---
title: "MethylMix"
subtitle: "An R package for identifying DNA methylation driven genes"
author: |
    | Olivier Gevaert
    |
    | Stanford Center for Biomedical Informatics
    | Department of Medicine
    | 1265 Welch Road
    | Stanford CA, 94305-5479
date: "`r Sys.Date()`"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{MethylMix}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---


##1. Getting started

__Installing the package.__ To install the _MethylMix_ package, the easiest way is through bioconductor:

```{r, eval=FALSE}
source("http://bioconductor.org/biocLite.R")
biocLite(MethylMix)
```

Other ways to install MethylMix is to first download the appropriate file for 
your platform from the Bioconductor website [http://www.bioconductor.org/](http://www.bioconductor.org/). 
For Windows, start R and select the `Packages` menu, then `Install package from local zip file`.
Find and highlight the location of the zip file and click on `open`. For Linux/Unix, use the usual command 
`R CMD INSTALL` or install from bioconductor.

__Loading the package.__ To load the `MethylMix` package in your R session, type `library(MethylMix)`.

__Help files.__  Detailed information on `MethylMix` package 
functions can be obtained in the help files. For example, to view the help file 
for the function `MethylMix` in a R session, use `?MethylMix`.

##2. Introduction

DNA methylation is a mechanism whereby a methyl-group is added onto a CpG site. 
Methylation of these CpG sites is associated with gene silencing and is an 
important mechanism for normal tissue development and is often involved in 
diseases such as cancer. Recently, many high throughput data has been generated 
profiling CpG site methylation on a genome wide bases. This has created large 
amounts of data on DNA methylation for many disease. Computational analysis of 
DNA methylation data is required to identify potentiall aberrant DNA methylation 
compared to normal tissue. MethylMix (Gevaert 2015; Gevaert, Tibshirani & Plevritis 2015) was developed to tackle this question using 
a computational approach. MethylMix identifies differential and functional DNA 
methylation by using a beta mixture model to identify subpopulations of samples 
with different DNA methylation compared to normal tissue. Functional DNA 
methylation refers to a significant negative correlation based on matched gene 
expression data. Together MethylMix outputs hyper and hypomethylated genes which 
can be used for downstream analysis, and are called MethylMix drivers. MethylMix 
was designed for cis-regulated promoter differential methylation and works best 
when specific CpG sites are profiled associated with a gene. For example using 
data from the 27k and 450k Infinium platforms. 

##3. Data access and preprocessing

The `MethylMix` package provides functions to access and preprocess data at The Cancer Genome Atlas (TCGA) 
portal. Given a cancer type indicated by TCGA's code and a path to save downloaded files, all the download and
preprocess of data can be executed with:

```{r, eval=FALSE}
cancerSite <- "OV"
targetDirectory <- paste0(getwd(), "/")
GetData(cancerSite, targetDirectory)
```

All functions in the `MethylMix` package can be run in parallel, if the user provides a parallel set up, like
the following:

```{r, eval=FALSE}
cancerSite <- "OV"
targetDirectory <- paste0(getwd(), "/")

library(doParallel)
cl <- makeCluster(5)
registerDoParallel(cl)
GetData(cancerSite, targetDirectory)
stopCluster(cl)
```

The `GetData` function downloads DNA methylation data and gene expression. The methylation data
is provided using 27k or 450k Illumina platforms. If both 27k and 450k files are found, the data
is carefully combined. For gene expression, either microarray (Agilent), RNA sequencing data or
both are available. The `MethylMix` package downloads RNA sequencing data for all cancer sites
except for ovarian and gliobastoma cancer sites (few RNA-seq samples available). 
For the preprocessing of the data, we package perform missing value estimation and batch
correction (using Combat).
Finally, as in the TCGA case, when only probe level Illumina data is available, mapping probes to genes is 
recommended before building mixture models. This allows to focus on cis-
regulated differential methylation by only focusing on differential methylation 
of CpG sites to their closest gene transcripts. Both the 27k and 450k Illumina 
platforms have database R packages that provide the necessary mapping 
information. We use the annotation to map probes to genes, before clustering the probes
within each gene. This whole process can take a long time, depending of the size of the data.

It is also possible to perform each one of these task individually using other functions 
in the `MethylMix` package, as in the following example:

```{r, eval=FALSE, tidy=TRUE}
cancerSite <- "OV"
targetDirectory <- paste0(getwd(), "/")

cl <- makeCluster(5)
registerDoParallel(cl)

# Downloading methylation data
METdirectories <- Download_DNAmethylation(cancerSite, targetDirectory)
# Processing methylation data
METProcessedData <- Preprocess_DNAmethylation(cancerSite, METdirectories)
# Saving methylation processed data
saveRDS(METProcessedData, file = paste0(targetDirectory, "MET_", cancerSite, "_Processed.rds"))

# Downloading gene expression data
GEdirectories <- Download_GeneExpression(cancerSite, targetDirectory)
# Processing gene expression data
GEProcessedData <- Preprocess_GeneExpression(cancerSite, GEdirectories)
# Saving gene expression processed data
saveRDS(GEProcessedData, file = paste0(targetDirectory, "GE_", cancerSite, "_Processed.rds"))

# Clustering probes to genes methylation data
METProcessedData <- readRDS(paste0(targetDirectory, "MET_", cancerSite, "_Processed.rds"))
res <- ClusterProbes(METProcessedData[[1]], METProcessedData[[2]])

# Putting everything together in one file
toSave <- list(METcancer = res[[1]], METnormal = res[[2]], GEcancer = GEProcessedData[[1]], GEnormal = GEProcessedData[[2]], ProbeMapping = res$ProbeMapping)
saveRDS(toSave, file = paste0(targetDirectory, "data_", cancerSite, ".rds"))

stopCluster(cl)
```

