Department of SGE NIMS Hyderabad 23-03-2009
description
Transcript of Department of SGE NIMS Hyderabad 23-03-2009
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A GENETIC AND EPIDEMIOLOGICAL STUDY OF HEREDITARY NON-
POLYPOSIS COLORECTAL CANCER IN COLORECTAL CARCINOMA PATIENTS PRESENTING TO A TERTIARY CARE
HOSPITAL
Department of SGENIMS Hyderabad
23-03-2009
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THIS STUDY IS BEING DONE IN COLLABORATION WITH
CENTER FOR DNA FINGERPRINTING AND DIAGNOSTICS(CDFD)
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Abbreviations
CRC colorectal carcinoma HNPCC Hereditary Non-polyposis
Colorectal Cancer APC adenomatous polyposis coli MSI micro satellite instability MMR mismatch repair PCR polymerase chain reaction
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Outline
Background Aim Materials Methods
DNA isolation Genomic Tumor
Microsatellite instability Immunohistochemistry for MMR genes PCR Sanger’s sequencing
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What is HNPCC(Lynch Syndrome)
Definition is based on demonstration of mutation in MMR genes
No clinical definition Amsterdam’s criteria helps in
clinically defining HNPCC
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Amsterdam II criteria:
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What is Amsterdam's criteria
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What are Bethesda guidelines
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Tests for HNPCC
Screening tests Confirmatory tests
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Background
Colorectal carcinoma in India is biologically a different disease compared to western population. Occurs in young age Rectal carcinoma constitutes half of the cases Incidence is less Majority of young CRC patients are sporadic Late presentation
No studies on CRC genetics from India No reported cases of HNPCC from India
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Background
90% of CRC in west occur after 50years
India 50-60% <50years
WHY?
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Background
In west 10% occur in young 30% of these are HNPCC
This stimulated us to study about HNPCC and colorectal carcinoma in our own population
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Vogelstein’s pathway
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Background
HNPCC is caused by MSI, the hallmark of HNPCC
MSI is caused by MMR genes mutation
MMR genes are also called caretaker genes
MMR gene mutation causes HNPCC
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Background
Bethesda guidelines are for MSI screening
It is likely that Bethesda guidelines are not useful in Indian population.
This hypothesis will be either proved or disproved by our study.
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Life time risk of cancer in HNPCC
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Primary objective
To study the incidence of HNPCC in CRC patients presenting to NIMS.
To study the mutations causing HNPCC
To identify any new mutation Study the usefulness of MSI & IHC in
diagnosing HNPCC To screen first degree relatives of
HNPCC patients for MMR mutation
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Secondary objective
To assess age distribution , sex distribution , site distribution of CRC
To assess pathologic characteristics of CRC
To assess stage of presentation
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INCLUSION CRITERIA
1. CRC, diagnosed in patients < 50 years2. Synchronous or metachronous CRC or
other tumors associated with HNPCC, regardless of age
3. CRC with of MSI-H or specific histology diagnosed < 60 years.
4. HNPCC related cancer <50yrs in 1 first degree relative
5. HNPCC associated tumor at any age in two first- or second-degree relatives
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Exclusion criteria
All patients with neoadjuvant CT/RT are excluded from study.
All patients who are HIV/HBsAg +ve. Patients with FAP
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Methods
DNA isolation Genomic Tumor
Microsatellite instability Immunohistochemistry for MMR genes PCR Sanger’s sequencing
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Case 1
24yr female with bleeding PR Sigmoid carcinomas at two
synchronous locations-T2N0M0 Left hemi-colectomy T2N0M0 x2 3 yrs later - multiple carcinomas Caecum –T3N0M0 Duodenum-T2N0M0 Jejunum –T2N0M0
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DNA isolation
Genomic DNA Blood – easy to isolate Normal tissue
Tumor DNA H&E stained 5micron slide Identify tumor cells Scrape the cells Isolate DNA
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DNA isolation from blood
3ml blood Potassium EDTA bottle Store at 40⁰ c Should not be frozen If frozen - should not be thawed Blood should not be stored for more
than 7 days because yield will come down
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DNA isolation from blood
Centrifuge blood after adding erythrocyte lysis buffer –30min
Centrifuge @10000 rpm for 10min Discard supernatant fluid WBC pellet Add proteinkinase , DDS Incubate at 37⁰ C for 12hours Purification of DNA
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DNA isolation from blood
Purification is a lengthy procedure WBC pellet is digested with
proteinkinase Intra cellular contents are released Repeated purification and
centrifugation Protein heaviest at bottom DNA next to protein Need careful extraction
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Once DNA is isolated it can be stored at -20⁰ c for a long time for many reactions
Genomic DNA is highly concentrated Should be very careful otherwise it
will contaminate other reactions
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PCR
First described in 1985, Nobel Prize for Kary Mullis in 1993
The technique was made possible by the discovery of Taq polymerase, the DNA polymerase that is used by the bacterium Thermus aquaticus, discovered in hot springs.
