Using gpmapr

library(gpmapr)

Introduction

The gpmapr package provides a set of functions to interact with the GPMap API.

Getting started

The first port of entry is the search_gpmap function. This function allows you to search for a trait, gene, or variant.

haemoglobin <- search_gpmap("haemoglobin")
knitr::kable(haemoglobin[, c("name", "sample_size", "num_coloc_groups", "call")])
name sample_size num_coloc_groups call
43431 Glycated haemoglobin levels 146806 93 trait(915)
43436 Haemoglobin concentration 563946 828 trait(920)
43438 Mean corpuscular haemoglobin concentration 491553 297 trait(922)
43447 Haemoglobin 408112 757 trait(931)
44152 Haemoglobin levels 445373 775 trait(1636)
44156 Haemoglobin A1c levels 437749 838 trait(1640)
44499 Mean corpuscular haemoglobin 572863 936 trait(1983)
45100 Haemoglobin concentration (UKB data field 30020) 396624 658 trait(2584)
45127 Glycated haemoglobin HbA1c levels (UKB data field 30750) 389889 721 trait(2611)
47275 Haemoglobin concentration 350474 497 trait(4759)
47277 Mean corpuscular haemoglobin 350472 628 trait(4761)
47278 Mean corpuscular haemoglobin concentration 350468 137 trait(4762)
52158 Mean corpuscular haemoglobin 430998 628 trait(4761)
52788 Mean corpuscular haemoglobin concentration 430998 137 trait(4762)
53046 Glycated haemoglobin HbA1c (30750) 430998 0 trait(42778)
53057 Haemoglobin concentration 430998 497 trait(4759)

You can see information about the different traits that match your search, how to subsequently get more information (under call), and metadata about the trait (under info).

Understanding info

  • Extractions: Each trait has a number of extractions, related to the number of finemapped ld regions that had a p-value < 1.5e-4.
  • Colocalisation Groups: The number of colocalisation groups associated with the trait / gene / variant.
  • Colocalising Traits: The number of traits that are colocalising with the trait / gene / variant.
  • Rare Result Groups: Each trait has a number of rare result groups, related to the number of groups of rare result groups that had a p-value < 1.5e-4.

You can also search for a gene (by ENSG ID or gene name) or variant (by CHR:BP or rsID).

knitr::kable(search_gpmap("SLC44A")[, c("name", "sample_size", "num_study_extractions", "num_coloc_groups", "call")])
name sample_size num_study_extractions num_coloc_groups call
1032 SLC44A1 (ENSG00000070214) NA 206 9 gene(‘SLC44A1’)
5825 SLC44A2 (ENSG00000129353) NA 226 14 gene(‘SLC44A2’)
7196 SLC44A5 (ENSG00000137968) NA 91 9 gene(‘SLC44A5’)
7921 SLC44A3 (ENSG00000143036) NA 361 17 gene(‘SLC44A3’)
17220 SLC44A4 (ENSG00000204385) NA 107 12 gene(‘SLC44A4’)
19708 SLC44A3-AS1 (ENSG00000224081) NA 179 12 gene(‘SLC44A3-AS1’)
knitr::kable(search_gpmap("22:37042914"))
type name type_id num_coloc_groups num_coloc_studies num_rare_results num_study_extractions call
original_variant 22:37042914 T/C 5521294 0 0 0 NA variant(5521294)

Variant search returns proxy variants

The variant search will return the original variant and any proxy variants that are in LD with the original variant, which also have colocalisation results. Each variant is marked as either original_variant or proxy_variant. In this example, the original variant has no colocalisation results, but the proxy variant does. The proxy variant is also marked as having a r^2 of 0.96

proxy_variants <- search_gpmap("rs17078078")
knitr::kable(proxy_variants)
type name type_id num_coloc_groups num_coloc_studies num_rare_results num_study_extractions call
original_variant 3:45579683 A/C 5758009 0 0 0 NA variant(5758009)

Diving in

You can get more information about a trait by subsequently calling the trait(), gene(), or variant() functions. This will provide you with the colocalisation results, rare disease results, and study extractions.

