A practical guide to Human Genetics with Lifetime Data

knitr::opts_chunk$set(
  collapse = TRUE,
  #dev="png",
  comment = "#>"
)
library(mets)
 cols <- c("darkred","darkblue","black")
 ltys <- c(1,3,2)
 fig_w <- 5
 fig_h <- 5
 savefig <- TRUE

This vignette demonstrates how to analyze familial resemblance for twins using the \texttt{mets} {\bf R}-package and is accompanying the review by Scheike and Holst (2020).

We consider a data-set in that resembles the data of \cite{Hjelmborg2014} that were based on the NorTwinCan a collaborative research project studying the genetic and environmental components of prostate cancer. The data comprises around 18,000 DZ twins and 11,000 MZ twins. It was a population based register study based on the Danish, Finnish, Norwegian, and Swedish twin registries.

We first illustrate a hazards based analysis to show how one would study dependence in survival data. This needs to be done under assumptions about independent competing risks when the outcome of interest is observed subject to competing risks (here death).

This seems reasonable here since the occurrence of cancer prior to death only contains weak association with the risk of death for the other twin, and vice-versa.

First looking at the data

 library(mets)
 data(prt)

 dtable(prt,~status+cancer)
 dtable(prt,~zyg+country,level=1)

we see that there are 21283 censorings and 6997 deaths (prior to cancer) and a total of 942 prostate cancers. Approximately half the data consist of DZ twins. In addition we see that there are around 10000 twins from Denmark and Sweden, and only 4000 from Norway and Finland, respectively.

Survival


Under assumption of random effects acting independently on different cause specific hazards we can analyse competing risks data considering the cause-specific hazard. Typically, this can be questionable and the cumulative incidence modelling below does not rely on this assumption.

We consider the cause specific hazard of cancer in the competing risks model with death and cancer.

First estimating the marginal hazards for each country.

 # Marginal Cox model here stratified on country without covariates 
 margph <- phreg(Surv(time,cancer)~strata(country)+cluster(id),data=prt)
 plot(margph)

We see that the marginal of Denmark in particular is quite different.

Then we fit a two-stage random effects models with country specific marginals and random-effects variances that differ for MZ and DZ twins.

 # Clayton-Oakes, MLE , overall variance
 fitco1<-twostageMLE(margph,data=prt,theta=2.7)
 summary(fitco1)

 fitco2 <- survival.twostage(margph,data=prt,theta=2.7,clusters=prt$id,var.link=0)
 summary(fitco2)

 ## now with different random effects for MZ and DZ
 mm <- model.matrix(~-1+factor(zyg),prt)
 fitco3<-twostageMLE(margph,data=prt,theta=1,theta.des=mm)
 summary(fitco3)

 fitco4 <- survival.twostage(margph,data=prt,theta=1,clusters=prt$id,var.link=0,theta.des=mm)
 summary(fitco4)
 round(estimate(coef=fitco4$coef,vcov=fitco4$var.theta)$coefmat[,c(1,3:4)],2)

 ## mz kendalls tau
 kendall.ClaytonOakes.twin.ace(fitco4$theta[2],0,K=10000)$mz.kendall
 ## dz kendalls tau
 kendall.ClaytonOakes.twin.ace(fitco4$theta[1],0,K=10000)$mz.kendall

The dependence of MZ twins is much stronger, and is summarized by a variance at $r round(fitco4$coef[2],2)$ in contrast to the $DZ$ variance at $r round(fitco4$coef[1],2)$.

Now we look at the polygenic modelling for survival data, here applied to the cause specific hazards.

 ### setting up design for random effects and parameters of random effects
 desace <- twin.polygen.design(prt,type="ace")

 ### ace model 
 fitace <- survival.twostage(margph,data=prt,theta=1,
       clusters=prt$id,var.link=0,model="clayton.oakes",
       numDeriv=1,random.design=desace$des.rv,theta.des=desace$pardes)
 summary(fitace)

 ### ace model with positive random effects variances
 # fitacee <- survival.twostage(margph,data=prt,theta=1,
 #      clusters=prt$id,var.link=1,model="clayton.oakes",
 #      numDeriv=1,random.design=desace$des.rv,theta.des=desace$pardes)
 #summary(fitacee)

 ### ae model 
 #desae <- twin.polygen.design(prt,type="ae")
 #fitae <- survival.twostage(margph,data=prt,theta=1,
 #      clusters=prt$id,var.link=0,model="clayton.oakes",
 #      numDeriv=1,random.design=desae$des.rv,theta.des=desae$pardes)
 #summary(fitae)

 ### de model 
 desde <- twin.polygen.design(prt,type="de")
 fitde <- survival.twostage(margph,data=prt,theta=1,
       clusters=prt$id,var.link=0,model="clayton.oakes",
       numDeriv=1,random.design=desde$des.rv,theta.des=desde$pardes)
 summary(fitde)

The DE model fits quite well. In summary all shared variance is due to genes and there is no suggestion of a shared environmental effect.

