In TheJacksonLaboratory/mousegwas: Run in-bred mouse GWAS

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
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library(mousegwas)

This package was built for easier deployment of GWAS in mouse panels. Several mouse panels have been genotyped using different arrays like the Mouse Diversity Array (MDA) or the GigaMUGA (GMUGA), a lot of which are available through The Jackson Laboratory Mouse Phenome Database (MPD: https://phenome.jax.org/about/snp_retrievals_help). This package use the genotyping downloaded from MPD to run GWAS on mouse phenotypes using GEMMA or pyLMM and plot the results.

Data preparation

The phenotypes should be given as a csv file with at least one column to define the strain and other columns for the phenotypes and the covariates, a companion yaml file will describe the input data.

The yaml file

The yaml file should contain the following data:

• phenotypes: A dictionary of dictionaries describing the phenotypes to test, their name in the figures and the group, if desired. e.g.:

phenotypes:
  OFA_Groom_first5m:
      papername: GrTime5m
      group: Grooming Quantity

• strain: The name of the column containing the strain name. e.g.:

strain: Strain

• groups: A list of groups for combining p-values in the post-processing. The order will define their order in the plots. e.g.:

groups:
  - Activity
  - Anxiety
  - Grooming Pattern
  - Grooming Quantity

• F1: A list of lists translating F1 strain names in the input csv file to their parent strains. The mother's strain should be the first in the list to determine the X chromosome e.g.:

F1:
  - B6129SF1/J:
      - C57BL/6J
      - 129S1/SvImJ
  - B6129PF1/J:
      - C57BL/6J
      - 129P3/J
  - B6AF1/J:
      - C57BL/6J
      - A/J

• covar: A list of covariate columns in the input file, e.g.:

covar:
  - Sex
  - BodyLength

• sex: The column containing the sex data, used for down-sampling individuals from each strain. e.g.:

sex: Sex

• translate: If names of strains in the input csv file are different than the strain names in the genotyping file you can use this dictionary to translate it. You can also use this to remove certain strains from the analysis. e.g.:

translate:
  - BTBRT...tf.J: BTBR T<+> Itpr3<tf>/J
  - 129S1.SvImJ: 129S1/SvImJ
  - MSM/MsJ: none
  - MOLF/EiJ: none

• coat: This feature is optional and can be used to use the coat color as a covariate or as a phenotype, mainly good for testing. e.g.:

coat:
  - 129P3/J: albino
  - 129S1/SvImJ: white-bellied agouti
  - 129X1/SvJ: albino

*confSNPs: Confounding SNPs. A list of SNPs that will be used as covariates in the GWAS. This is useful to remove a massive selection factor. e.g.:

confSNPs:
  - rs32105080

Running GWAS

The script for running the GWAS is called run_GWAS.R

data preprocessing

Mouse panel GWAS is different than human GWAS, the LD blocks are wider, the population structure is biased and the individuals are usually homozygous. It is unclear how many individuals from each strain should be included in the analysis so we implemented an option to select a defined number of individuals from each Strain x Sex combination or to get the average value of each strain while controlling for the covariates by taking the residuals of a linear model solving each phenotype with the covariates.

This option can be specified using the parameter --downsample or -d with the number of individuals to select from each Strain x Sex group or 0 for average.

If the input table contains strain names that are different than the names in the genotypes table then a translation dictionary can be given in the yaml file (phenotype -> genotype). When F1 strains are phenotyped then names of the parent strains should be specified in the yaml file under the F1 term, the female parent should be the first one to determine the X chromosome.

After the table of phenotypes is ready for the individuals that will be used in the GWAS, the values are being scaled to have a mean of zero and variance of one. A quantile-quantile normalization is also optional with the --qqnorm option. Boolean phenotypes are not being scaled.

SNPs filtering

SNPs can be filtered using the parameters --missing for the minimal fraction of missing data and --MAF for the minimal allele frequency threshold.

LMM software

By default the software for running the GWAS will be GEMMA, if it is not available it will be downloaded. The model will be LMM with all tests (-lmm 4). pyLMM is also an option and can be selected with -m pyLMM or --method pyLMM, although pyLMM should be installed independently, if the executables are not available in the default path they can be given using --pylmm/-p pylmmGWAS.py and --pylmmkinship/-k pylmmKinship.py.

Multivariate analysis

Multivariate GWAS is implemented in GEMMA and can be used by specifying the groups of the phenotypes in the yaml file. Multivariate will be used by default on top of the univariate analysis unless disabled with --nomv.

Combining results

If multiple penotypes are being tested, their results can be combined with meta-analysis. The meta-analysis algorithm used here is METASOFT. Care should be taken when using METASOFT as it assumes the beta factors have the same signs. If two phenotypes are anti-correlated then their p-values will not be combined, only the strongest will eventually be used for the combined p-values. Deploying METASOFT can be done with h --runmetaasoft. After running METASOFT the lambda_mean and lambda_hetero scaling parameters can be obtained from the log file and given back using the --labmda_mean and --lambda_hetero parameters.

Using coat color

Coat colors defined in the yaml file can be used either as covariates with --coat_covar or as phenotypes with --coat_phenotype in which case no input file should be given. Another option to consider coat color as covariates is by specifying the SNPs in coat color determining genes using the confSNPs feature in the yaml file.

Shuhffling

If the --shuffle option is selected, the phenotypes values will be shuffled among all input individuals and the GWAS will be carried on as normal after that. Make sure to change --seed to avoid running the same shuffling more than once when trying to obtain an empirical p-value.

Plotting and post-processing

The plotting part was adjusted for publication and can be changed as desired. It can be used with the postprocess_mv.R script with the output directory of run_GWAS.R as input (--outdir or -o) and the directory to put the figures in (--plotdir or -p).

Manhattan plots

First, the script will plot simple Manhattan plots with the threshold for significant SNP as defined by --pvalthr ($-log_{10}(\tt P-value))$). To remove SNPs in the same LD blocks, correlated SNPs are removed after the best SNP is selected, the correlation threshohld ($r^{2}$) can be changed with --peakcorr, width of the peak region is limited by --ldpeakdist given as mega base-pairs (Mbp).

Grouping parameters

Each parameter can be assigned a group. All phenotypes in a group can be combined together and ran as a multivariate GWAS in run_GWAS.R if used without --nomv. Another option to combine phenotypes is to take the minimal p-value of each SNP across all phenotypes in the group. This can be done by applying the --nomv flag when running postprocess_mv.R. It will also add a Manhattan plot that combines all of the phenotypes.

clustering peaks

After the peaks were selected for each phenotype, all the peak SNPs from all of the phenotypes are being collected and the p-values of these SNPs in all the phenotypes are used for clustering the peaks using k-means algorithm. The number of clusters can be set using the --clusters option and is defaulted for seven clusters. Each cluster gets its own color, the p-values table is being plotted as a heatmap along with the cluster colors. After assigning clusters for the peak SNPs, the Manhattan plots are being repainted with the cluster colors. NPSs correlated to the peak SNP will get the same color and their transparency will be proportional to the correlation coefficient.

TheJacksonLaboratory/mousegwas documentation built on Sept. 27, 2021, 9:14 a.m.