Pedigree Analysis and Familial Aggregation
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## pedigreePackage: FamAgg
Authors: J. Rainer, D. Taliun, C.X. Weichenberger
Modified: 2024-10-30 07:15:48.688668
Compiled: Wed Oct 30 07:17:10 2024
Introduction
This package provides basic pedigree analysis and plotting utilities as well as a variety of methods to evaluate familial clustering of cases from a given trait. Identification of families or groups of individuals within families with significant aggregation of cases can aid also in the selection of interesting and promising individuals for whole genome or exome sequencing projects.
For kinship coefficient calculations and pedigree plotting the
package relies and extends the functionality of the
kinship2 package [1].
If you use this package please cite Rainer et al. [2].
Basic pedigree operations
In the examples below we perform some simple pedigree operations,
such as plotting the pedigree for an individual or family, finding the
closest common ancestor for a set of individuals in a pedigree or
retrieving the identifiers (IDs) of all ancestors for an individual.
Basic pedigree information is stored in FAData objects,
thus we first generate such an object from a subset of the Minnesota
Breast Cancer Study provided by the kinship2 package. In
the example below, we generate the FAData providing a
data.frame with the pedigree data, alternatively, the
pedigree information could be imported from a file (see Section 3). Upon data set creation the kinship matrix
(i.e. a matrix containing the kinship coefficient between each pair of
individuals in the whole pedigree) is internally calculated using the
functionality from the kinship2 package [1].
library(FamAgg)
data(minnbreast)
## Subsetting to only few families of the whole data set.
mbsub <- minnbreast[minnbreast$famid %in% 4:14, ]
mbped <- mbsub[, c("famid", "id", "fatherid", "motherid", "sex")]
## Renaming column names.
colnames(mbped) <- c("family", "id", "father", "mother", "sex")
## Defining the optional argument age.
endage <- mbsub$endage
names(endage) <- mbsub$id
## Create the object.
fad <- FAData(pedigree = mbped, age = endage)We can access all the pedigree information stored in this object
using the pedigree method, but also using $.
The row names of the pedigree data.frame as well as the
names of the vectors returned by $ are the IDs of the
individuals in the pedigree.
## family id father mother sex
## 1 4 1 NA NA M
## 2 4 2 NA NA F
## 3 4 3 25 4 F
## 4 4 4 1 2 F
## 5 4 5 1 2 M
## 6 4 6 1 2 M## or access individual columns using $.
## The ID of the father (0 representing "founders"):
head(fad$father)## 1 2 3 4 5 6
## NA NA 25 1 1 1## 1 2 3 4 5 6
## NA NA 4 2 2 2## 1 2 3 4 5 6
## M F F F M M
## Levels: M F## 1 2 3 4 5 6
## NA 78.05886 55.50000 48.00000 75.00342 53.63997To extract the pedigree for a single family we can use the
family method, specifying either the ID of the family or
the ID of an individual in the family.
## [1] 43## family id father mother sex
## 1 4 1 NA NA M
## 2 4 2 NA NA F
## 3 4 3 25 4 F
## 4 4 4 1 2 F
## 5 4 5 1 2 M
## 6 4 6 1 2 M## ...which is the same as extracting the family pedigree
## for an individual of this family.
head(family(fad, id = 3))## family id father mother sex
## 1 4 1 NA NA M
## 2 4 2 NA NA F
## 3 4 3 25 4 F
## 4 4 4 1 2 F
## 5 4 5 1 2 M
## 6 4 6 1 2 M## Note that IDs are internally always converted to character,
## thus, using id=3 and id="3" return the same information.
head(family(fad, id = "3"))## family id father mother sex
## 1 4 1 NA NA M
## 2 4 2 NA NA F
## 3 4 3 25 4 F
## 4 4 4 1 2 F
## 5 4 5 1 2 M
## 6 4 6 1 2 MAlternatively, we could subset the FAData to individuals
of a single family.
##
## 4
## 43To explore this family we can plot its pedigree. By default, the
plotting capabilities of the kinship2 package are used to
plot pedigrees, but alternatively, if all required dependencies are
available, the HaploPainter [3] perl script (http://haplopainter.sourceforge.net/) can be used
instead. The switchPlotfun function can be used to switch
the plotting back-end. Available arguments are ks2paint and
haplopaint for kinship2 and
HaploPainter plotting, respectively. Note however, that
HaploPainter only allows to export plots to a file, while
kinship2 plotting allows, in addition to export the plot,
also to show it as a standard R plot.
Below we use the switchPlotfun to ensure the use of
kinship2 plotting (usually not required) and plot the full
available pedigree of individual 3. If the age of
individuals is available, it will be plotted below the individual’s
ID.
switchPlotfun("ks2paint")
## By supplying device="plot", we specify that we wish to visualize the
## pedigree in an R plot. This is the default for "ks2paint", anyway.
plotPed(fad, id = 3, device = "plot")
The pedigree for an individual or a list of individuals can be
extracted using the buildPed method. By default the method
first tries to identify all parents up to 3 generations in the pedigree,
and subsequently all children of the individuals and all identified
parents.
