classic ‘ski-slope’
pattern which tails off towards the larger end of the repeat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

a) List three differences between the nuclear and mitochondrial genomes

A

The mitochondrial genome is a fraction of the size of the nuclear genome (~16.5kb)
The mitochondrial genome is a small circular molecule
Mitochondrial DNA is maternally-inherited only.
Mitochondrial has no introns and very few genes ~37

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the inheritance patterns associated with mitochondrial disease

A

Mitochondrial disease can be caused by pathogenic variants in the mtDNA itself (maternally
inherited only) or by pathogenic variants in nuclear genes involved in mitochondrial DNA
maintenance which can be autosomal dominant or recessive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define the term heteroplasmy and homoplasmy and mitochondrial bottleneck

A

Heteroplasmy – where two or more different variants of mtDNA exist within a cell

Homoplasmy – where all copies of the mtDNA are identical within a cell.

Mitochondrial bottleneck – a random shift of mtDNA mutational load between generations
(and even siblings) due to unequal transfer of mtDNA molecules during oogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe 3 considerations for interpretation of pathogenicity unique to mtDNA variants

A

There are currently no mitochondrial DNA specific guidelines for interpreting variants.
Inheritance pattern (maternal or nuclear)
Population databases used (Mitomap instead of gnomAD for example)

check heter/homoplasmy levels in proband vs mum – if homoplasmic variant inherited from homoplasmic unaffected mum its unlikely to be disease- causing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Clinicians have referred an adult presenting with optic neuropathy to the highly specialised mitochondrial diagnostic service. Describe the appropriate testing pathway and any relevant candidate genes and variants for targeted analysis

A

Optic neuropathy is a generic term and can be caused by pathogenic variants in mtDNA
(such as Leber’s hereditary optic neuropathy (LHON)) or nuclear DNA. There are common
LHON variants which can be easily identified/excluded such as m.11778G>A (MT-ND4),
m.3460G>A (MT-ND1) and m.14484T>C (MT-ND6).

If these are negative, full gene screens can commence for each of the above three
mentioned genes.

f full gene screens are negative, a nuclear based eye panel may be appropriate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Name the gene responsible for encoding mitochondrial DNA polymerase

A

POLG (polymerase gamma)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is copy number variation?

A

A loss or gain of a region of the genome (could be single exon, multi-exon, whole
gene or multiple genes).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What types of genetic/genome abnormalities can oligoarray NOT detect

A

Uniparental disomy
Balanced translocations
Triploidy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the differences between a SNP and oligo array?

A

An oligo array uses the patient and a sex-matched control sample which compete for
hybridisation to the probes on the array slide. The patient and the control DNAs are
labelled in different fluorescence and the captured image is converted to show if the
patient has a gain or loss compared to the control sample.

SNP arrays use thousands of known SNP positions across the genome and each SNP
is genotyped into AA homozygotes, BB homozygotes and AB and BA heterozygotes.
The patient is genotyped at each SNP position which is used to calculate the ratio of
AA, BB, AB and BA SNPs at each position and determine the copy number by the
ratio of heterozygous and homozygous SNPs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Briefly explain the use of the 3 resources/databases that you would use to aid interpretation of the clinical significance of a copy number change.

A

Database of Genomic Variation (DGV) – the DGV ‘gold standard’ track provides
information on the frequency of your copy number variant in the population. For
example, a CNV with a frequency of 0.80% in a population of 17,000 would be too
high to be disease causing.

ClinGen – This resource provides information on dosage pathogenicity and gives a
haploinsufficiency score and a triplosensitivity score for each gene in the CNV call.
For example a haploinsufficiency score of 3 would automatically make the CNV
pathogenic.

Decipher – Large database with national patient cohort. This can be used to
determine if your CNV has been seen before, the phenotype of the patient/s with
this CNV, the reporting laboratory and any overlapping features with similar
patients.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Briefly describe a known microdeletion syndrome region involving chromosome 16; include location, key gene(s) involved and provide two clinical features.

A

16p11.2 microdeletion syndrome which includes the TBX6 gene. Patients with this
disorder have intellectual disability, developmental delay and some also have autistic
behaviours.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Many newly described microdeletion or microduplication syndromes detected by
microarray are subject to reduced penetrance and variable expressivity. Define these
terms.

A

Reduced penetrance – Not all people with the genetic change will display the
features associated with that disorder.