Concordance and Casewise

First we estimate the concordance of joint prostate cancer. The two-twins are censored at the same time, otherwise we would enforce this in the data by artificially censor both twins at the first censoring time. Given, however, that we have the same-censoring assumption satisfied we can do the stanadar Aalen-Johansen product-limit estimator of the concordance probabilities for MZ and DZ twins.

For simplicity we do not do this for each country even though as we show there are big differences between the countries.

 prt <-  force.same.cens(prt,cause="status")

 dtable(prt,~status+cancer)
 dtable(prt,~status+country)
 dtable(prt,~zyg+country)

 ## cumulative incidence with cluster standard errors.
 cif1 <- cif(Event(time,status)~strata(country)+cluster(id),prt,cause=2)
 plot(cif1,se=1)

 cifa <- cif(Event(time,status)~+1,prt,cause=2)

 ### concordance estimator, ignoring country differences. 
 p11 <- bicomprisk(Event(time,status)~strata(zyg)+id(id),data=prt,cause=c(2,2))

 p11mz <- p11$model$"MZ"
 p11dz <- p11$model$"DZ"
 par(mfrow=c(1,2))
 ## Concordance
 plot(p11mz,ylim=c(0,0.1));
 plot(p11dz,ylim=c(0,0.1));

Now we compare the concordance to the marginals to get a measure that takes the marginals into account when evaluating the strength of the association.

 library(prodlim)
 outm <- prodlim(Hist(time,status)~+1,data=prt)

 cifzyg <- cif(Event(time,status)~+strata(zyg)+cluster(id),data=prt,cause=2)
 cifprt <- cif(Event(time,status)~country+cluster(id),data=prt,cause=2)

 times <- 70:100
 cifmz <- predict(outm,cause=2,time=times,newdata=data.frame(zyg="MZ")) ## cause is 2 (second cause) 
 cifdz <- predict(outm,cause=2,time=times,newdata=data.frame(zyg="DZ"))

 ### concordance for MZ and DZ twins<
 cc <- bicomprisk(Event(time,status)~strata(zyg)+id(id),data=prt,cause=c(2,2),prodlim=TRUE)
 ccdz <- cc$model$"DZ"
 ccmz <- cc$model$"MZ"

 cdz <- casewise(ccdz,outm,cause.marg=2) 
 cmz <- casewise(ccmz,outm,cause.marg=2)

 dd <- bicompriskData(Event(time,status)~country+strata(zyg)+id(id),data=prt,cause=c(2,2))
 conczyg <- cif(Event(time,status)~strata(zyg)+cluster(id),data=dd,cause=1)

 par(mfrow=c(1,2))
 plot(conczyg,se=TRUE,col=cols[2:1], lty=ltys[2:1], legend=FALSE,xlab="Age",ylab="Concordance")
 legend("topleft",c("concordance-MZ","concordance-DZ"),col=cols[1:2],lty=ltys[1:2])

 plot(cmz,ci=NULL,ylim=c(0,.8),xlim=c(70,97),legend=FALSE,col=cols[c(1,3,3)],lty=ltys[c(1,3,3)],
      ylab="Casewise",xlab="Age")
  plot(cdz,ci=NULL,ylim=c(0,.8),xlim=c(70,97),legend=FALSE,ylab="Casewise",xlab="Age",
      col=c(cols[2],NA,NA), lty=ltys[c(2,3,3)], add=TRUE)
 with(data.frame(cmz$casewise),plotConfRegionSE(time,casewise.conc,se.casewise,col=cols[1]))
 with(data.frame(cdz$casewise),plotConfRegionSE(time,casewise.conc,se.casewise,col=cols[2]))
 legend("topleft",c("casewise-MZ","casewise-DZ","marginal"),col=cols, lty=ltys, bg="white")

 summary(cdz)
 summary(cmz)

