The GTEx Portal API V2 enables programmatic access to data available from the Genotype-Tissue Expression Portal. The gtexr package wraps this API, providing R functions that correspond to each API endpoint:
get_service_info()
.get_maintenance_message()
(corresponding to the endpoint “Get
Maintenance Message”) are page
and
itemsPerPage
. For query parameters that accept an array of
values however, the corresponding function argument is pluralised to
indicate this e.g. for endpoint “Get
Eqtl Genes” the query parameter ‘tissueSiteDetailId’ is pluralised
to argument name tissueSiteDetailIds
in
get_eqtl_genes()
.?get_eqtl_genes
provides example valid values
for the required argument tissueSiteDetailIds
.tibble::tibble
.Users can try out all functions interatively with the ⭐gtexr shiny app⭐, which pre-populates query parameters with those for the first working example from each function’s documentation.
The rest of this vignette outlines some example applications of gtexr.
get_variant(snpId = "rs1410858") |>
tidyr::separate(
col = b37VariantId,
into = c(
"chromosome",
"position",
"reference_allele",
"alternative_allele",
"genome_build"
),
sep = "_",
remove = FALSE
) |>
select(snpId:genome_build)
#>
#> ── Paging info ─────────────────────────────────────────────────────────────────
#> • numberOfPages = 1
#> • page = 0
#> • maxItemsPerPage = 250
#> • totalNumberOfItems = 1
#> # A tibble: 1 × 7
#> snpId b37VariantId chromosome position reference_allele alternative_allele
#> <chr> <chr> <chr> <chr> <chr> <chr>
#> 1 rs1410858 1_153182116… 1 1531821… C A
#> # ℹ 1 more variable: genome_build <chr>
Use get_gene()
or get_genes()
get_genes("CRP") |>
select(geneSymbol, gencodeId)
#>
#> ── Paging info ─────────────────────────────────────────────────────────────────
#> • numberOfPages = 1
#> • page = 0
#> • maxItemsPerPage = 250
#> • totalNumberOfItems = 1
#> # A tibble: 1 × 2
#> geneSymbol gencodeId
#> <chr> <chr>
#> 1 CRP ENSG00000132693.12
Use get_variant()
get_variant(snpId = "rs1410858") |>
select(snpId, variantId)
#>
#> ── Paging info ─────────────────────────────────────────────────────────────────
#> • numberOfPages = 1
#> • page = 0
#> • maxItemsPerPage = 250
#> • totalNumberOfItems = 1
#> # A tibble: 1 × 2
#> snpId variantId
#> <chr> <chr>
#> 1 rs1410858 chr1_153209640_C_A_b38
Use get_significant_single_tissue_eqtls()
(note this
requires versioned GENCODE IDs)
gene_symbol_of_interest <- "CRP"
gene_gencodeId_of_interest <- get_genes(gene_symbol_of_interest) |>
pull(gencodeId) |>
suppressMessages()
gene_gencodeId_of_interest |>
get_significant_single_tissue_eqtls() |>
distinct(geneSymbol, gencodeId, tissueSiteDetailId)
#>
#> ── Paging info ─────────────────────────────────────────────────────────────────
#> • numberOfPages = 1
#> • page = 0
#> • maxItemsPerPage = 250
#> • totalNumberOfItems = 93
#> # A tibble: 3 × 3
#> geneSymbol gencodeId tissueSiteDetailId
#> <chr> <chr> <chr>
#> 1 CRP ENSG00000132693.12 Thyroid
#> 2 CRP ENSG00000132693.12 Esophagus_Gastroesophageal_Junction
#> 3 CRP ENSG00000132693.12 Muscle_Skeletal
Some analyses (e.g. Mendelian randomisation) require data for
variants which may or may not be significant eQTLs. Use
calculate_expression_quantitative_trait_loci()
with
purrr::map()
to retrieve data for multiple variants
variants_of_interest <- c("rs12119111", "rs6605071", "rs1053870")
variants_of_interest |>
set_names() |>
map(
\(x) calculate_expression_quantitative_trait_loci(
tissueSiteDetailId = "Liver",
gencodeId = "ENSG00000237973.1",
variantId = x
)
) |>
bind_rows(.id = "rsid") |>
# optionally, reformat output - first extract genomic coordinates and alleles
tidyr::separate(
col = "variantId",
into = c(
"chromosome",
"position",
"reference_allele",
"alternative_allele",
"genome_build"
),
sep = "_"
) |>
# ...then ascertain alternative_allele frequency
mutate(
alt_allele_count = (2 * homoAltCount) + hetCount,
total_allele_count = 2 * (homoAltCount + hetCount + homoRefCount),
alternative_allele_frequency = alt_allele_count / total_allele_count
) |>
select(
rsid,
beta = nes,
se = error,
pValue,
minor_allele_frequency = maf,
alternative_allele_frequency,
chromosome:genome_build,
tissueSiteDetailId
)
#> # A tibble: 3 × 12
#> rsid beta se pValue minor_allele_frequency alternative_allele_f…¹
#> <chr> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1 rs121191… 0.0270 0.0670 6.88e-1 0.365 0.635
#> 2 rs6605071 -0.601 0.166 3.88e-4 0.0409 0.959
#> 3 rs1053870 0.0247 0.0738 7.38e-1 0.214 0.214
#> # ℹ abbreviated name: ¹alternative_allele_frequency
#> # ℹ 6 more variables: chromosome <chr>, position <chr>, reference_allele <chr>,
#> # alternative_allele <chr>, genome_build <chr>, tissueSiteDetailId <chr>