Positional effects revealed in Illumina methylation array and the impact on analysis

Epigenomics. 2018 May;10(5):643-659. doi: 10.2217/epi-2017-0105. Epub 2018 Feb 22.

Abstract

Aim: We aimed to prove the existence of positional effects in the Illumina methylation beadchip data and to find an optimal correction method.

Materials & methods: Three HumanMethylation450, three HumanMethylation27 datasets and two EPIC datasets were analyzed. ComBat, linear regression, functional normalization and single-sample Noob were used for minimizing positional effects. The corrected results were evaluated by four methods.

Results: We detected 52,988 CpG loci significantly associated with sample positions, 112 remained after ComBat correction in the primary dataset. The pre- and postcorrection comparisons indicate the positional effects could alter the measured methylation values and downstream analysis results.

Conclusion: Positional effects exist in the Illumina methylation array and may bias the analyses. Using ComBat to correct positional effects is recommended.

Keywords: ComBat; DNA methylation; Illumina Infinium MethylationEPIC BeadChip; Infinium Methylation 27K; Infinium Methylation 450K; epigenetics; epigenomics; positional effects.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bias
  • CpG Islands / genetics*
  • DNA Methylation*
  • Genome, Human*
  • Humans
  • Oligonucleotide Array Sequence Analysis / methods*