 Cpred(cmz$casewise,80)
 Cpred(cdz$casewise,80)
 dd <- bicompriskData(Event(time,status)~country+strata(zyg)+id(id),data=prt,cause=c(2,2))
 conczyg <- cif(Event(time,status)~strata(zyg)+cluster(id),data=dd,cause=1)

 par(mfrow=c(1,2))
 plot(conczyg,se=TRUE,legend=FALSE,xlab="Age",ylab="Concordance")
 legend("topleft",c("concordance-DZ","concordance-MZ"),col=c(1,2),lty=1)
 plot(cmz,ci=NULL,ylim=c(0,0.6),xlim=c(70,100),legend=FALSE,col=c(2,3,3),ylab="Casewise",xlab="Age",lty=c(1,3))
 plot(cdz,ci=NULL,ylim=c(0,0.6),xlim=c(70,100),legend=FALSE,ylab="Casewise",xlab="Age",
      col=c(1,3,3), add=TRUE, lty=c(2,3))
 legend("topleft",c("casewise-MZ","casewise-DZ","marginal"),col=c(2,1,3),lty=1)
 with(data.frame(cmz$casewise),plotConfRegionSE(time,casewise.conc,se.casewise,col=2))
 with(data.frame(cdz$casewise),plotConfRegionSE(time,casewise.conc,se.casewise,col=1))

The standard errors above are slightly off since they only reflect the uncertainty from the concordance estimation. This can be improved by doing specific calculations for a specific time-point uisng the binomial regression function that gives and iid decomposition for the paramters. We thus apply the binomial regression to estimate the concordance as well as the marginal, and combine the iid decompositions when estimating the standard error. We also do this ignoring country differences.

 ### new version of Casewise for specific time-point based on binreg 
 dd <- bicompriskData(Event(time,status)~country+strata(zyg)+id(id),data=prt,cause=c(2,2))
 newdata <- data.frame(zyg=c("DZ","MZ"),id=1)

 ## concordance 
 bcif1 <- binreg(Event(time,status)~-1+factor(zyg)+cluster(id),dd,time=80,cause=1,cens.model=~strata(zyg))
 pconc <- predict(bcif1,newdata)

 ## marginal estimates
 mbcif1 <- binreg(Event(time,status)~cluster(id),prt,time=80,cause=2)
 mc <- predict(mbcif1,newdata)

 ### casewise with improved se's from log-scale 
 cse <- binregCasewise(bcif1,mbcif1)
 cse

It can be useful also to simply model the concordance given covariates, and in this case we might find it important to adjust for country, or to see if the differences between MZ and DZ are comparable across contries even though clearly DK has a much lower cumulative incidence of prostate cancer.

 ### semi-parametric modelling of concordance 
 dd <- bicompriskData(Event(time,status)~country+strata(zyg)+id(id),data=prt,cause=c(2,2))
 regconc <- cifreg(Event(time,status)~country*zyg,data=dd,prop=NULL)
 regconc
 ### interaction test
 wald.test(regconc,coef.null=5:7)

 regconc <- cifreg(Event(time,status)~country+zyg,data=dd,prop=NULL)
 regconc

 ## logistic link 
 logitregconc <- cifreg(Event(time,status)~country+zyg,data=dd)
 summary(logitregconc)

### library(Publish)
### publish(round(summary(logitregconc)$exp.coef[,-c(2,5)],2),latex=TRUE,digits=2)

Competing risk using additive Gamma

Here we do the cumulative incidence random effects modelling

  times <- seq(50,90,length.out=5)
  cif1 <- comp.risk(Event(time,status)~-1+factor(country)+cluster(id),prt,
           cause=2,times=times,max.clust=NULL)

  mm <- model.matrix(~-1+factor(zyg),prt)
  out1<-random.cif(cif1,data=prt,cause1=2,cause2=2,theta=1,
          theta.des=mm,same.cens=TRUE,step=0.5)
  summary(out1)
  round(estimate(coef=out1$theta,vcov=out1$var.theta)$coefmat[,c(1,3:4)],2)

  desace <- twin.polygen.design(prt,type="ace")

  outacem <- Grandom.cif(cif1,data=prt,cause1=2,cause2=2,
     same.cens=TRUE,theta=c(0.45,0.15),var.link=0,
         step=0.5,theta.des=desace$pardes,random.design=desace$des.rv)
  outacem$score
  summary(outacem)