## [1] 29Alternatively, we can extract the smallest possible pedigree for a
list of individuals by specifying prune=TRUE. Internally,
the function transforms the pedigree into a graph, tries to find all
paths between the individuals and returns the sub-graph of all
individuals along with individuals along the paths between them.
## Find the subpedigree for individuals 21, 22 and 17.
buildPed(fad, id = c(21, 22, 17), prune = TRUE)## family id father mother sex
## 3 4 3 25 4 F
## 4 4 4 1 2 F
## 1 4 1 NA NA M
## 8 4 8 1 2 F
## 17 4 17 28 8 M
## 21 4 21 24 3 M
## 22 4 22 24 3 F
## 2 4 2 NA NA F
## 25 4 25 NA NA M
## 28 4 28 NA NA M
## 24 4 24 NA NA MAnd the pedigree plot for that subset of the whole family:
Note that the pedigree returned by the buildPed method
for an individual might be different than the pedigree of a whole
family. The pedigree returned by buildPed contains only
individuals that share kinship with the specified individual. To
exemplify this, we plot the pedigree for the family 14 in
the Minnesota Breast Cancer data set. Note that the individuals in the
pedigree plot depicted as diamonds are individuals with unknown gender.
(The message “Did not plot…” is issued by the kinship2
plotting function and indicates singletons that are assigned to the
family but do neither have parents nor children.)
## Did not plot the following people: 457 463 470 471 26067 26068 26098 26099In this family, founder 441 is the founder of two family
branches. Building the pedigree for individual 440 will not
include any of the individuals of the second branch, as he does not
share kinship with any of them. The pedigree built for 447
on the other hand contains also individuals from the second branch as
she shares kinship with them (via her mother
441).
## Check if we have individual 26064 from the second branch in the pedigree
## of individual 440.
any(buildPed(fad, id = "440")$id == "26064")## [1] FALSE## [1] TRUEA family pedigree may consist of many founder couples
(i.e. individuals for which neither father nor mother is defined in the
pedigree). To identify the pedigree’s founder couple (being the couple
with the largest number of offspring generations in the pedigree) the
findFounders method can be used. Note that the function
returns always only one couple, even if there might be two founder
couples in the family pedigree with the same number of offspring
generations.
## [1] "1" "2"Alternatively, it might be of interest to determine the closest
common ancestor between individuals in a pedigree. Below we use the
getCommonAncestor method to identify the common ancestor
for individuals 21, 22 and 17
(which we know from the pedigree a bit above are 1 and
2).
## [1] "1" "2"Other useful methods are getChildren,
getAncestors and getSiblings, that return the
children (or all offspring generations up to a specified level), the
parents (or all ancestors) or the siblings for the specified
individuals, respectively.
## [1] "3"## [1] "3" "21" "22" "23"## [1] "1" "2"## [1] "4" "5" "6" "7" "8" "9" "10"In the whole Minnesota Breast Cancer data set there are 426 families corresponding to 426 founders that had cancer during the screening phase between 1944 and 1952. In the code block below we identify the affected founders per family.
## Add the trait information to the FAData object.
cancer <- mbsub$cancer
names(cancer) <- as.character(mbsub$id)
trait(fad) <- cancer
## Identify the affected founders.
## First all affected individuals.
affIds <- affectedIndividuals(fad)
## Identify founders for each family.
founders <- lapply(unique(fad$family), function(z){
return(findFounders(fad, family = z))
})
names(founders) <- unique(fad$family)
## Track the affected founder.
affFounders <- lapply(founders, function(z){
return(z[z %in% affIds])
})
## Interestingly, not all founders are affected! It seems in some cases
## parents of the affected participants in the screening phase have also
## been included.
affFounders <- affFounders[unlist(lapply(affFounders, length)) > 0]
## The number of families analyzed.
length(founders)## [1] 10## [1] 2Unexpectedly, only in few families one of the founders is affected. For the other families additional (unaffected) ancestors might have been added at a later time point.
Next we get the number of affected individuals that are related to these affected founders.
kin2affFounders <- shareKinship(fad, unlist(affFounders))
## How many of these are affected?
sum(kin2affFounders %in% affIds)## [1] 7## [1] 21Pedigree analysis methods
In this section we perform some more advanced pedigree operations.
First, we identify all individuals in the pedigree that share kinship
with individual 4.
## [1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" "12" "13" "14" "15"
## [16] "16" "17" "18" "19" "20" "21" "22" "23"It is also possible to prune remote relatives. If we don’t want to
include grand children, (first) cousins and everbody else more remotely
related to individual 4, we use the option
rmKinship. Essentially, only siblings, children, and
parents remain.
