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Epigenetics. 2018;13(1):19-32. doi: 10.1080/15592294.2017.1411443. Epub 2018 Jan 30.

Agreement in DNA methylation levels from the Illumina 450K array across batches, tissues, and time.

Author information

1
a Lady Davis Institute , Jewish General Hospital , Montreal , QC , Canada.
2
b Ludmer Centre for Neuroinformatics and Mental Health , McGill University , Montreal , QC , Canada.
3
c Douglas Hospital Research Centre , McGill University , Montreal , QC , Canada.
4
d Sackler Program for Epigenetics & Psychobiology , McGill University , Montreal , QC , Canada.
5
e Canadian Institute for Advanced Research , Child and Brain Development Program , Toronto , ON , Canada.
6
f Centre for Molecular Medicine and Therapeutics, Department of Medical Genetics , and BC Children's Hospital Research Institute, University of British Columbia , Vancouver , BC , Canada.
7
g McMaster University , ON , Canada.
8
h Singapore Institute of Clinical Sciences , Singapore.
9
i Departments of Oncology and Human Genetics , McGill University , Montreal , QC , Canada.
10
j Department of Epidemiology, Biostatistics and Occupational Health , McGill University , Montreal , QC , Canada.

Abstract

Epigenome-wide association studies (EWAS) have focused primarily on DNA methylation as a chemically stable and functional epigenetic modification. However, the stability and accuracy of the measurement of methylation in different tissues and extraction types is still being actively studied, and the longitudinal stability of DNA methylation in commonly studied peripheral tissues is of great interest. Here, we used data from two studies, three tissue types, and multiple time points to assess the stability of DNA methylation measured with the Illumina Infinium HumanMethylation450 BeadChip array. Redundancy analysis enabled visual assessment of agreement of replicate samples overall and showed good agreement after removing effects of tissue type, age, and sex. At the probe level, analysis of variance contrasts separating technical and biological replicates clearly showed better agreement between technical replicates versus longitudinal samples, and suggested increased stability for buccal cells versus blood or blood spots. Intraclass correlations (ICCs) demonstrated that inter-individual variability is of similar magnitude to within-sample variability at many probes; however, as inter-individual variability increased, so did ICC. Furthermore, we were able to demonstrate decreasing agreement in methylation levels with time, despite a maximal sampling interval of only 576 days. Finally, at 6 popular candidate genes, there was a large range of stability across probes. Our findings highlight important sources of technical and biological variation in DNA methylation across different tissues over time. These data will help to inform longitudinal sampling strategies of future EWAS.

KEYWORDS:

Intraclass correlations; methylation; redundancy analysis; replication; tissue stability

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