vignettes/age-tutorial.md

In perishky/meffonym: DNA methylation exposure and phenotypic archive

DNA methylation age and acceleration

Dataset

We will analyze data used to derive the Hannum et al. DNA methylation age predictor.

Hannum G, Guinney J, Zhao L, Zhang L et al. Genome-wide methylation profiles reveal quantitative views of human aging rates. Mol Cell 2013 Jan 24;49(2):359-67. PMID: 23177740

Retrieve the data from the Gene Expression Omnibus (GEO) website (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE40279).

source(system.file("read-gse-matrix-file.r", package="meffonym"))

file <-  "GSE40279_series_matrix.txt.gz"
gse <- "GSE40279"
url <- file.path("ftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE40nnn", gse,
                 "matrix", file)

if (!file.exists(file))
    download.file(url, destfile=file) ## 1.2Gb file

if (!exists("hannum"))
    hannum <- read.gse.matrix.file(file) ## ~15 minutes

Extract phenotypes/exposures.

extract.characteristic <- function(ch) {
    sub("[^:]+: (.*)", "\\1", ch)
}
hannum$samples$age <- as.numeric(extract.characteristic(hannum$samples$characteristics_ch1))
hannum$samples$gender <- extract.characteristic(hannum$samples$characteristics_ch1.3)
hannum$samples$ethnicity <- extract.characteristic(hannum$samples$characteristics_ch1.4)

Calculate scores for all available models

library(meffonym)

scores <- cbind(age=hannum$samples$age,
                sapply(meffonym.models(), function(model) {
                    meffonym.score(hannum$dnam, model)$score
                }))

Calculate correlations between scores.

cor(scores)

##                         age  age.hannum age.horvath
## age             1.000000000  0.94607431  0.91834357
## age.hannum      0.946074305  1.00000000  0.94750672
## age.horvath     0.918343573  0.94750672  1.00000000
## ga.bohlin.1se  -0.186930069 -0.17344962 -0.18016336
## ga.bohlin.min  -0.237881118 -0.22397250 -0.23879848
## ga.knight      -0.004742566  0.01194531  0.02103212
##                ga.bohlin.1se ga.bohlin.min    ga.knight
## age               -0.1869301    -0.2378811 -0.004742566
## age.hannum        -0.1734496    -0.2239725  0.011945310
## age.horvath       -0.1801634    -0.2387985  0.021032121
## ga.bohlin.1se      1.0000000     0.9440823  0.434868330
## ga.bohlin.min      0.9440823     1.0000000  0.420777076
## ga.knight          0.4348683     0.4207771  1.000000000

Calculate differences between biological and estimated age.

apply(scores[,-1], 2, function(estimate) quantile(estimate-scores[,"age"]))

##      age.hannum age.horvath ga.bohlin.1se ga.bohlin.min
## 0%   -17.953761  -30.427276      176.8630      164.2975
## 25%    1.315673   -5.777963      215.3069      209.8056
## 50%    4.906997   -2.317217      225.8057      220.6148
## 75%    7.870733    1.037909      238.0843      232.8203
## 100%  27.105114   31.887875      281.9626      284.1008
##       ga.knight
## 0%   -55.013400
## 25%  -29.301776
## 50%  -18.833782
## 75%   -8.492379
## 100%  27.836865

Calculate age acceleration

Age accelaration is obtained by adjusting age estimates for actual age.

age.scores <- scores[,c("age.horvath","age.hannum")]

acc <- apply(age.scores, 2, function(estimate) {
    residuals(lm(estimate ~ scores[,"age"]))
})

Test age acceleration differences between the sexes. Both Hannum and Horvath scores show greater acceleration in males than females.

t(sapply(colnames(acc), function(name) {
    acc <- acc[,name]
    coef(summary(lm(acc ~ gender, data=hannum$samples)))["genderM",]
}))

##             Estimate Std. Error  t value     Pr(>|t|)
## age.horvath 1.546429  0.3908939 3.956134 8.449921e-05
## age.hannum  2.215048  0.3206417 6.908173 1.166350e-11

Obtaining estimates identical to the online Horvath clock

The following estimates are equivalent to that of the Horvath clock. The calculation can be time consuming, so we will obtain estimates for only the first 10.

horvath.est <- meffonym.horvath.age(hannum$dnam[,1:10]) ## 1-2 minutes

These estimates are obtained in two steps: normalizing the methylation data to 'gold standard' used by Horvath when developing the model, and then applying the model in the normalized data.

standard <- meffonym.horvath.standard()
## step 1: normalization (1-2 minutes)
dnam.norm <- meffonym.bmiq.calibration(hannum$dnam[,1:10], standard) 
## step 2: model application
equiv.est <- meffonym.score(dnam.norm, "age.horvath")

They are the same.

cor(equiv.est$score, horvath.est$score)

## [1] 1

equiv.est$score - horvath.est$score

##  [1] 0 0 0 0 0 0 0 0 0 0

Normalization in this case has a fairly minor effect on the age estimates.

cor(age.scores[1:10,"age.horvath"], horvath.est$score)

## [1] 0.9996503

sort(age.scores[1:10, "age.horvath"] - horvath.est$score)

##  [1] -1.5863928 -1.4992797 -1.4157137 -1.3949272 -0.9008319 -0.8854542
##  [7] -0.8767604 -0.7215569 -0.7183931 -0.4808198

Calculate scores for a new model

model <- meffonym.get.model("age.horvath")
idx <- order(abs(model$coefficients), decreasing=T)[1:10]
model$coefficients <- model$coefficients[idx]
meffonym.add.model("age.horvath.10",
                     variables=names(model$coefficients),
                     coefficients=model$coefficients,
                     description="Horvath model with only the top 10 effect sizes.")

Estimate age with that new model.

ten.est <- meffonym.score(hannum$dnam, "age.horvath.10")

The result is obviously similar but 10 CpG sites is obviously not the same as 353.

cor(ten.est$score, scores[,"age.horvath"])

## [1] 0.7324617

Document generated from R Markdown

library(knitr)
library(markdown)

options(markdown.HTML.options=union('toc', getOption("markdown.HTML.options")))

knit("age-tutorial.rmd", "age-tutorial.md")
markdownToHTML("age-tutorial.md","age-tutorial.html", stylesheet="style.css")

perishky/meffonym documentation built on April 5, 2024, 12:21 a.m.