Variable expressivity – The phenotype of the disorder is variable amongst
individuals, even those within the same family.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

a) Give 3 clinical features of Prader Willi syndrome.

A

Intellectual disability
Obesity
Hypotonia in infancy
Hyperphagia
Overgrowth
strabismus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Give 3 clinical features of Angelman syndrome.

A

Seizures
Characteristic hand movements
Inappropriate laughter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

AS PWAS Define the chromosomal region associated with these conditions.

A

15q11.2-15q13

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

List the different mechanisms that may result in Angelman syndrome together with
their recurrence risk for future pregnancies.

A

Paternal chromosome 15 UPD – <1-2%
Maternal deletion of the 15q11.2-q13 region (likely de novo, low recurrence unless
germline mosaicism)
UBE3A pathogenic variant – 50%
Imprinting control centre deletion (up to 50% recurrence)
Imprinting control centre defect (<1%) (

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Describe two testing methods by which a Prader-Willi case may be genetically
confirmed.

A

Methylation-specific PCR
Methylation-specific MLPA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Name 3 other imprinting disorders.

A

Beckwith-Wiedemann syndrome
Silver-Russell syndrome
Temple syndrome
Transient neonatal diabetes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

A 5 month old infant girl presents with a diagnosis of B-lineage Acute Lymphoblastic
Leukaemia (ALL)

Describe the priority setting and testing strategy for this sample?

A

This would be classed as an urgent referral

FISH for the common t(4;11) (MLL gene and AF4) translocation found in infant ALL – if
negative proceed to ETV6/RUNX1 FISH which will also detect iAMP21 and BCR/ABL1
FISH
As BCR-ABL1, ETV6-RUNX1, iAMP21 and MLL rearrangements are thought
to be mutually exclusive, if one abnormality is detected it is not mandatory to
exclude others.
If there is normal/failed result, ALL BPGs suggest additional FISH to detect hidden
hyper/hypodiploidy.
Extract DNA for SNP array
RNA extraction for fusion panel analysis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

5 month old infant girl presents with a diagnosis of B-lineage Acute Lymphoblastic
Leukaemia (ALL)

What would be the most common/likely chromosome abnormality detected in this
patient and give the prognosis. Include ISCN for abnormality and name the genes
involved.

A

46,XX,t(4;11)(q21;q23) – poor prognosis, MLL gene and AF4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

c) The patient is negative for the above abnormality. The ETV6-RUNX1 dual fusion probe for this patient shows two fusion, one red, and one green signal pattern (2F1R1G). What does this pattern suggest the patient carries and what prognosis does it confer?

A

They are positive for the ETV6/RUNX1 fusion which confers a favourable prognosis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

If the ETV6-RUNX1 dual fusion FISH probe showed a loss of the green ETV6 signal
(2F1R0G), what would this indicate loss of and how would this effect the prognosis?

A

Loss of the normal chromosome 12 – prognosis does not change.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

e) Give two other chromosomal abnormalities seen in ALL that could be detected using the ETV6-RUNX1 probe other than the rearrangement in part C).

A

Loss of the red RUNX1 signal would indicate loss of the normal chromosome 21

Amplification of the red signal would indicate iAMP 21 (intrachromosomal amplification of chromosome 21)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

describe the process of QF-PCR?

A

amplification of STRs on chromosomes of interest used to determine copy number
● STRs (short tandem repeats or microsatellites) are a pattern of 2 - 6 bp that are repeated directly adjacent to each other.
● STRs are known highly polymorphic markers; a patient is therefore likely to have different numbers of repeat units on each allele.
- 4 markers for each chromosome of interest and sex chromosome markers if referral indicates sex chromosome abnormality eg. AMEL, SRY and DXYS218(Xp) and X22
- quantitative pcr - extracted DNA added to fluorescent primer multiplex and pcr. The reaction must be quantitative to detect copy number, therefore the PCR is stopped while in exponential phase to detect copy number -“ During the exponential phase of the reaction, the amount of product is directly proportional to amount of template “
- rapid, cheap, small quantities of DNA needed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

following a positive qf-PCR result, what other tests would you offer?

A
  • sample identity must be confirmed prior to reporting (N.B. by a repeat test of the original sample or genotype comparison with a maternal blood sample
  • karyotype to visualize abnormal rearrangements
  • normal results based on a single marker should be confirmed by a second method, e.g. karyotype or FISH.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what are Characteristics of cffDNA?