 ###  variances
 estimate(coef=outacem$theta,vcov=outacem$var.theta,f=function(p) p/sum(p)^2)

 ## AE polygenic model
 # desae <- twin.polygen.design(prt,type="ae")
 # outaem <- Grandom.cif(cif1,data=prt,cause1=2,cause2=2,
 #    same.cens=TRUE,theta=c(0.45,0.15),var.link=0,
 #        step=0.5,theta.des=desae$pardes,random.design=desae$des.rv)
 # outaem$score
 # summary(outaem)
 # estimate(coef=outaem$theta,vcov=outaem$var.theta,f=function(p)     p/sum(p)^2)

 ## AE polygenic model
 # desde <- twin.polygen.design(prt,type="de")
 # outaem <- Grandom.cif(cif1,data=prt,cause1=2,cause2=2,
 #   same.cens=TRUE,theta=c(0.35),var.link=0,
 #   step=0.5,theta.des=desde$pardes,random.design=desde$des.rv)
 # outaem$score
 # summary(outaem)
 # estimate(coef=outaem$theta,vcov=outaem$var.theta,f=function(p) p/sum(p)^2)

  times <- 90
  cif1 <- comp.risk(Event(time,status)~-1+factor(country)+cluster(id),prt,
           cause=2,times=times,max.clust=NULL)

  mm <- model.matrix(~-1+factor(zyg),prt)
  out1<-random.cif(cif1,data=prt,cause1=2,cause2=2,theta=1,
          theta.des=mm,same.cens=TRUE,step=0.5)
  summary(out1)
  round(estimate(coef=out1$theta,vcov=out1$var.theta)$coefmat[,c(1,3:4)],2)

 desde <- twin.polygen.design(prt,type="de")
 outaem <- Grandom.cif(cif1,data=prt,cause1=2,cause2=2,
    same.cens=TRUE,theta=c(0.35),var.link=0,
        step=0.5,theta.des=desde$pardes,random.design=desde$des.rv)
 outaem$score
 summary(outaem)
 estimate(coef=outaem$theta,vcov=outaem$var.theta,f=function(p) p/sum(p)^2)

Competing risk modeling using the Liabilty Threshold model

First we fit the bivariate probit model (same marginals in MZ and DZ twins but different correlation parameter). Here we evaluate the risk of getting cancer before the last double cancer event (95 years)

rm(prt)
data(prt)
prt0 <-  force.same.cens(prt, cause="status", cens.code=0, time="time", id="id")
prt0$country <- relevel(prt0$country, ref="Sweden")
prt_wide <- fast.reshape(prt0, id="id", num="num", varying=c("time","status","cancer"))
prt_time <- subset(prt_wide,  cancer1 & cancer2, select=c(time1, time2, zyg))
tau <- 95
tt <- seq(70, tau, length.out=5) ## Time points to evaluate model in

b0 <- bptwin.time(cancer ~ 1, data=prt0, id="id", zyg="zyg", DZ="DZ", type="cor",
              cens.formula=Surv(time,status==0)~zyg, breaks=tau)
summary(b0)

Liability threshold model with ACE random effects structure

b1 <- bptwin.time(cancer ~ 1, data=prt0, id="id", zyg="zyg", DZ="DZ", type="ace",
              cens.formula=Surv(time,status==0)~zyg, breaks=tau)
summary(b1)

In this case the ACE model fits the data well - it is in fact indistinguishable from the flexible bivariate Probit model as seen by the IPCW weighted AIC measure

AIC(b0, b1)

ACE model with marginal adjusted for country

b2 <- bptwin.time(cancer ~ country, data=prt0, id="id", zyg="zyg", DZ="DZ", type="ace",
              cens.formula=Surv(time,status==0)~zyg+country, breaks=95)
summary(b2)
bt0 <- bptwin.time(cancer ~ 1, data=prt0, id="id", zyg="zyg", DZ="DZ", type="ace", 
              cens.formula=Surv(time,status==0)~zyg,
              summary.function=function(x) x, breaks=tt)
h2 <- Reduce(rbind, lapply(bt0$coef, function(x) x$heritability))[,c(1,3,4),drop=FALSE]
concMZ <- Reduce(rbind, lapply(bt0$coef, function(x) x$probMZ["Concordance",,drop=TRUE]))

