High-resolution genomic profiling of chromosomal aberrations using Infinium whole-genome genotyping

TLDR

Array‑CGH detects chromosomal aberrations, and SNP‑CGH extends this by simultaneously measuring signal intensity and allelic composition to identify copy‑number changes and copy‑neutral loss‑of‑heterozygosity. The study demonstrates that Infinium whole‑genome genotyping BeadChips (109k and 317k SNPs) can detect constitutional and tumor chromosomal aberrations at sub‑100 kb resolution and introduces single‑sample and paired‑sample analysis modes. Detection is achieved by modeling statistical power with an X‑chromosome titration system, assessing sensitivity through mixing tumor and normal gDNA, and visualizing log‑ratio and allelic‑ratio plots in a genome browser, with the single‑sample mode referencing canonical genotype clusters from ~120 controls and the paired mode using the individual’s normal sample. SNP‑CGH identified homozygous and hemizygous deletions, copy‑neutral LOH, duplications, and amplifications, and the two analysis modes differ in performance for low‑input, fragmented, and Phi29‑pre‑amplified DNA.

Abstract

Array-CGH is a powerful tool for the detection of chromosomal aberrations. The introduction of high-density SNP genotyping technology to genomic profiling, termed SNP-CGH, represents a further advance, since simultaneous measurement of both signal intensity variations and changes in allelic composition makes it possible to detect both copy number changes and copy-neutral loss-of-heterozygosity (LOH) events. We demonstrate the utility of SNP-CGH with two Infinium whole-genome genotyping BeadChips, assaying 109,000 and 317,000 SNP loci, to detect chromosomal aberrations in samples bearing constitutional aberrations as well tumor samples at sub-100 kb effective resolution. Detected aberrations include homozygous deletions, hemizygous deletions, copy-neutral LOH, duplications, and amplifications. The statistical ability to detect common aberrations was modeled by analysis of an X chromosome titration model system, and sensitivity was modeled by titration of gDNA from a tumor cell with that of its paired normal cell line. Analysis was facilitated by using a genome browser that plots log ratios of normalized intensities and allelic ratios along the chromosomes. We developed two modes of SNP-CGH analysis, a single sample and a paired sample mode. The single sample mode computes log intensity ratios and allelic ratios by referencing to canonical genotype clusters generated from ∼120 reference samples, whereas the paired sample mode uses a paired normal reference sample from the same individual. Finally, the two analysis modes are compared and contrasted for their utility in analyzing different types of input gDNA: low input amounts, fragmented gDNA, and Phi29 whole-genome pre-amplified DNA.