Each trait, gene, or variant call have optional parameters:

  • include_associations: Whether to include associations (BETA, SE, P) of the variants in which it’s colocalised in the output.
  • include_coloc_pairs: Whether to include coloc pairs in the output (which include h3 and h4), as opposed to just the coloc groups.
  • h4_threshold: The h4 threshold for coloc pairs.

Trait example

hemoglobin_trait <- trait(931)
names(hemoglobin_trait)
#> [1] "trait"             "coloc_groups"      "study_extractions"
nrow(hemoglobin_trait$coloc_groups)
#> [1] 27999
nrow(hemoglobin_trait$study_extractions)
#> [1] 1342

This returns a list of elements, which you can access by name. More detailed explanations of the below are described in the API documentation.

  • trait: A list containing metadata about the trait, including common and rare studies associated with the trait
  • coloc_groups: a dataframe containing information about which studies have coloc results for this trait.
  • study_extractions: a list of dataframes containing the study extractions for this trait.
  • rare_results: (if they exist) a list of dataframes containing the rare results for this trait
  • associations: (optional) a dataframe containing the associations for the variants in which the trait is colocalised
  • coloc_pairs: (optional) a dataframe containing all pairwise coloc results for this trait.

How study_extractions, coloc_groups, and rare_results relate

All three layers refer to study extractions (GWAS hits in finemapped LD regions), keyed by id in study_extractions and by study_extraction_id in coloc_groups and rare_results.

Think of study_extractions as the catalogue of extractions linked to the trait or gene in the map: each row is a study signal at a locus. Not every listed extraction necessarily has a full colocalisation story or a rare-disease result row.

  • coloc_groups holds extractions that sit inside a colocalisation group (shared coloc evidence with other studies/traits at that locus). If a study extraction appears here, it has coloc-structured results for that entity.
  • rare_results holds extractions that belong to a rare-result group (rare-disease-style finemapping in the API). The same biological signal can, in principle, be reflected in both rare and common coloc paths, so overlap between this set of extraction ids and those in coloc_groups is possible.
  • Neither table: Some extractions appear only under study_extractions. They are still tied to the trait or gene in the genotype–phenotype map (for example via locus tagging, proximity, or other association logic in the pipeline), but they do not currently carry a coloc-group row or a rare-result group row. Treat those as “present on the map at this locus” rather than “absent by mistake.”

The same idea applies when you call gene() (or other entity-specific endpoints): study_extractions is the wider catalogue, while coloc_groups and rare_results subdivide it where those analyses exist. The table below illustrates counts for the hemoglobin trait example (trait(931)).

extraction_ids <- function(x) {
  if (is.null(x) || !length(x)) {
    return(integer(0))
  }
  id_col <- if ("id" %in% names(x)) "id" else NULL
  if (!is.null(id_col)) {
    return(unique(stats::na.omit(x[[id_col]])))
  }
  unique(stats::na.omit(unlist(lapply(x, function(df) {
    if (!is.data.frame(df)) {
      return(NULL)
    }
    if ("id" %in% names(df)) {
      return(df[["id"]])
    }
    NULL
  }))))
}

cg_ids <- unique(stats::na.omit(hemoglobin_trait$coloc_groups$study_extraction_id))

rr <- hemoglobin_trait$rare_results
rr_ids <- if (is.null(rr) || !length(rr)) {
  integer(0)
} else {
  unique(stats::na.omit(unlist(lapply(rr, function(d) {
    if (!is.data.frame(d) || !"study_extraction_id" %in% names(d)) {
      return(NULL)
    }
    d[["study_extraction_id"]]
  }))))
}

se_ids <- extraction_ids(hemoglobin_trait$study_extractions)

only_study_extractions <- setdiff(se_ids, union(cg_ids, rr_ids))

knitr::kable(data.frame(
  source = c(
    "Distinct study_extraction_id in coloc_groups",
    "Distinct study_extraction_id in rare_results",
    "In study_extractions only (not in coloc_groups nor rare_results)",
    "Total distinct extraction id in study_extractions"
  ),
  n_extractions = c(
    length(cg_ids),
    length(rr_ids),
    length(only_study_extractions),
    length(se_ids)
  )
))
source n_extractions
Distinct study_extraction_id in coloc_groups 27999
Distinct study_extraction_id in rare_results 0
In study_extractions only (not in coloc_groups nor rare_results) 585
Total distinct extraction id in study_extractions 1342