par(mfrow=c(1,2))
plot(tt, h2[,1], type="s", lty=1, col=cols[3], xlab="Age", ylab="Heritability", ylim=c(0,1))
confband(tt, h2[,2], h2[,3],polygon=TRUE, step=TRUE, col=Col(cols[3], 0.1), border=NA)
plot(tt, concMZ[,1], type="s", lty=1, col=cols[1], xlab="Age", ylab="Concordance", ylim=c(0,.1))
confband(tt, concMZ[,2], concMZ[,3],polygon=TRUE, step=TRUE, col=Col(cols[1], 0.1), border=NA)

Bivariate probit model at time different time points

system.time(a.mz <- biprobit.time(cancer~1, id="id", data=subset(prt0, zyg=="MZ"),
                               cens.formula = Surv(time,status==0)~1, pairs.only=TRUE,
                                breaks=tt))
system.time(a.dz <- biprobit.time(cancer~1, id="id", data=subset(prt0, zyg=="DZ"),
                               cens.formula = Event(time,status==0)~1, pairs.only=TRUE,
                               breaks=tt))

#system.time(a.zyg <- biprobit.time(cancer~1, rho=~1+zyg, id="id", data=prt, 
#                               cens.formula = Event(time,status==0)~1,
#                               eqmarg=FALSE, fix.cens.weight
#                               breaks=seq(75,100,by=10)))

a.mz
a.dz

plot(conczyg,se=TRUE,legend=FALSE,xlab="Age",ylab="Concordance", ylim=c(0,0.07))
plot(a.mz, ylim=c(0,.07), col=cols[1], lty=ltys[1], legend=FALSE, add=TRUE)
plot(a.dz, col=cols[2], lty=ltys[2], add=TRUE)

Bivariate probit model adjusting for country

system.time(a.mz_country <- biprobit.time(cancer~country, id="id", data=subset(prt0, zyg=="MZ"),
                               cens.formula = Surv(time,status==0)~country, pairs.only=TRUE,
                                breaks=tt))
system.time(a.dz_country <- biprobit.time(cancer~country, id="id", data=subset(prt0, zyg=="DZ"),
                               cens.formula = Event(time,status==0)~country, pairs.only=TRUE,
                               breaks=tt))

a.mz_country
a.dz_country
## ACE model (time-varying) with and without adjustment for country
a1 <- bptwin.time(cancer~1, id="id", data=prt0, type="ace",
                              zyg="zyg", DZ="DZ", 
                              cens.formula=Surv(time,status==0)~zyg,
                              breaks=tt)

#a2 <- bptwin.time(cancer~country, id="id", data=prt0, #type="ace",
#                              zyg="zyg", DZ="DZ", 
#                              #cens.formula=Surv(time,status==0)~country+zyg,
#                              breaks=tt)
plot(a.mz, which=c(6), xlab="Age", ylab="Correlation", ylim=c(0,1), col=cols[1], lty=ltys[1], legend=NULL, alpha=.1)
plot(a.dz, which=c(6), col=cols[2], lty=ltys[2], legend=NULL, add=TRUE, alpha=.1)
legend("topleft", c("MZ tetrachoric correlation", "DZ tetrachoric correlation"),
       col=cols, lty=ltys, lwd=2)

plot(a.mz, which=c(4), xlab="Age", ylab="Relative Recurrence Risk",
     ylim=c(1,20), col=cols[1], lty=ltys[1], legend=NULL, lwd=2, alpha=.1)
plot(a.dz, which=c(4), col=cols[2], lty=ltys[2], legend=NULL, add=TRUE, lwd=2, alpha=.1)
legend("topright", c("MZ relative recurrence risk", "DZ relative recurrence risk"),
       col=cols, lty=ltys, lwd=2)

plot(a1, which=c(5,6), xlab="Age", ylab="Correlation", ylim=c(0,1), col=cols[1:2], lty=ltys[1:2], lwd=2, alpha=0.1,
     legend=c("MZ tetrachoric correlation", "DZ tetrachoric correlation"))

plot(a1, which=c(1), xlab="Age", ylim=c(0,1), col="black", lty=1, ylab="Heritability", legend=NULL, alpha=.1)

SessionInfo

sessionInfo()


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mets documentation built on Sept. 6, 2021, 9:08 a.m.