## Get all individuals sharing kinship with individual 4, but only with kinship
## higher than 0.125 (exclude first cousins, grand children, great grand
## parents etc, i.e. everybody with kinship 0.125 or lower)
shareKinship(fad, id = "4", rmKinship = 0.125)## [1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10"Next, we determine generations within the pedigree. Generations can
only be estimated for a single family, since in most instances e.g. the
year of birth is not available. Thus, generations are estimated
considering the relation between individuals, starting from the founder
couple, i.e. generation 0, assigning generation 1 to their children and
all the mates of their children and so on. The
estimateGenerations method calculates such generation
numbers for each family defined in the object (or for a single family,
if the family ID is provided). The result is returned as a list with the
list names corresponding to the family ID and the list elements being
the estimated generation numbers (with names corresponding to the ID of
the respective individual).
## $`4`
## 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
## 0 0 2 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 2 1 1
## 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
## 1 1 1 NA NA NA NA NA NA NA NA NA NA NA NA NA NA
##
## $`5`
## 44 45 46 47 48 49 50 51 52 53 54 55 56
## 0 0 2 2 2 2 2 2 2 2 1 3 3
## 57 58 59 60 61 62 63 64 65 66 67 68 69
## 3 3 3 3 3 3 3 3 2 2 2 NA 2
## 70 71 72 73 74 75 76 77 78 79 26050 26051
## 1 NA NA NA NA NA NA NA NA 2 NA NA
##
## $`6`
## 80 81 82 83 84 85 86 87 88 89 90 91 92
## 0 0 2 2 1 1 1 1 1 1 1 1 1
## 93 94 95 96 97 98 99 100 101 102 103 104 105
## 1 2 2 2 2 2 2 2 3 3 3 3 2
## 106 107 108 109 110 111 112 113 114 115 116 117 118
## 2 1 1 1 NA NA NA NA 2 NA NA NA NA
## 26052 26053
## 3 3Individuals without generation level (i.e. with an NA)
are not connected to any other individual in the pedigree (and thus most
likely represent errors in the pedigree).
In addition, it is also possible to calculate generation levels relative to a (single) specified individual:
We can render these generation numbers into the pedigree:
## Did not plot the following people: 30 31 32 33 34 35 36 37 38 39 40 41 42 43Additional plotting options
If a trait information is available it might be of interest to
highlight affected individuals in the pedigree. Trait information should
always be coded as 0 (or FALSE) for unaffected
and 1 (or TRUE) for affected. In the example
below, we use the cancer information from the Minnesota Breast
Cancer Study.
## Extract the cancer trait information.
tcancer <- mbsub$cancer
names(tcancer) <- mbsub$id
## Set the trait.
trait(fad) <- tcancerWe can now extract the trait information from the object or identify directly the phenotyped or affected individuals.
## 1 2 3 4 5 6
## 0 0 0 1 0 0## [1] "4" "11" "37" "54" "84" "122"## [1] "1" "2" "3" "4" "5" "6"Plotting a FAData object with trait information results
in a pedigree plot with highlighted affected individuals (for
kinship2 pedigree plotting: affected, unaffected and not
phenotyped are represented as filled symbols, open symbols and symbols
with a question mark inside, respectively).
## Did not plot the following people: 200 204 206 210 212 214 215 216 217 219In addition, we can manually highlight individuals using the
highlight.ids argument. For kinship2 pedigree
plotting, a list of length 2 is supported as argument
highlight.ids, with the first element being plotted on the
top left corner of the symbol and the second element on the top right
corner.
## Plotting the pedigree for family "9".
plotPed(fad, family = "9", highlight.ids = list(a = c("185", "201", "198"),
b = c("193")))
## Did not plot the following people: 200 204 206 210 212 214 215 216 217 219An alternative way to highlight individuals or add text to the plot
is to use the arguments label1, label2 and
label3 or the plotPed method.
Graph utilities
Pedigrees can also be transformed to graphs using the
ped2graph function. That way all graph theory methods
implemented in e.g. the igraph package can be applied to
pedigrees.
## Transform the full pedigree to a graph.
fullGraph <- ped2graph(pedigree(fad))
## In addition, build the graph for a single family.
singleFam <- ped2graph(family(fad, family=4))We can plot these pedigrees also as graph and could use any of the
layout methods provided in the igraph package.
Pedigrees represented as graphs.
Pedigrees represented as graphs.
The connectedSubgraph function implemented in the
FamAgg package provides additional functionality to find
the smallest connected subgraph of a list of submitted nodes
(i.e. individuals).
In the code below we want to extract the smallest possible connected
subgraph of the pedigree-graph of family 4 containing individuals
7, 8, 27 and 17.
This is in principle what the buildPed method with the
option prune=TRUE does to find the smallest pedigree for a
set of individuals, only that buildPed ensures that also
eventually missing parents are added.
## Similar to buildPed/plotPed with prune=TRUE.
plotPed(fad, id=c("7", "8", "17", "27"), prune=TRUE)## Removing singletons... none present.
Importing and exporting pedigree data
Besides providing the pedigree data as a data.frame, the
FAData constructor can also read pedigree data from various
file formats, such as plink [4]
ped or fam files (http://pngu.mgh.harvard.edu/~purcell/plink/data.shtml)
or generic text files.