A

-placenta - shed highly fragmented DNA into the maternal circulation during normal apoptosis
the total cell free DNA in maternal plasma that comes from the placenta (up to 20%)
- reliably detected from 7 weeks
- increases with increasing gestation
- rapidly cleared from circulation within an hour after delivery
- fetal DNA is shorter -approximately 200bp for fetal fragments and larger for maternal fragments.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

how do you calculate fetal fraction?

A

dividing the amount of reads mapped to chromosome Y by the total amount of reads mapped to autosomal chromosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

define heteroplasmy

A

which two or more mtDNA variants exist within the same cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

what is mitochondrial donation ?

A

ooctye donation or nuclear transfer where the nuclear genome from the oocyte or embryo of an affected woman is transplanted into a donor enucleated oocyte or embryo with healthy mt.

nuclear DNA can be transferred between unfertilised oocytes using polar body transfer or maternal spindle transfer or between fertilised zygotes using pronuclear transfer

39
Q

what genes/mutations are involved in Leigh syndrome?

A

MT-ATP6 m.8993T>C (also MT-ND1, 4 and 6)
Encephalopathy, lactic acidosis

40
Q

MDS - what are common chromosomal abnormalities as well as prognosis?

A

-5q deletion (15% of cases) - good prognosis if isolated finding. low risk of transforming to AML. TP53 mutation testing recommended in WHO as presence of mutation and del(5q) predicts poor response to lenolidomide
-monosomy 7 - poor prognosis (more common in therapy-related MDS)
- trisomy 8- intermediate
- complex (3 or more abnormalities often TP53 locus) 90% of therapy related-MDS - poor prognosis

41
Q

what do the new WHO 2016 leukaemia guidelines contain updates for?

A

new clinical, prognostic, morphologic, immunophenotypic, and genetic data that have emerged since the last edition

morphology = blood and marrow smears morphologically examined using Giemsa stain. blast count >20%

immunophenotyping = examine expression of cell-surface markers using flow-cytometry

cytogenetics - chromosomal abnormalities in 55% of adult AML cases

molecular genetics- screening for mutations in
a) NPM1, CEBPA, and RUNX1 genes
b) FLT3 - ITD, WT/M ratio and D835 and I836 tyrosine kinase domain mutations
3)TP53 and ASXL1 - poor prognosis

RT-PCR for recurrent gene-fusions. initiated when cytogenetics fails. following identification of a translocation by karyotype and for cryptic gene fusions where cytogenetic abnormality not present. also used to monitor MRD.

42
Q

give two abnormalities in AML (include breakpoints) associated with good prognosis?

A

t(8;21)(q22;q22) - RUNX1T1-RUNX1
inv(16)(p13q22)
t(15;17)(q24.1;q21.2) - PML- RARA

43
Q

give two abnormalities in AML (include breakpoints) associated with poor prognosis?

A

t(9;22)(q34;q11)
5q abnormalities

44
Q

CML – what is the common resistant mutation and treatment?

A
  • point mutation in BCR-ABL kinase domain
  • Second and third generation TKIs e.g. Nilotinib, Dasatinib and Ponatinib have been developed to try to overcome this TKI resistance

T315I mutation was the most frequently detected

45
Q

what is the most common ALL abnormality in 1-25 years?

A

t(12;21) ETV6-RUNX1 t(12;21)(p13;q22)

good prognosis

46
Q

what is the most common (50%) ALL abnormality in infants <1 year?

A

MLL translocation t(4;11)(q21;q23)

poor prognosis

47
Q

after MLL rearrangements and ETV6-RUNX1, what is the 3rd-line test for B-ALL in < 1 years?

A

1) t(9;22)(q34;q11) BCR-ABL1 rearrangement (4%)

poor prognosis

48
Q

what is the most common rearrangement in T-ALL?

A

TCR (T-cell receptor) rearrangements - usually placed next to transcription factors
unknown prognosis

49
Q

what is the most significant genetic prognostic factors for adult ALL?

A

t(9;22)(q34;q11) BCR-ABL1 Philadelphia chromosome - 30% of adult ALL cases

poor prognosis

50
Q

what is the second-line test in adult B-ALL? what is the prognosis?

A

t(4;11)(q21;q23)
MLL (chr11) AF4(chr4)
poor prognosis

51
Q

other than (4;11)(q21;q23) MLL ; AF4 what other common rearrangements involving MLL are found in ALL?