## 4. Data input for MethylMix

To run MethylMix three data sets of a particular disease are required. The first one is 
the methylation data for the disease samples, `METcancer`, which allows to 
identify methylation states associated with a disease for each gene of interest. 
The second is an appropriate normal or baseline methylation data, `METnormal`, which
is used to distinguish between hyper or increased methylation vs. hypo or decreased methylation.
Finally, the third data set is matched gene expression data for the disease samples, `GEcancer`,
which is used to identify functional differnential methylation by focusing only on differentialy 
methylation that has a significant inversely correlated effect on gene 
expression. 

Each of these three data sets are matrix objects with genes in the 
rows with unique rownames (e.g. gene symbols) and samples or patients in the 
columns with unique patient names. The `GetData` function described before
saves an R object which contains these matrices in the correct format.

As example, small data sets from TCGA of gliobastoma samples are availabe in the
`MethylMix` package:

```{r, tidy=TRUE}
library(MethylMix)
library(doParallel)
data(METcancer)
data(METnormal)
data(GEcancer)
head(METcancer[, 1:4])
head(METnormal)
head(GEcancer[, 1:4])
```

## 5. Running MethylMix

Using the example gliobastoma data provided in the package, `MethylMix` can be 
to identify hypo and hypermethylated genes run as follows:

```{r, tidy=TRUE, warning=F}
MethylMixResults <- MethylMix(METcancer, GEcancer, METnormal)
```

Or in parallel:

```{r, tidy=TRUE, eval=FALSE}
library(doParallel)
cl <- makeCluster(5)
registerDoParallel(cl)
MethylMixResults <- MethylMix(METcancer, GEcancer, METnormal)
stopCluster(cl)
```

The output from the `MethylMix` function is a list with the following elements:

* `MethylationDrivers`: Genes identified as transcriptionally predictive and differentially methylated by MethylMix.
* `NrComponents`: The number of methylation states found for each driver gene.
* `MixtureStates`: A list with the DM-values for each driver gene.
* `MethylationStates`: Matrix with DM-values for all driver genes (rows) and all samples (columns).
* `Classifications`: Matrix with integers indicating to which mixture component each cancer sample was assigned to, for each gene.
* `Models`: Beta mixture model parameters for each driver gene.

Differential Methylation values (DM-values) are defined as the difference between 
the methylation mean in one mixture component of cancer samples and the methylation mean
in the normal samples, for a given gene.

```{r, tidy=TRUE}
MethylMixResults$MethylationDrivers
MethylMixResults$NrComponents
MethylMixResults$MixtureStates
MethylMixResults$MethylationStates[, 1:5]
MethylMixResults$Classifications[, 1:5]
# MethylMixResults$Models
```

## 6. Graphical output

The `MethylMix` package also provides functions to visually represent the findings:

```{r, tidy=TRUE, eval=F}
# Plot the most famous methylated gene for glioblastoma
plots <- MethylMix_PlotModel("MGMT", MethylMixResults, METcancer)
plots$MixtureModelPlot
```

<img src="plot1.png" width="500">

```{r, tidy=TRUE, eval=F}
# Plot MGMT also with its normal methylation variation
plots <- MethylMix_PlotModel("MGMT", MethylMixResults, METcancer, METnormal = METnormal)
plots$MixtureModelPlot
```

<img src="plot2.png" width="500">

```{r, tidy=TRUE, eval=F}
# Plot a MethylMix model for another gene
plots <- MethylMix_PlotModel("ZNF217", MethylMixResults, METcancer, METnormal = METnormal)
plots$MixtureModelPlot
```

<img src="plot3.png" width="500">

```{r, tidy=TRUE, eval=F}
# Also plot the inverse correlation with gene expression (creates two separate plots)
plots <- MethylMix_PlotModel("MGMT", MethylMixResults, METcancer, GEcancer, METnormal)
plots$MixtureModelPlot
plots$CorrelationPlot
```

<img src="plot2.png" width="300"> <img src="plot4.png" width="300">

```{r, eval = FALSE, tidy=TRUE}
# Plot all functional and differential genes
for (gene in MethylMixResults$MethylationDrivers) {
    MethylMix_PlotModel(gene, MethylMixResults, METcancer, METnormal = METnormal)
}
```

## 7. References
Gevaert 0. MethylMix: an R package for identifying DNA methylation-driven genes. Bioinformatics (Oxford, England). 2015;31(11):1839-41. doi:10.1093/bioinformatics/btv020 \n

Gevaert O, Tibshirani R, Plevritis SK. Pancancer analysis of DNA methylation-driven genes using MethylMix. Genome Biology. 2015;16(1):17. doi:10.1186/s13059-014-0579-8 ",


## 8. Sesssion Info

```{r, tidy=TRUE, echo = FALSE}
sessionInfo()
```