## Import a "ped" file.
pedFile <- system.file("txt/minnbreastsub.ped.gz", package = "FamAgg")
## Quick glance at the file.
readLines(pedFile, n = 1)## [1] "4\t1\t0\t0\t1\t1"## family id father mother sex
## 1 4 1 <NA> <NA> M
## 2 4 2 <NA> <NA> F
## 3 4 3 25 4 F
## 4 4 4 1 2 F
## 5 4 5 1 2 M
## 6 4 6 1 2 MAlternatively, we can import pedigree data from generic input files.
## Create the FAData by reading data from a txt file.
pedFile <- system.file("txt/minnbreastsub.txt", package = "FamAgg")
fad <- FAData(pedigree = pedFile, header = TRUE, id.col = "id",
family.col = "famid", father.col = "fatherid",
mother.col = "motherid")And we can export pedigree data again using the export
method. In the example below, we subset the whole pedigree to the
pedigree of family 4 and export this as a ped file.
Testing for familial aggregation
Familial aggregation aims to identify families within large ancestral pedigrees that show a non-random aggregation of traits.
As an example, we analyze here data from the Minnesota Breast Cancer
Record, which is provided by the kinship2 package. In
brief, this data set consists of genealogical information from 426
unrelated founders diagnosed with breast cancer whose families entered a
longitudinal study on cancer in the state of Minnesota (USA) in 1944.
Cancer cases are encoded with a 1 in column
cancer in the minnbreast
data.frame. Note however that, besides breast cancer, also
prostate cancer cases are reported. This unfortunately causes a
systematic bias in the data set as families were only included if a
founder was diagnosed with breast cancer, but all occurrences of both
breast and prostate cancer are reported. Based on this bias many of the
results below should be taken with caution. Another important
information is provided in column endage, which represents
either the age of cancer onset, the age at the end of the study or the
age at death of the participant.
Note that, to reduce computation time, we perform the analysis only
on a subset of families from the Minnesota Breast Cancer record and
reduce the number of simulation runs. We specifically selected some
families with a high percentage of cancer cases, thus, the analysis
presented here is biased. Also, in a real analysis you should increase
the nsim argument.
library(FamAgg)
set.seed(18011977)
data(minnbreast)
## Subset the dataset to reduce processing time.
mbsub <- minnbreast[minnbreast$famid %in% c(4:100, 173, 432), ]
## Uncomment the line below to use the whole dataset instead.
## mbsub <- minnbreast
## Define the number of simulations we perform.
## nsim <- 10000
nsim <- 1000
mbped <- mbsub[, c("famid", "id", "fatherid", "motherid", "sex")]
## Renaming column names.
colnames(mbped) <- c("family", "id", "father", "mother", "sex")
## Create the FAData object.
fad <- FAData(pedigree = mbped)
## Define the trait.
tcancer <- mbsub$cancer
names(tcancer) <- as.character(mbsub$id)In the following section we analyze the data set first using the genealogical index method [5] (Section 4.1), then we estimate the per-individual risk of disease using the familial incidence rate (FIR, also abbreviated as FR in the original work) [6] (Section 4.2) and apply our kinship sum test to identify affected individuals exhibiting a higher relationship to other affected individuals than what would be expected by chance (Section 4.3). Subsequently, we apply our kinship group test (Section 4.4) that allows to identify highly clustered affected individuals within families.
The genealogical index of familiality and the familial incidence rate test are well established methods while the kinship sum test and the kinship group test are novel approaches presented here for the first time.
Genealogical index of familiality
We next calculate the genealogical index of familiality (GIF) [5] (referred to as the genealogical index in the original work) for cancer occurrence in a subset of the Minnesota Breast Cancer Record data set. For a given trait (e.g. whether or not an individual was diagnosed with a certain type of cancer), the method computes the mean kinship between affected individuals (cases) in the whole pedigree along with mean kinship values of randomly drawn sets of individuals. The distribution of average kinship values among the control sets is then used to estimate the probability that the observed level of kinship among the cases is due to chance.
Below, we perform the analysis using the
genealogicalIndexTest method on the cancer
trait. In its default setting, the genealogicalIndexTest
function uses all phenotyped individuals in the pedigree as control
population from which sets of random samples equal in size to the number
of affected are drawn.
Note that by default the function excludes all singletons
(i.e. unconnected individuals in the pedigree) from the analysis.
Changing the argument rm.singletons to FALSE
will estimate the GIF on the full data set.
## Calculate the genealogical index of familiality.
gi <- genealogicalIndexTest(fad, trait = tcancer,
traitName = "cancer", nsim = nsim)
## Display the result.
result(gi)## trait_name total_phenotyped total_affected entity_id entity_ctrls
## 1 cancer 3508 248 1 2804
## entity_affected genealogical_index pvalue padj
## 1 214 192.5102 0.001 0.001The column genealogical index of the result
data.frame shown above represents the mean kinship between
all pairs of affected individuals in the pedigree multiplied by
100000 for easier interpretation. Thus, according to the
GIF test, a clustering of cancer cases is present in the analyzed
pedigree. The output messages from the method call indicate that some
individuals have been excluded from the test since they were either not
phenotyped in the trait (i.e. have a missing value in trait), or are not
connected in the family pedigree (do not share kinship with any
other individual in the pedigree after removing non-phenotyped
individuals).
