get.diff.meth {ELMER} | R Documentation

## Identify hypo/hyper-methylated CpG sites between two groups (i.e. normal vs tumor samples, treated vs untreated).

### Description

get.diff.meth applys one-way t-test to identify the CpG sites that are significantly hypo/hyper-methyalated using proportional samples (defined by minSubgroupFrac option) from group 1 and group 2. The P values will be adjusted by Benjamini-Hochberg method. Option pvalue and sig.dif will be the criteria (cutoff) for selecting significant differentially methylated CpG sites. If save is TURE, two getMethdiff.XX.csv files will be generated (see detail).

### Usage

    get.diff.meth(data, diff.dir = "hypo", cores = 1, mode = "unsupervised",
      minSubgroupFrac = 0.2, pvalue = 0.01, group.col, min.samples = 5,
      group1, group2, test = t.test, sig.dif = 0.3, dir.out = "./",
      save = TRUE)

### Arguments

`data` | A multiAssayExperiment with DNA methylation and Gene Expression data. See `createMAE` function.
`diff.dir` | A character can be "hypo", "hyper" or "both", showing differential methylation direction. It can be "hypo" which is only selecting hypomethylated probes (one tailed test); "hyper" which is only selecting hypermethylated probes (one tailed test); or "both" which are probes differenly methylated (two tailed test).
`cores` | A interger which defines the number of cores to be used in parallel process. Default is 1: no parallel process.
`mode` | A character. Can be "unsupervised" or "supervised". If "supervised", the minSubgroupFrac argument will be set to 1 to use all samples from both groups to find the differently methylated regions. The supervised mode should be used when all samples from both groups are considered homogenous (i.e. treated vs untreated, molecular subtype A vs molecular subtype B), while unsupervised mode should be used when there is at least one group with heterogenous samples (i.e tumor samples).
`minSubgroupFrac` | A number ranging from 0 to 1, specifying the fraction of extreme samples from group 1 and group 2 that are used to identify the differential DNA methylation. The default is 0.2 because we typically want to be able to detect a specific (possibly unknown) molecular subtype among tumor; these subtypes often make up only a minority of samples, and 20% was chosen as a lower bound for the purposes of statistical power. If you are using pre-defined group labels, such as treated replicates vs. untreated replicated, use a value of 1.0 (Supervised mode)
`pvalue` | A number specifies the significant P value (adjusted P value by BH) threshold Limit for selecting significant hypo/hyper-methylated probes. Default is 0.01 If pvalue is smaller than pvalue than it is considered significant.
`group.col` | A column defining the groups of the sample. You can view the available columns using: colnames(MultiAssayExperiment::colData(data)).
`min.samples` | Minimun number of samples to use in the analysis. Default 5. If you have 10 samples in one group, minSubgroupFrac is 0.2 this will give 2 samples in the lower quintile, but then 5 will be used.
`group1` | A group from group.col. ELMER will run group1 vs group2. That means, if direction is hyper, get probes hypermethylated in group 1 compared to group 2.
`group2` | A group from group.col. ELMER will run group1 vs group2. That means, if direction is hyper, get probes hypermethylated in group 1 compared to group 2.
`test` | Statistical test to be used. Options: t.test (DEFAULT), wilcox.test
`sig.dif` | A number specifies the smallest DNA methylation difference as a cutoff for selecting significant hypo/hyper-methylated probes. Default is 0.3.
`dir.out` | A path specify the directory for outputs. Default is is current directory.
`save` | A logic. When TRUE, two getMethdiff.XX.csv files will be generated (see detail)

### Details

save: When save is TRUE, function will generate two XX.csv files.The first one is named getMethdiff.hypo.probes.csv (or getMethdiff.hyper.probes.csv depends on diff.dir). The first file contains all statistic results for each probe. Based on this file, user can change different P value or sig.dir cutoff to select the significant results without redo the analysis. The second file is named getMethdiff.hypo.probes.significant.csv (or getMethdiff.hyper.probes.significant.csv depends on diff.dir). This file contains statistic results for the probes that pass the significant criteria (P value and sig.dir). When save is FALSE, a data frame R object will be generate which contains the same information with the second file.

### Value

Statistics for all probes and significant hypo or hyper-methylated probes.

### References

Yao, Lijing, et al. "Inferring regulatory element landscapes and transcription factor networks from cancer methylomes." Genome biology 16.1 (2015): 1.

### Examples

    data <- ELMER:::getdata("elmer.data.example")
    Hypo.probe <- get.diff.meth(data,
                                diff.dir="hypo",
                                group.col = "definition",
                                group1 = "Primary solid Tumor",
                                group2 = "Solid Tissue Normal",
                                sig.dif = 0.1) # get hypomethylated probes
    Hyper.probe <- get.diff.meth(data,
                                diff.dir="hyper",
                                group.col = "definition",
                                sig.dif = 0.1) # get hypomethylated probes

[Package ELMER version 2.4.4 Index]