Discrimination between human populations using a small number of differentially methylated CpG sites:  A preliminary study using lymphoblastoid cell lines and peripheral blood samples of Caucasian and Chinese origin.

Abstract

Background Epigenetics is one of the factors shaping natural variability observed among human populations. A small proportion of heritable inter-population differences are observed in the context of both the genome-wide methylation level and the methylation status of individual CpG sites. It has been demonstrated that a limited number of carefully selected differentially methylated sites may allow discrimination between main human populations. However, most of the few published results have been performed exclusively on B-lymphocyte cell lines. Results The goal of our study was to identify a set of CpG sites sufficient to discriminate between Caucasian and Chinese populations based on the difference in the DNA methylation profile not only in cell lines but also in primary cell samples. The preliminary selection of CpG sites differentially methylated in these two populations (pop-diff-met CpGs) was based on the analysis of two groups of commercially available ethnically-specific B-lymphocyte cell lines, performed using Illumina Infinium Human Methylation 450 BeadChip Array. A subset of ten pop-diff-met CpGs characterized by the best differentiating criteria (|Mdiff|>1, q<0.05; lack of the confounding genomic features), and ten additional CpGs in their immediate vicinity, were further tested using pyrosequencing technology in both B-lymphocyte cell lines and in the primary samples of the peripheral blood representing two analyzed populations. To assess the population-discriminating potential of the selected set of CpGs (further referred to as “composite pop(CEU-CHB)-diff-met CpG marker”), three classification methods were applied. The predictive ability of the composite 8-site pop(CEU-CHB)-diff-met CpG marker was assessed using 10-fold cross-validation method on two independent sets of samples. Concussions Our results showed that less than 10 pop-diff-met CpG sites may distinguish Caucasian and Chinese populations; importantly, this small composite pop-diff-met CpG marker performs well in both lymphoblastoid cell lines and in non-homogenous blood samples.