The genealogical index of familiality implementation in this package
adds some more flexibility to the original approach. The definition of
the appropriate set of control individuals from which random samples are
drawn can be specified with the controlSetMethod argument.
Also, it is possible to perform a stratified sampling, e.g. if the group
of affected cases in a pedigree consists of 5 female and 3 male
individuals, submitting the sex of each individual in the pedigree with
the argument strata (i.e. strata=fad$sex, with
fad being the FAData object on which the
analysis is performed) allows the function to define random control sets
with the same proportion of male/female individuals.
In the next example, we use the getSexMatched function
to define the set of control individuals and also the
getExternalMatched submitting the gender information of
each individual. The results from both approaches are essentially
identical, and in the present data set not that useful, as the Minnesota
Breast Cancer data set lists both, breast cancer and prostate cancer in
column cancer, thus, the set of control individuals will
contain all individuals with known sex.
## Calculate the genealogical index of familiality using random sampling from
## a sex matched control set.
giSexMatch <- genealogicalIndexTest(fad, trait = tcancer,
traitName = "cancer", nsim = nsim,
controlSetMethod = "getSexMatched")
## Use an external vector to perform the matching.
## The results are essentially identical.
giExtMatch <- genealogicalIndexTest(fad, trait = tcancer,
traitName = "cancer", nsim = nsim,
controlSetMethod = "getExternalMatched",
match.using = fad$sex)Note that any matching or stratified sampling can lead to the exclusion of individuals with missing values in either the matching criteria or the strata.
In the Minnesota Breast Cancer data set, the number of prostate cancer cases is much lower than the number of breast cancer cases, thus, simple random sampling might result in an biased genealogical index of familiality estimate since about the same proportion of male and female individuals will be sampled. To account for such cases a stratified sampling, as performed below, can be used instead.
##
## M F
## 39 206## We can use the gender information to perform stratified sampling, i.e.
## in each permutation a random set of 3 male and 15 females will be selected.
giStrata <- genealogicalIndexTest(fad, trait = tcancer,
traitName = "cancer", nsim = nsim,
strata = fad$sex)
result(giStrata)## trait_name total_phenotyped total_affected entity_id entity_ctrls
## 1 cancer 3508 248 1 2801
## entity_affected genealogical_index pvalue padj
## 1 214 192.5102 0.001 0.001Finally, we plot the result from the simulation. The blue vertical line in the plot below represents the mean kinship value between all affected individuals in the pedigree. The distribution of mean kinship values from the 1000 randomly drawn sets are shown in grey color.
The genealogical index of familiality can also be estimated by the
gif function from the gap R-package. Below we
calculate the estimate using both methods and compare the resulting
estimate. Note that the gif method reports only the
genealogical index of familiality estimate but does not estimate
significance.
library(gap)
## Adding the trait information, so the extracted pedigree data.frame will
## also contain a column "affected" with that information.
trait(fad) <- tcancer
## Extract the pedigree and re-format it for the gif function.
pedi <- pedigree(fad)
## Remove singletons.
pedi <- removeSingletons(pedi)
pedi[is.na(pedi$father), "father"] <- 0
pedi[is.na(pedi$mother), "mother"] <- 0
## Identify the affected individuals.
affIds <- as.numeric(pedi$id[which(pedi$affected == 1)])
## Execute the gif method contained in the gap package.
gifRes <- gif(pedi[, c("id", "father", "mother")], affIds)
## Calculate the GIF using FamAgg's genealogicalIndexTest.
gifT <- genealogicalIndexTest(fad, trait = tcancer, nsim = 100)
## Comparing the results:
all.equal( result(gifT)$genealogical_index, gifRes[[1]] )## [1] TRUEThus, the GIF estimate from the gap package is identical
to the one from the FamAgg package.
In the examples above, we tested for an enrichment of cancer cases in
the full data set, i.e. across all families. In addition, we can perform
the test individually for each family, by setting the
perFamilyTest parameter of the
genealogicalIndexTest to TRUE, and thus test
for a clustering of cancer cases within each family.
## Perform the analysis (no strata etc) separately for each family.
giFam <- genealogicalIndexTest(fad, trait = tcancer, nsim = nsim,
perFamilyTest = TRUE,
traitName = "Cancer")
## Display the result from the analysis.
head(result(giFam))## trait_name total_phenotyped total_affected entity_id entity_ctrls
## 13 Cancer 3508 248 13 29
## 432 Cancer 3508 248 432 106
## 14 Cancer 3508 248 14 31
## 89 Cancer 3508 248 89 78
## 30 Cancer 3508 248 30 25
## 40 Cancer 3508 248 40 39
## entity_affected genealogical_index pvalue padj
## 13 5 21250.000 0.001 0.0510
## 432 15 9940.476 0.002 0.0510
## 14 5 21250.000 0.003 0.0510
## 89 5 15625.000 0.028 0.3315
## 30 3 25000.000 0.037 0.3315
## 40 3 20833.333 0.039 0.3315Familial incidence rate (FIR)
A per-individual risk of e.g. disease can be calculated using the familial incidence rate (FIR, abbreviated as FR in the original work) [6]. This measure considers the kinship of each individual with any affected in a given trait in the pedigree and the time at risk for each individual. Thus, the FIR is an estimate for the risk per gene-time for each individual given the disease-experience in the cohort.
