Copy Number Studies in Noisy Samples.
System noise was analyzed in 77 Affymetrix 6.0 samples from a previous clinical study of copy number variation (CNV). Twenty-three samples were classified as eligible for CNV detection, 29 samples as ineligible and 25 were classified as being of intermediate quality. New software ("noise-free-cnv") was developed to visualize the data and reduce system noise. Fresh DNA preparations were more likely to yield eligible samples (p < 0.001). Eligible samples had higher rates of successfully genotyped SNPs (p < 0.001) and lower variance of signal intensities (p < 0.001), yielded fewer CNV findings after Birdview analysis (p < 0.001), and showed a tendency to yield fewer PennCNV calls (p = 0.053). The noise-free-cnv software visualized trend patterns of noise in the signal intensities across the ordered SNPs, including a wave pattern of noise, being co-linear with the banding pattern of metaphase chromosomes, as well as system deviations of individual probe sets (per-SNP noise). Wave noise and per-SNP noise occurred independently and could be separately removed from the samples. We recommend a two-step procedure of CNV validation, including noise reduction and visual inspection of all CNV calls, prior to molecular validation of a selected number of putative CNVs.
Neurology Department, University of Heidelberg, INF 400, Heidelberg D69120, Germany. Philip.Ginsbach@t-online.de.
Philip
P
Ginsbach
Division of Molecular Genetic Epidemiology, German Cancer Research Center, INF 280, Heidelberg D69120, Germany. c.bowang@dkfz-heidelberg.de.
Bowang
B
Chen
Neurology Department, University of Heidelberg, INF 400, Heidelberg D69120, Germany. jiangyanxiang@googlemail.com.
Yanxiang
Y
Jiang
Stroke Unit and Department of Neurology, University Hospital Basel, Petersgraben 4, Basel CH4031, Switzerland. Stefan.Engelter@usb.ch.
Stefan T
ST
Engelter
Neurology Department, University of Heidelberg, INF 400, Heidelberg D69120, Germany. Caspar.Grond-Ginsbach@med.uni-heidelberg.de.
Caspar
C
Grond-Ginsbach
copy number variation (CNV); noise reduction; noise-free-cnv software; per-SNP noise; validation of CNV findings; variance; wave noise