Gene example

slc44a1 <- gene("SLC44A1")
names(slc44a1)
#> [1] "gene"              "coloc_groups"      "rare_results"     
#> [4] "variants"          "study_extractions"
nrow(slc44a1$coloc_groups)
#> [1] 80
knitr::kable(head(slc44a1$coloc_groups[, c("coloc_group_id", "trait_name", "data_type", "tissue")]))
coloc_group_id trait_name data_type tissue
94136 SLC44A1 Skin Sun Exposed Lower leg sQTL chr9:105385502:105389033 Splice Variant Skin Sun Exposed Lower leg
94144 Treatment/medication code: alfuzosin Phenotype NA
94123 Phospholipids to total lipids ratio in medium HDL Phenotype NA
94141 SLC44A1 Brain (Meta) eQTL Gene Expression Brain (Meta)
94144 SLC44A1 Artery Aorta eQTL Gene Expression Artery Aorta
94137 Diagnoses - secondary ICD10: K66.0 Peritoneal adhesions Phenotype NA

Note that by default, the gene endpoint includes trans genetic effects. You can turn this off with gene("SLC44A1", include_trans = FALSE), or filter coloc_groups after the fact (for example cis_trans == "cis" or a min_p cutoff).

After you subset rows, some coloc_group_id values may be left with only a single row. Those are no longer meaningful colocalisation groups, so drop them by keeping only groups with more than one row:

slc44a1_no_trans <- slc44a1
slc44a1_no_trans$coloc_groups <- dplyr::filter(
  slc44a1_no_trans$coloc_groups,
  cis_trans == "cis"
)
# or e.g. dplyr::filter(..., min_p <= 5e-8)

slc44a1_no_trans$coloc_groups <- slc44a1_no_trans$coloc_groups |>
  dplyr::group_by(coloc_group_id) |>
  dplyr::filter(dplyr::n() > 1L) |>
  dplyr::ungroup()

nrow(slc44a1_no_trans$coloc_groups)
#> [1] 26
knitr::kable(head(slc44a1_no_trans$coloc_groups[, c("coloc_group_id", "trait_name", "data_type", "tissue")]))
coloc_group_id trait_name data_type tissue
94136 SLC44A1 Skin Sun Exposed Lower leg sQTL chr9:105385502:105389033 Splice Variant Skin Sun Exposed Lower leg
94144 SLC44A1 Artery Aorta eQTL Gene Expression Artery Aorta
94116 ABCA1 Blood eQTL Gene Expression Blood
94136 SLC44A1 Skin Sun Exposed Lower leg sQTL chr9:105385502:105438281 Splice Variant Skin Sun Exposed Lower leg
94116 CT70 Testis eQTL Gene Expression Testis
94123 SLC44A1 Blood eQTL Gene Expression Blood

Coloc pairs example

Although coloc groups provide a helpful overview of the colocalisation results for a gene, you may want to look at the pairwise relationships between the studies. You can do this by setting include_coloc_pairs = TRUE in the call.

As there may be many coloc pairs, the results are not as fleshed out as the coloc groups. You may have to filter the results to get the information you need, or join with the study extractions to get the full picture.

slc44a1_coloc_pairs <- gene("SLC44A1", include_coloc_pairs = TRUE)
nrow(slc44a1_coloc_pairs$coloc_pairs)
#> [1] 1096
knitr::kable(head(slc44a1_coloc_pairs$coloc_pairs[, c("study_extraction_a_id", "study_extraction_b_id", "h4")]))
study_extraction_a_id study_extraction_b_id h4
2469380 2469454 0.9971425
2469380 2469455 0.9969158
2469454 2469455 0.9999984
2469454 2469769 0.9071751
2469454 2469816 0.8388802
2469454 2469956 0.9998948

study_extractions_tbl <- dplyr::bind_rows(slc44a1_no_trans$study_extractions)
study_extractions_subset <- dplyr::select(study_extractions_tbl, id, trait_name, min_p)