As time at risk for each individual we use the
endage column in the Minnesota Breast Cancer data set,
which represents the participant’s age at the last follow-up or at
cancer incidence. This estimate of time at risk is rather crude and in a
real life situation a better, more accurate, estimate that is based
e.g. on the birth dates and dates of last follow up or incidence might
be used instead. See the help of functions
estimateTimeAtRisk and sliceAge for details
and options related to time at risk.
## Estimate the risk for each individual using the familial incidence
## rate method. We use the "endage" provided in the Minnesota Breast Cancer
## Record as a measure for time at risk.
fr <- familialIncidenceRate(fad, trait = tcancer, timeAtRisk = mbsub$endage)A note on singletons: for all per-individual measures unconnected
individuals within the pedigree are automatically excluded from the
calculations as no kinship-based statistics can be estimated for them
(they do, by definition, not share kinship with any other individual in
the pedigree, thus their kinship coefficient with any other individual
in the pedigree will be 0). Note also that the removal of
e.g. not phenotyped individuals prior to the calculation can also
generate singletons, that additionally become removed. This
removal results in an estimate with the value NA for all
singletons as well as not phenotyped individuals.
Next, we calculate the mean FIR within each family and plot this information.
## Split the FIR by family and average the values within each.
frFam <- split(fr, f = fad$family)
frFamAvg <- lapply(frFam, mean, na.rm = TRUE)
## Sort and plot the averages.
frFamAvg <- sort(unlist(frFamAvg), decreasing = TRUE)
plot(frFamAvg, type = "h", xaxt = "n", xlab = "", ylab = "mean FIR",
main = "Per family averaged familial incidence rate")
axis(side = 1, las = 2, at = 1:length(frFamAvg), label = names(frFamAvg))
Not unexpectedly, individuals in some families have on average a higher familial incidence rate, and thus a higher risk of cancer than others.
In the next example, we calculate the familial incidence rate assessing in addition the significance of each estimate using Monte Carlo simulations. This extension to the original approach from Kerber [6] does also allow stratified sampling.
## Estimate the risk for each individual using the familial incidence
## rate method. We use the endage provided in the Minnesota Breast Cancer
## Record as a measure for time at risk.
frTest <- familialIncidenceRateTest(fad, trait = tcancer,
traitName = "cancer",
timeAtRisk = mbsub$endage,
nsim = nsim)The familial incidence rate can be extracted easily from the result
object using the familialIncidenceRate method or using
$fir. Also, the empirical p-value from the simulation
analysis and the time at risk can be accessed using the $
operator (i.e. using $pvalue, $tar or
$timeAtRisk, respectively).
## 1 2 3 4 5 6
## NA 0.002278208 0.002365165 0.000670492 0.002709228 0.002098398## 1 2 3 4 5 6
## NA 0.002278208 0.002365165 0.000670492 0.002709228 0.002098398Finally, we inspect the results from the analysis.
## trait_name total_phenotyped total_affected total_tested id family
## 3185 cancer 3508 248 1778 3185 77
## 7122 cancer 3508 248 1778 7122 173
## 7125 cancer 3508 248 1778 7125 173
## 7123 cancer 3508 248 1778 7123 173
## 7124 cancer 3508 248 1778 7124 173
## 7121 cancer 3508 248 1778 7121 173
## fir pvalue padj
## 3185 0.015789474 0 0
## 7122 0.010449918 0 0
## 7125 0.008874950 0 0
## 7123 0.008848773 0 0
## 7124 0.008587047 0 0
## 7121 0.008249860 0 0We can also identify the families containing individuals with a significant FIR.
frRes <- result(frTest)
frSig <- frRes[which(frRes$padj < 0.05), ]
## Split by family.
frFam <- split(frSig, frSig$family)
frRes <- data.frame(family = names(frFam),
no_sign_fir = unlist(lapply(frFam, nrow)))
## Determine the number of phenotyped and affected individuals per family.
noPheNAff <- sapply(names(frFam), function(z){
fam <- family(frTest, family = z)
return(c(no_pheno = sum(!is.na(fam$affected)),
no_aff = length(which(fam$affected == 1))
))
})
frRes <- cbind(frRes, t(noPheNAff))
## Display the number of phenotyped and affected individuals as well as
## the number of individuals within the families with a significant FIR.
frRes[order(frRes[, "no_sign_fir"], decreasing = TRUE), ]## family no_sign_fir no_pheno no_aff
## 432 432 12 123 15
## 173 173 8 35 10
## 77 77 1 68 5We have an enrichment of affected cases in families 173, 13 and 432.
Kinship sum test
Next, we use the kinship sum test that evaluates familial
aggregation based on the sum of kinship values between affected cases.