A

o t(9;11)
o t(11;19)

52
Q

other than BCR:ABL1, MLL rearrangements and ETV6-RUNX1 what other common rearrangements are found in ALL?

A
  • high hyperdiploidy (51-56 chromosomes) - good prognosis
  • hypodiploidy <44 chromosomes
  • TCF3 rearrangements
  • IGH rearrangements
  • Dic (9;12)
  • Dic(9;20)
    Abn/del(9p)
53
Q

what files do you need to have ready for a new start up?

A

induction plan - Who will they need to meet, what training will they need
Personal Development Plan - forms part of probation
Security - Request for ID/Access Card form
request a basic IT account
Mandatory training
Contract
New Starter form - PAY

54
Q

SMA result homozygous of the common mutation, and one parent is a carrier and the other is negative, how do you explain that?

A

4% of population have two copies of SMN1 on one chromosome
non paternity
sample mixup
de novo
allele dropout - polymorphism

55
Q

PWS/SMA hypotonia question, name other types of dystrophies?

A

myotonic dystrophy

56
Q

PWS/SMA name other types of dystrophies and genes involved?

A

myotonic dystrophy - DMPK & ZNF9 (DM2)
FSHD - AD contraction of D4Z4 repeats (contains DUX4 gene)
CMD - TTN LMNA MYH7

DMD/BMD - DMD

57
Q

Expansion repeats (CAG repeats polyQ, give three examples, other than spinocerebral ataxias).

A
  1. HD - HTT gene
  2. SBMA - XLR - AR gene (also causes androgen insensitivity syndrome)
  3. dentatorubral-pallidoluysian atrophy (DRPLA) - CAG expansion in ATN1 gene

All exonic! GOF - CAG repeat expansions result in polyglutamine aggregates

58
Q

What are the repeat sizes with normal, intermediate and full mutation for HD and Frax.

A

FRAX
N up to 45
46-58 int
premutation 59-200
mutation >200

HD
6-26 N
27-35 int
36-39 red pen
>39 complete penetrance

59
Q

what is anticipation?

A

trinucleotide repeat expansions in successive generations in which the signs and symptoms of some genetic conditions tend to become more severe, more frequent or occur at an earlier age

60
Q

what is the most common EGFR mutation in NSCLC lung cancer? what is the most common resistant mutation?

A

18bp in-frame deletion in exon 19 (c.2240_2257del) and a common point mutation in exon 21 (p.L858R) (90%). GOF activating mutations.

p.T790M mutation is the most common resistant mutation and is found in ~50% of patients that develop acquired resistance to tyrosine kinase inhibitors

61
Q

Define SNV and give other examples of mutations

A

A DNA sequence variation that occurs when a single nucleotide (adenine, thymine, cytosine, or guanine) in the genome sequence is altered

substitution
deletion
insertion
duplication
inversion
delins

62
Q

what is evidence for variant pathogenicity?

A

null variant
Same amino acid change as a previously established (likely) pathogenic variant
de novo
functional studies
prevalence of the variant in affected individuals is significantly increased compared with the prevalence in controls
mutation hotspot
absent from controls
For recessive disorders, detected in trans with a (likely) pathogenic variant
Protein length changes as a result of in-frame deletions/insertions in a non-repeat region
missense change at an amino acid residue where a different missense change determined to be likely pathogenic has been seen before
segregation
Missense variant in a gene that has a low rate of benign missense variation
Multiple lines of computational evidence support a deleterious effect - (conservation, evolutionary, splicing impact
highly specific phenotype
reputable source

63
Q

define validation?

A

validation = ‘Confirmation, through the provision of objective evidence, that the requirements for a specific intended use or application have been fulfilled’ (doing correct test)

Validation is required when there is no suitable performance specification available and the performance characteristics of the test need to be defined.

with the almost complete absence of reference tests or certified reference materials, the reference should be the most reliable diagnostic method available

64
Q

define verification?

A

verification = ‘Confirmation, through the provision of objective evidence, that specified requirements have been fulfilled’ (doing test correctly)’

If a suitable performance specification is available, it is necessary to check that the new test meets this specification within the laboratory (verification).

Verification is also appropriate when a new test is introduced that uses a well-established method within the lab.

65
Q

what is positive predictive value?