hydrated_coloc_pairs <- slc44a1_coloc_pairs$coloc_pairs |>
  dplyr::left_join(slc44a1_coloc_pairs$study_extractions, by = c("study_extraction_a_id" = "id")) |>
  dplyr::rename(trait_a = trait_name) |>
  dplyr::left_join(slc44a1_coloc_pairs$study_extractions, by = c("study_extraction_b_id" = "id")) |>
  dplyr::rename(trait_b = trait_name)

knitr::kable(head(hydrated_coloc_pairs[, c("trait_a", "trait_b", "h4")]))
trait_a trait_b h4
HDL cholesterol Apolipoprotein A1 levels 0.9971425
HDL cholesterol HDL cholesterol levels 0.9969158
Apolipoprotein A1 levels HDL cholesterol levels 0.9999984
Apolipoprotein A1 levels Phospholipids to total lipids ratio in large HDL 0.9071751
Apolipoprotein A1 levels Phospholipids to total lipids ratio in medium HDL 0.8388802
Apolipoprotein A1 levels SLC44A1 Blood eQTL 0.9998948

Target–indication prioritisation workflow: Alzheimer’s disease

This section demonstrates a systematic workflow for using the GPMap to prioritise gene targets for a disease of interest. We use Alzheimer’s disease (AD) as an example.

The logic proceeds through four steps: 1. Get a list of genes mapped to AD via colocalisation. 2. Rank genes by pleiotropy score — low-pleiotropy genes are more specific to the indication. 3. Assess variant-level specificity — if a variant associates with many cis-genes, it provides weaker evidence for any single target. 4. Check consistency across multiple variants and rare results — concordant signals from independent loci and rare variant evidence strengthen the target–indication link.

Step 1: Genes mapped to Alzheimer’s disease

We start by searching for Alzheimer’s traits and then pulling their colocalisation groups to identify the set of genes that have colocalisation evidence with AD.

ad_search <- search_gpmap("alzheimer")
ad_trait_ids <- ad_search$type_id

ad_coloc <- dplyr::bind_rows(lapply(ad_trait_ids, function(tid) {
  tryCatch(trait(tid)$coloc_groups, error = function(e) NULL)
})) |>
  dplyr::filter(!grepl("methyl", .data$data_type, ignore.case = TRUE))

ad_genes <- ad_coloc |>
  dplyr::filter(!is.na(.data$gene_id)) |>
  dplyr::distinct(.data$gene_id, .data$gene)

nrow(ad_genes)
#> [1] 228

Step 2: Rank by gene-level pleiotropy

The GPMap provides a pre-computed pleiotropy score for every gene: distinct_trait_categories counts how many different phenotypic categories a gene’s coloc groups span. A low value means the gene’s associations are concentrated in a narrow phenotypic space — desirable for a drug target because it predicts fewer off-target effects.

We can retrieve pleiotropy scores for all genes at once using get_all_gene_pleiotropies() and join them to our AD gene list.

all_pleiotropy <- get_all_gene_pleiotropies()

ad_genes_ranked <- ad_genes |>
  dplyr::inner_join(
    all_pleiotropy[, c("gene_id", "distinct_trait_categories", "distinct_protein_coding_genes")],
    by = "gene_id"
  ) |>
  dplyr::arrange(.data$distinct_trait_categories)

There are a total of 176 genes mapped to Alzheimer’s disease. We can see some of the genes that are mapped to AD, and the number of colocalisation groups that each gene has.

Genes at the top of this list — those with very few distinct trait categories — are the most “specific” to Alzheimer’s disease. A gene appearing in many trait categories (high pleiotropy) is more likely to produce on-target side effects if therapeutically modulated.

Step 3: Variant-level specificity and consistency across variants and rare results

Each colocalisation group is anchored to a variant (an LD block). Within a single coloc group, the same variant may map to expression or protein QTLs of multiple cis-genes. When a variant associates with many cis-genes or trait categories, it provides weaker evidence that the gene would be a good drug target without potential off-target effects.

The strongest evidence for a target-indication pair comes when multiple independent variants (different LD blocks) and rare variant results all point to the same gene. This replication across loci greatly reduces the chance that any single colocalisation is spurious.