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PCR
The primary materials, or reagents, used in PCR are: DNA nucleotides, the building blocks for the
new DNA Template DNA, the DNA sequence that you
want to amplify Primers, single-stranded DNAs between 20 and
50 nucleotides long (oligonucleotides) that are complementary to a short region on either side of the template DNA
DNA polymerase, a heat stable enzyme that drives, or catalyzes, the synthesis of new DNA
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Sample tray and micropipettor. Each tray holds 96 samples
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PCR
The result is a dramatic amplification of a the DNA that exists between the primers.
The amount of amplification is 2 raised to the n power;
n represents the number of cycles that are performed.
After 20 cycles, this would give approximately 1 million fold amplification. After 40 cycles the amplification would be 1 x 1012
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STEP-1
Denaturation at around 94°C : During the denaturation, the double
strand melts open to single stranded DNA, all enzymatic reactions stop (for example the extension from a previous cycle).
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STEP-2
Annealing at around 54°C : Hydrogen bonds are constantly
formed and broken between the single stranded primer and the single stranded template. If the primers exactly fit the template, the hydrogen bonds are so strong that the primer stays attached
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STEP-3
Extension at around 72°C : The bases (complementary to the
template) are coupled to the primer on the 3' side (the polymerase adds dNTP's from 5' to 3', reading the template from 3' to 5' side, bases are added complementary to the template)
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THERMOCYCLER
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Sitamahalakshmi
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AGAROSE GEL ELECTROPHORESIS
A method used toseparate macromoleculeslike proteins and nucleicacids (ie DNA/RNA) basedon their size and electriccharge
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Sequencing
“Sequencing” means finding the order of nucleotides on a piece of DNA .
Nucleotide order determines Amino acid order, and by extension, protein structure and function (proteomics)
An alteration in a DNA sequence can lead to an altered or non functional protein, and hence to a harmful effect
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Sequencing
Historically there are two main methods of DNA sequencing:
Maxam & Gilbert, using chemical sequencing
Sanger, using dideoxynucleotides.
Modern sequencing equipment uses the principles of the Sanger technique.
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The Sanger Technique
Uses dideoxynucleotides (dideoxyadenine, dideoxyguanine, etc)
These are molecules that resemble normal nucleotides but lack the normal -OH group.
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Because they lack the -OH (which allows nucleotides to join a growing DNA strand), replication stops.
Normally, this wouldbe where another phosphateIs attached, but with no -OHgroup, a bond can not form and replication stops
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The Sanger method requires
Multiple copies of single stranded template DNA A suitable primer (a small piece of DNA that can
pair with the template DNA to act as a starting point for replication)
DNA polymerase (an enzyme that copies DNA, adding new nucleotides to the 3’ end of the template
A ‘pool’ of normal nucleotides A small proportion of dideoxynucleotides
labeled in some way ( radioactively or with fluorescent dyes)
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The template DNA pieces are replicated, incorporating normal nucleotides, but occasionally and at random dideoxy (DD) nucleotides are taken up.
This stops replication on that piece of DNA The result is a mix of DNA lengths, each
ending with a particular labeled DDnucleotide.
Because the different lengths ‘travel’ at different rates during electrophoresis, their order can be determined.
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A Nanodrop readout :DNA purity & concentration is checked by spectrophotometer
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Preparing the wells
The Sample wells are loaded with DNA to be sequenced. Great care needs to be taken to ensure that each sample goes into its assigned well.
Reagents are added (water, dye, primers) in required amounts
The sample wells are ‘spun’ to ensure that the DNA and reagents are mixed and at the bottom of the sample wells.
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The samples are run through a cycle sequencing process to get the fluorescent dyes incorporated by the DNA.The DNA and reagents are alternately heated and cooled over a2 1/2 hour period.