A

he likelihood that an individual with a positive test result truly has the particular gene and/or disease in question

true positives/true positives + false positives

66
Q

what is negative predictive value?

A

he likelihood that an individual with a negative test result is truly unaffected and/or does not have the particular gene mutation in question

true negatives/true negs + false negs

67
Q

why might there be elevated neonatal IRT apart from CF?

A

neonatal stress (low Apgars), respiratory distress, hypoglycaemia, or serious congenital abnormalities such as trisomies 13 and 18

PPV is low for IRT

68
Q

what is the CF testing pathway for a newborn with high IRT on first 5 day test?

A

screen 4 most common variants accounting for 80% of variants seen in the UK population. If a single variant detected or two variants (immediate referral to a CF specialist), screen for all variants.

2nd IRT on day 28 if first is raised. If no mutation identified but still high > CF suspected. If one mutation detected but still high > CF suspected. If one mutation detected and IRT normal on 2nd test = probable carrier.

69
Q

combined test which two markers included in that test?

A

free beta human chorionic gonadotropin (bhCG) and pregnancy associated plasma protein-A (PAPP-A)

70
Q

what DS screening markers first and second trimester?

A

1st trimester
NT - detects 60% of cases
serum markers PAPP-A and free beta
absent nasal bone
doppler evaluation for regurgitated blood flow
limb abnormalities - short long bones

2nd trimester
18 week scan:
cardiac defects
duodenal atresia- closure in the first part of their small intestine

soft:
echogenic bowel
sandal gap

71
Q

DMD – treatments available?

A
  • stop codon readthrough eg. translana. 15% of patients have PTC. Tretments allows alternative amino acids to be inserted at the site of the mutated stop codon & results in dystophin expression at 10-20% providing some function
  • exon skipping eg. exondys51 (80% of patients in theory). Interferes with splicing skipping the specific exon in DMD pre-mRNA to restore open reading frame and allow expression of shorter but functional protein
72
Q

how are CML patients tested in the lab?

A

-G-banding analysis on blood or marrow of 10 cells and BCR/ABL1 FISH test for cryptic or variant translocations
-It is useful to carry out molecular analysis to confirm the presence of BCR::ABL1 gene rearrangement (TR-PCR) and to determine the nature of the rearrangement for future Minimal Residual Disease (MRD) analysis.
-Patients with a positive result will benefit from treatment with Imatinib
- also scan for secondary abnormalities including +Ph, +8, +19, +21, -Y, i(17q).

73
Q

describe the gene structure during transcription/translation

A

Transcription (DNA > mRNA)

Gene = Promoter (proximal and core) > 5’UTR> start codon (open reading frame) to stop codon> 3’UTR

Promoter is 5’ and consists of core and proximal (most 5’). Core promoter contains RNA polymerase binding site, TATA box (transcription factors bind) and proximal contains TF binding sites.

5’ UTR spans TSS to start codon. Binds ribosome.
3’ UTR immediately follows stop codon. contains terminator sequence (endpoint for transcription where RNA polymerase released), regulatory regions and polyadenylation signal which directs addition and cleavage of polyA tail to end of mRNA transcript (important for stabulity and nuclear export)

RNA is complimentary to DNA. undergoes splicing to remove introns and exons are joined. 5’ capping and 3’poly-A tail added

Translation (mRNA > protein)

mRNA consists of 5’ cap, 5’UTR, coding segment, 3’UTR and polyA signal

74
Q

Mention an example where the testing of a gene would be important for a particular drug dosage

A

DPYD metabolizes 5FU chemo drug
-DPYD variants may cause poor metabolism and so dose-management is critical to prevent toxicity. -heterozygotes usually asymptomatic but homozygotes may have epilepsy and motor dysfunction.
- 4 known variants affect protein function and lead to increased toxicity
- the 4 variants are given different activity values
- depending on whether hom, het or compound het the DPD activity is classified into normal, intermediate or poor metabolisers
- intermediate metabolisers should reduce dose by 50%. dose is then adjusted depending on toxicity
- NHS england provide this service to all patients prior to 5FU chemo

  • warfarin prevents clotting in thromboembolism
  • metabolised by CYP2C9
  • polymorphisms in CYP2C9 contribute to variability in dose requirement (15% variation in warfarin response)
  • overdosing leads to excessive bleeding
  • limited genotyping in the UK
75
Q

what would you include in a VUS report?