The test identifies affected individuals exhibiting a higher
relationship to other affected individuals than would be expected by
chance. By specifying the strata we perform sex-stratified
random sampling, i.e. ensure that the proportion of male and female
individuals in each randomly sampled group matches the corresponding
proportions in the real, observed, affected.
## Perform the kinship sum test.
kinSum <- kinshipSumTest(fad, trait = tcancer, traitName = "cancer",
nsim = nsim, strata = fad$sex)
head(result(kinSum))## trait_name total_phenotyped total_affected affected_id family affected
## 17528 cancer 3508 248 17528 432 245
## 17517 cancer 3508 248 17517 432 245
## 17529 cancer 3508 248 17529 432 245
## 17547 cancer 3508 248 17547 432 245
## 17548 cancer 3508 248 17548 432 245
## 17549 cancer 3508 248 17549 432 245
## ksgrp kinship_sum freq pvalue padj
## 17528 1 2.00 0.0004081633 5.714286e-05 0.004714286
## 17517 1 1.75 0.0040816327 1.346939e-04 0.004714286
## 17529 1 1.75 0.0040816327 1.346939e-04 0.004714286
## 17547 1 1.75 0.0040816327 1.346939e-04 0.004714286
## 17548 1 1.75 0.0040816327 1.346939e-04 0.004714286
## 17549 1 1.75 0.0040816327 1.346939e-04 0.004714286Next, we identify those individuals that have a significant kinship sum accepting a 10% false discovery rate (FDR).
## Extract the IDs of the individuals with significant kinship. By default,
## the raw p-values are adjusted for multiple hypothesis testing using the
## method from Benjamini and Hochberg.
kinSumRes <- result(kinSum)
kinSumIds <- as.character(kinSumRes[kinSumRes$padj < 0.1, "affected_id"])
## From which families are these?
table(kinSumRes[kinSumIds, "family"])##
## 173 432
## 6 12Thus, most of the identified significant individuals are from two families. Next, we compare the FIR scores of affected or unaffected (but phenotyped) individuals in this family to the FIR scores of affected or unaffected individuals of all other families.
## Get the familial ratio of the significant in this family, of all in
## this family, and of all others.
famId <- kinSumRes[1, "family"]
## Extract the family.
fam <- family(kinSum, family = famId)
## Stratify individuals in affected/unaffected.
strat <- rep("All, unaff.", length(kinSum$id))
strat[which(kinSum$affected > 0)] <- "All, aff."
strat[kinSum$id %in% fam$id] <- paste0("Fam ", famId, ", unaff.")
strat[kinSum$id %in% fam$id[which(fam$affected > 0)]] <-
paste0("Fam ",famId,", aff.")
famData <- data.frame(fr = fr, group = strat)
boxplot(fr~group, data = famData, na.rm = TRUE, ylab = "FIR",
col = rep(c("#FBB4AE", "#B3CDE3"), 2))
As expected, the familial incidence rate (i.e., in the present data set, the risk of individuals to get cancer, given their kinship to other cancer cases) for individuals (whether affected or yet unaffected) in this family is higher than in the data set analyzed here.
Next, we plot the pedigree of this family.
## Plot the pedigree for the family of the selected individual removing
## all individuals that were not phenotypes.
plotPed(kinSum, id = kinSumIds[1], cex = 0.3, only.phenotyped = TRUE)
And finally, also plot the kinship sum for the individuals with the largest kinship sum in relation to the expected kinship sums from the Monte Carlo simulations.
Kinship group test
Here we apply the kinship group test to the data set. This test first defines for each affected individual a group of individuals considering only individuals that are as closely related as the most distant affected individual. For each of these kinship groups two tests are then performed, one by comparing the mean kinship among affected in the group with the mean kinship from Monte Carlo simulations (ratio test) and one evaluating the largest observed kinship value between affected individuals with those of random samples from the simulation (kinship group test).
In the example below we specify again the strata
argument and thus perform sex-stratified random sampling.
## Calculate the kinship test.
kinGroup <- kinshipGroupTest(fad, trait = tcancer,
traitName = "cancer",
nsim = nsim, strata = fad$sex)
head(result(kinGroup))## trait_name total_phenotyped total_affected phenotyped affected group_id
## 410 cancer 3508 248 1147 174 410
## 2984 cancer 3508 248 1147 174 2984
## 17609 cancer 3508 248 1147 174 17609
## 7117 cancer 3508 248 1147 174 7117
## 17517 cancer 3508 248 1147 174 17517
## 17547 cancer 3508 248 1147 174 17547
## family group_phenotyped group_affected ratio_pvalue ratio_padj
## 410 13 8 5 0 0
## 2984 72 1 2 0 0
## 17609 432 6 5 0 0
## 7117 173 19 8 0 0
## 17517 432 53 13 0 0
## 17547 432 55 14 0 0
## mean_kinship kinship_pvalue kinship_padj
## 410 0.2500000 0 0
## 2984 0.2500000 0 0
## 17609 0.2500000 0 0
## 7117 0.1607143 0 0
## 17517 0.1458333 0 0
## 17547 0.1346154 0 0The kinship group test finds a significant aggregation of cases in families 13, 72, 173 and 432. In fact, as we see further below, the test identified a subgroup in the latter which shows with an exceptional high proportion of cases.