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Mlh1 amplicons
Exon 1; amplicon 1 5’ UTR:
Tggggctggatggcgtaagctacagctgaaggaagaacgtgagcacgaggcactgaggtg
Exon 1: ATTGGCTGAAGGCACTTCCGTTGAGCATCTAGACGTTTCCTTGGCTCTTCTGGCGCCAAAATGTCGTTCGTGGCAGGGGTTATTCGGCGGCTGGACGAGACAGTGGTGAACCGCATCGCGGCGGGGGAAGTTATCCAGCGGCCAGCTAATGCTATCAAAGAGATGATTGAGAACTG
Intron1: gtacggagggagtcgagccgggctcacttaagggctacgacttaacgggccgcgtcactcaatggcgcggacacgcctctttgcccgggcagaggcatgtacagcgcatgcccacaacggcggaggccgccgggttccctgacgtgccagtcaggccttctccttttccgcagaccgtgtgt
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Microsatellites
Microsatellites also known as variable nucleotide tandem repeats (VNTRs), are loci throughout the genome in which a short motif, such as a dinucleotide or mononucleotide sequence, is repeated at least several times.
AAAAAAAAAAAAAAAAAAAAAAAAAAAAA
CACACACACACACACACACACACACACACA
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Microsatellites
Microsatellites refer to long segments of nontranscribed DNA that are composed of a repeating mononucleotide (eg, AAAAAAAAAAAAAAAA) or dinucleotide sequences (eg, GTGTGTGTGTGTGT).
These long DNA sequences provide a simple indicator of genetic mutation rate and risk because mutations are readily apparent in these long repeating sequences.
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MSI
MSI is the hallmark of lynch syndrome occuring in >90% of lynch syndrome.
Aaltonen L.A et.al science 1993;260:812-816Altonen et.al cancer res-1994;54;1645
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MSI
Only 20% to 25% of patients who have MSI-H colon cancer have an MMR gene mutation and Lynch syndrome .Barnetson RA, Tenesa A, et al. . N Engl J Med 2006;356(26):2751–63.
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MSI
The finding of microsatellite instability should lead to genetic testing because it is found in more than 90% of patients who have Lynch syndrome,but in only 15% to 20% of patients who have sporadic colon cancer.
ICG-HNPCC
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Mismatch Repair Genes
MMR are called caretaker genes because of their important role in policing the integrity of the genome and correcting DNA replication errors.
MMR genes that undergo a loss of function contribute to carcinogenesis by accelerating tumor progression.
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Mismatch Repair Genes
Mutations in MMR genes produce microsatellite instability.
Microsatellites are repetitive sequences of DNA that appear to be randomly distributed throughout the genome.
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Mismatch Repair Genes
Stability of microsatellite sequences is a good measure of the general integrity of the genome.
MMR gene mutations result in errors in S phase when DNA is newly synthesized and copied.
Microsatellite instability exists in 10% to 15% of sporadic tumors and in 95% of tumors in patients with HNPCC. Even so, only 50% of patients diagnosed with HNPCC have readily identifiable MMR mutations.
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Mismatch Repair Genes
Stability of these sequences is a good measure of the general integrity of the genome.
MMR gene mutations result in errors in S phase when DNA is newly synthesized and copied.
Microsatellite instability exists in 10% to 15% of sporadic tumors and in 95% of tumors in patients with HNPCC. Even so, only 50% of patients diagnosed with HNPCC have readily identifiable MMR mutations.
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Age Number
</=20 221-30 431-40 941-50 1051-60 861-70 471-80 3total 41
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Observations
Total number of cases till now 41 Male 21 Female 20
<50 yrs 25 >50 yrs 16
Rectal ca 20 Colonic 21
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Site Number Caecum 4Ascending colon 4Hepatic flx. 2Transverse colon +1Splenic flex. 1Descending colon 4+1Sigmoid colon 3Rectum 20Total 41
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Sex distribution
number
male female
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FAMILY HYSTORY
SIGNIFICANT IN 10 PATIENTS 1st degree relatives with cancer 8
patients Second primary in 2 patients
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Patient no 14
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Patient no 14
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Patient no 6,8
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Patient no 2,3,4,5 for 5 exons
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Patient no 2,3,4,5 for 5 exons
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Our plan of work for next 3 months
12 patients suspected HNPCC – priority Complete investigation DNA isolation
Tumor Genomic
MSI IHC DNA amplification of specific gene all exons Sequencing Final result
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Next
All patients who are included in study – MSI IHC
MSI+ IHC + DNA-SEQUENCING FINAL RESULT
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THANK YOU
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