A
  • Only report if hot/warm VUS which high level of supporting evidence and where additional evidence might upgrade eg. parents, further testing (imaging/biochem/muscle), mRNA in recommended action and how it might change classification
  • treatment trials if available
  • ‘No clearly pathogenic sequence variants were detected.
  • Diagnosis not confirmed
  • clinical significance of the unclassified variant is uncertain6 and presymptomatic testing in unaffected family members is not recommended.
76
Q

AML translocation (8;21) - what would you write in the report, mention 2x other leukaemia translocations that involve 21.

A

Good prognosis
proportion of neoplastic cells in the sample
testing method
result
interpretation
clinical trials
notes and references

ALL: t(12;21)(p13;q22) ETV6-RUNX1 good prognosis
ALL: iAMP(21) - poor prognosis
MDS/AML t(3;21)(q26. 2;q22) - Therapy-Related Disease Associated With Poor Outcome

77
Q

what tests/techniques can you do with AML

A

karyotype + FISH
FISH for del(5q), del(7q) and monosomy 7 and 17p (TP53) will detect myelodysplastic related changes
RT-PCR to characterise breakpoints and monitoring
NGS panel testing for the identification of driver variants within RUNX1, TP53, FLT3 is mandatory (may be germline origin) - skin biopsy.

78
Q

molar pregnancy - mechanisms, tests, features, how would you treat the mother

A

complete mole = Only paternal chromosomes; diploid. empty egg and two sperm or duplicated sperm.

symptoms = hypertension, oedema (fluid) and vaginal bleeding, increased uterus size, risk of trophoblastic disease

partial hydatidiform mole : Double paternal contribution i.e. two paternal sets and one maternal set of chromosomes eg. 69, XXY, 69,XXX or 69,XYY - fertilisation of a normal egg by 2 sperm (dispermy), duplicated or diploid sperm

IUGR, neural tube defects, Oligohydramnios (too little fluid), Large placenta (cystic), later on - syndactyly (webbed fingers or toes) and hydrocephaly (fluid on brain)

• Blood tests will show very high levels of hCG
- ultrasound scan - the mole resembles a bunch of grapes
- • A definitive diagnosis requires histopathological examination

treatments: Suction evacuation , monitor hCG levels, • Chemotherapy recommended if Metastases identified or rising levels of hCG

79
Q

array CNV investigation - how would you evaluate the gene content. databases you would look at. what is a high haploinsufficiency score ?

A

CNV genomic content: size,overlap with established triplosensitive (TS), haploinsufficient (HI) or benign genes/genomic regions; gene number and content population frequency, evaluation of literature, public databases, internal lab data; inheritance pattern/family history for patient being studied

  • multiple unrelated patients with a similar CNV and a consistent phenotype (more likely pathogenic)
  • de novo supports pathogenicity. Additional weight is given if the phenotype is highly specific and relatively unique to the gene/genomic region.
  • Segregation amongst similarly affected family members supports pathogenicity
    • Non-segregations EXCEPT incomplete penetrance, phenocopies (variation caused by environment that resembles a genetic variation), accurate phenotyping of family members, age of onset and inheritance pattern
  • for a CNV identified in recessive gene - look for SNV on other allele

loss of one allele resulting in a single normal allele at a particular locus is inadequate for normal function resulting in a phenotype. Regions of copy number loss containing established HI genes are more likely to be pathogenic.
HI info available on ClinGen, decipher, knockout mouse models, literature, ClinVar, HGMD, OMIM
pLI available on GnoMad

80
Q

Beckwith Wiedemann - clinical features (mention 4), genes involved, other tests you could do

A
  • overgrowth, macroglossia, hypoglycaemia, Wilms tumour
  • H19, IGF2 (ICR1) and KCNQ1 ,
    KCNQ1OT1, ICR2 and CDKN1C (ICR2)
  • CDKN1C sanger
    • array CGH, SNP array, karyotype, FISH, MLPA, MS-MLPA
81
Q

FFPE sample - issues and how would you overcome. examples of tests you can do from FFPE samples?

