Sample handling process and quality assurance
DNA extraction
deCODE will accept DNA, whole blood, saliva, or buffy coat samples. For clients who do not have DNA readily available deCODE will extract
DNA utilizing our in-house developed semi-automated
platform for high quality, high-throughput DNA extraction. Excess DNA can
be banked at our facility for prospect fine-mapping analysis.
Whole-genome amplification
We amplify DNA from samples with
limited amounts of DNA by whole genome amplification using an optimized high-throughput protocol based on the Phi29 polymerase. We will accept small amounts of genomic DNA, blood or buccal samples. As little as 10 ng for either 10 μg or 40 μg yield and 100 ng for 150 μg of DNA. Quality checks are performed by genotyping a panel of 10 highly informative microsatellite markers accross multiple chromosomes, including the X chromosome. This method has been validated for both microsatellite and SNP genotyping.
Sample tracking
deCODE has created an automated sample processing and tracking software platform
to support high-throughput data generation and monitoring. Samples are
tracked using barcode labels and non-personally identifiable tracking numbers.
Quality control
Prior to initiating a full-scale production effort, all samples for the project
will be tested. For microsatellite genotyping we test 8 markers to identify problem samples. CEPH family
DNA is used as control. For genotyping with Illumina Sentrix® arrays we test a subset of the client samples and one reference sample to identify potential problems. We do not request pedigree information, although
data on family relationships of individuals in a sample set will allow
more accurate quality control.
Microsatellite genotyping
For microsatellite genotyping projects amplified fragments are analyzed by capillary electrophoresis utilizing ABI 3730 DNA analyzers. deCODE has optimized the protocol for
rapid, accurate, and cost-effective analysis. deCODE uses it's proprietary deCODE Allele Caller (DAC) software for automated
allele calling. The analysis consistently gives greater than 99% accuracy
of genotyping calls. PCR reactions are set up in multiplex reactions with fluorescently-labeled
primer pairs selected to amplify highly informative di-, tri-, and tetra-microsatellite
loci. We have performed extensive optimization of each primer pair to improve
performance and reliability. deCODE's facility is equipped with 4 high-throughput
liquid handling robots with a total capacity to handle samples from over
1,000 individuals per day in preparation for genome-wide scans.
SNP fine-mapping
We use an in-house optimized platform based on technology developed by Nanogen, Inc. The platform uses the highly discriminating endonuclease IV and allelic discrimination is accomplished using detection probes specific to each expected genotype. We are able to analyze SNPs which have proven difficult to genotype by other platforms. SNPs are analyzed by end point scatter plot analysis using the ABI® 7900HT Sequence Detection System. deCODE uses it's proprietary deCODE Allele Caller (DAC) software for automated allele calling and Hardy-Weinberg checks and LD tests to ensure high-quality results.
SNP whole-genome scans
We genotype samples using Illumina's Sentrix® BeadChips, powered by the Infinium® II assay. The Sentrix® arrays enable whole-genome genotyping of hundreds of thousands of tagSNP markers derived from the International HapMap project. TagSNPs are loci that can serve as proxies for many other SNPs and greatly improve the power of association studies. DNA samples are isothermally amplified and fragmented by a controlled enzymatic process. Samples are applied to BeadChips where DNA samples anneal to locus specific 50-mers during the hybridization step. Products are subsequently fluorescently stained and the intensities of the beads' fluorescenses is detected by an Illumina BeadArray Reader. We use Illumina's software for automated genotype calling.
Genotyping results
For microsatellites genotyping results will be reported as allele sizes of the polymorphic markers
of called alleles as well as values normalized to a CEPH individual. For SNPs genotyping results are reported as alleles of each marker. The
data report is delivered as a ASCII text file, compatible with existing
genetic linkage and association software packages. The data is delivered via a secure server, which can
be accessed with a personal username and password, in strictest confidence.