Below, we summarize the results further by listing the total number of families in the pedigree and the number of families in which kinship groups with significant kinship p-value and significant ratio p-value (both at a 5% FDR).
kinGroupRes <- result(kinGroup)
## Create a data.frame with the summarized results.
resTab <- data.frame(total_families = length(unique(kinGroup$family)),
ratio_sign = length(unique(
kinGroupRes[kinGroupRes$ratio_padj < 0.05, "family"]
)),
kinship_sign = length(unique(
kinGroupRes[kinGroupRes$kinship_padj < 0.05, "family"]
))
)
resTab## total_families ratio_sign kinship_sign
## 1 69 6 9The most significant kinship group identified by the kinship group
test is shown in the figure below. The mother (individual
17609) of the nuclear family representing this group and
all her daughters have cancer (see figure below). This mother is however
not directly related to the affected founder of this family, individual
17517, but did marry her son (id 17530; see
figure above for the full pedigree of this family 432).
We are also submitting the familial incidence rate values calculated
above with argument label1 which are then displayed below
the ID of each individual in the plot.
plotPed(kinGroup, id = kinGroupRes[kinGroupRes$family == "432",
"group_id"][1],
prune = TRUE, label1 = fr)
Binomial test
The binomial test evaluates whether the number of affected in a
family (or the whole pedigree) is significantly higher than what would
be expected by chance (given a probability of being affected in a
trait). In contrast to most other methods this test does not take the
degree of kinship between individuals into account and is hence
independent of the family structure in the pedigree. We can perform this
type of test using the binomialTest function on any
FAData object or any object extending it. Below we use the
binomial test to evaluate a significant enrichment of affected
individuals in any family in the pedigree.
binRes <- binomialTest(fad, trait = tcancer, traitName = "Cancer")
binResTab <- result(binRes)
head(binResTab)## trait_name total_phenotyped total_affected family phenotyped affected
## 173 Cancer 3508 248 173 35 10
## 19 Cancer 3508 248 19 24 5
## 432 Cancer 3508 248 432 123 15
## 94 Cancer 3508 248 94 36 6
## 8 Cancer 3508 248 8 37 6
## 14 Cancer 3508 248 14 32 5
## pvalue prob padj
## 173 0.0001101636 0.07069555 0.007601286
## 19 0.0241694261 0.07069555 0.603487360
## 432 0.0273283250 0.07069555 0.603487360
## 94 0.0388827384 0.07069555 0.603487360
## 8 0.0437309681 0.07069555 0.603487360
## 14 0.0720884731 0.07069555 0.766407020The probability used on the binomial test is shown in column
"prob" and is in essence the ratio between the affected and
phenotyped in the pedigree (i.e. 154/2202). This might be an
overestimation, especially if the provided pedigree is not
representative of the population. A population-based probability can
however be provided with argument prob. Below we test
specifically whether we have families in which the number of individuals
with breast cancer is significantly higher than expected. To this end we
set the trait status of all male individuals to NA and
repeat the test providing the probability of developing breast cancer
during in women, which, according to the U.S. Breast Cancer Statistics
(from breastcancer.org) is 1 out of 8 in their life time.
## Set the trait status to NA for all male individuals.
tcancer[fad$sex == "M" | is.na(fad$sex)] <- NA
## Perform the test providing also the population probability
binRes <- binomialTest(fad, trait = tcancer, prob = 1/8)
binResTab <- result(binRes)
head(binResTab)## trait_name total_phenotyped total_affected family phenotyped affected
## 14 NA 1990 206 14 15 5
## 19 NA 1990 206 19 12 4
## 13 NA 1990 206 13 18 5
## 94 NA 1990 206 94 18 5
## 8 NA 1990 206 8 19 5
## 173 NA 1990 206 173 19 5
## pvalue prob padj
## 14 0.03107294 0.125 0.9090792
## 19 0.05281048 0.125 0.9090792
## 13 0.06464965 0.125 0.9090792
## 94 0.06464965 0.125 0.9090792
## 8 0.07905037 0.125 0.9090792
## 173 0.07905037 0.125 0.9090792Below we plot the pedigree for the family with the strongest enrichment with affected individuals.
## Warning in kinship2::pedigree(id = individual, dadid = father, momid = mother,
## : More than 25% of the gender values are 'unknown'
## Did not plot the following people: 7135 7141 7143 7144 7145 7146 7148 7149 26800 26811 26812 26813