A
  • variable quality depending on size of resection, amount of time in formalin or whether recalcified (bone samples - unsuitable for testing)
  • extracted DNA is fragmented
  • more PCR artefacts due to deamination of cytosine>uracil - results in C>T/G>A transition sequencing artefacts
  • low tumour %
  • need specific technologies to detect low-level mutation
  • Tumour heterogeneity - mutation may only be present in part of tumour
  • test failure due to poor quality/quantity
  • is labour intensive - hard to have fast TATs (eg. EGFR testing in Lung cancer up to 2 weeks)
  • lynch, breast solid, NSCLC
82
Q

|Cancer: genes associated with treatment in Lung, CRC, mention 2x genes you would test in Melanoma

A

inherited cutaneous malignant melanoma - CDKN2A or CDK4

EGFR mutation - Gefitinib if mutated
EGFR + KRAS - if WT cetuximab
BRAF - MEK inhibitor
Osimertinib 2nd line treatment can be given to EGFR+ and T790M EGFR inhibitor resistance lung cancers

83
Q

what is sensitivity?

A

Sensitivity is the ability of a test to correctly identify individuals who are affected by a disease, (the true positive rate)

True positives/true positives + false negatives

84
Q

what is specificity?

A

the ability of a test to correctly identify individuals who are not affected by a disease, (the true negative rate)

true negatives/true negatives + false positives

85
Q

FRAX - boy with 72 repeats. risks, implications to family. other than direct PCR what tests can you do in FRAX (mention 4).

A

FXTAS (50%) - over 60 years onset
- expansion to full mutation exclusive to females and usually if >90 repeats - risk to other family members

southern blot - detects all sizes and methylation but laborious, large amounts of DNA required, doesnt have the resolution to detect size

Amplidex - detects normal, premutation and full mutations +some detect methylation, AGG repeats but expensive as a first-line test

linkage - STR markers. may be useful in prenatal eg. if southern blot fails.

NGS - SNVs, deletions, duplications

86
Q

Williams, whole X mosaic del, PLS (Potocki-Lupski syndrome – chr 17p 11.2 dup) , DiGeorge, - mention relevant genes

A

williams 7q11.2 - ELN (Elastin)
PLS (Potocki-Lupski syndrome – chr 17p 11.2 dup retinoic acid inducible 1 (RAI1) gene
X chromosome - SHOX (Xp22) AR (Xq12) XIST (Xq13)
Di George 22q11.2 TBX1

87
Q

Xp deletion in a male - mention gene, other tests you could do, clinical symptoms?

A

SHOX - Xp22.33
short stature
Leri-Weill dyschondrosteosis (LWD) - short stature, scoliosis,

FISH, array, karyotype

88
Q

AZF deletion found and there were 2 X. and write the possible karyotype. possible explanation. mention gene examples involved in DSD.

A

47,XX,del(Y)(q11), 47,XX,+idic(Y)(q11.21) or 47,XX,+idic(Yp)? 47,XX,+r(Y) - breakpoint Yq11.2

formation of isochromosome
fusion of p arm to q arm

89
Q

mention 4 genes involved in DSD?

A

Male
SRY - 46,XX male Disorder of Sex Development (DSD).
SOX9 - gonadal dysgenesis
SF1- gonadal dysgenesis
WT1- gonadal dysgenesis

Female
WNT4
RSPO1
FOXL2

AR - androgen insensitivity
CYP21A2 - CAH

90
Q

X-linked condition about ornithine syndrome.
Define and give example of X-linked recessive, X-linked dominant, Autosomal dominant with reduced penetrance.

A

Xp11.4 OTC gene
lack of the OTC enzyme results in excessive accumulation of ammonia
Symptoms include vomiting, refusal to eat, progressive lethargy, and coma

X linked recessive = mutation in a gene on the X chromosome causes the phenotype to be always expressed in males and in females who are homozygous eg. DMD, OTC deficiency (more severe in males), SBMA

X linked dominant = In females a mutation in a gene on one of the X chromosomes is enough to cause the condition. Fragile X, rett syndrome

AD reduced penetrance = BRCA, HD

91
Q

cf in newborn screen- high IRT, 2 mutations, what further tests would you do and importance

A

test parents to confirm zygosity and provide risk (1/4) to future pregnancies
offer testing to other family members if appropriate

92
Q

BRCA question - synonymous variant at the end of the exon no effect on protein change and not reported anywhere. how would you classify, what would you do.

A

vus
splicing predictions?
recommend functional studies, RNA analysis, minigene assay

93
Q

what docs do you need ready for new starter?

A

induction plan - Who will they need to meet, what training will they need
Personal Development Plan - forms part of probation
Security - Request for ID/Access Card form
request for basic IT account
Mandatory training
Contract
New Starter form – PAY