Let’s pick some of the top-ranked genes from Step 2 and check how many independent coloc groups and rare result groups support them.

top_genes <- head(ad_genes_ranked, 40)

gene_evidence <- lapply(top_genes$gene, function(g) {
  gi <- tryCatch(gene(g, include_associations = TRUE), error = function(e) NULL)
  if (is.null(gi)) return(NULL)

  cg <- gi$coloc_groups
  rr <- gi$rare_results

  ad_cg <- if (!is.null(cg) && nrow(cg) > 0) {
    cg[cg$trait_id %in% ad_trait_ids, ]
  } else {
    data.frame()
  }

  ad_rr <- if (!is.null(rr) && nrow(rr) > 0) {
    rr[rr$trait_id %in% ad_trait_ids, ]
  } else {
    data.frame()
  }

  n_tissues <- if (!is.null(cg) && nrow(cg) > 0 && "tissue" %in% names(cg)) {
    dplyr::n_distinct(cg$tissue[!is.na(cg$tissue)])
  } else {
    0L
  }

  data.frame(
    gene = g,
    n_coloc_groups = dplyr::n_distinct(ad_cg$coloc_group_id),
    n_tissues = n_tissues,
    n_rare_groups = if (nrow(ad_rr) > 0) dplyr::n_distinct(ad_rr$rare_result_group_id) else 0L
  )
}) |> dplyr::bind_rows()

ad_summary <- ad_genes_ranked |>
  dplyr::filter(.data$gene %in% gene_evidence$gene) |>
  dplyr::left_join(gene_evidence, by = "gene") |>
  dplyr::select("gene", "distinct_trait_categories", "distinct_protein_coding_genes",
                "n_tissues", "n_coloc_groups", "n_rare_groups") |>
  dplyr::arrange(.data$distinct_trait_categories, .data$gene)

ad_summary_long <- ad_summary |>
  tidyr::pivot_longer(
    cols = c("distinct_trait_categories", "distinct_protein_coding_genes",
             "n_tissues", "n_coloc_groups", "n_rare_groups"),
    names_to = "metric",
    values_to = "value"
  ) |>
  dplyr::mutate(
    metric = factor(.data$metric,
      levels = c("distinct_trait_categories", "distinct_protein_coding_genes",
                 "n_tissues", "n_coloc_groups", "n_rare_groups"),
      labels = c("Trait categories", "Protein-coding genes",
                 "Distinct tissues", "Colocalization groups", "Rare result groups")
    ),
    gene = factor(.data$gene, levels = rev(ad_summary$gene))
  )
ad_summary_plot <- ggplot2::ggplot(ad_summary_long, ggplot2::aes(x = value, y = gene, fill = metric)) +
  ggplot2::geom_col(show.legend = FALSE, width = 0.5) +
  ggplot2::facet_wrap(~ metric, scales = "free_x", nrow = 1) +
  ggplot2::labs(x = NULL, y = NULL, title = "Alzheimer's disease gene targets: pleiotropy and evidence summary") +
  ggplot2::theme_bw(base_size = 9) +
  ggplot2::theme(
    strip.text = ggplot2::element_text(face = "bold"),
    panel.grid.minor = ggplot2::element_blank(),
    panel.grid.major.y = ggplot2::element_blank(),
    axis.text.y = ggplot2::element_text(size = 5)
  )

ad_summary_plot

Genes with multiple coloc groups and supporting rare result groups have the most robust genetic evidence linking them to Alzheimer’s disease. Combined with low pleiotropy (few trait categories), these represent the highest-priority targets for further investigation.

Diving deeper: TREM2

From the table above, TREM2 stands out as a particularly interesting target for Alzheimer’s disease. It has very low pleiotropy (few trait categories), meaning its genetic associations are highly specific to AD rather than spread across many unrelated phenotypes. At the same time, it is supported by multiple coloc groups and rare result groups — independent lines of genetic evidence converging on the same gene.

Let’s examine TREM2 in more detail by looking at the direction of effect across all its AD-related colocalisation and rare variant signals.

trem2 <- gene("TREM2", include_associations = TRUE)
trem2$gene$distinct_trait_categories
#> [1] 1
trem2$gene$distinct_protein_coding_genes
#> [1] 2
trem2_ad_coloc_group_ids <- unique(
  trem2$coloc_groups[trem2$coloc_groups$trait_id %in% ad_trait_ids, ]$coloc_group_id
)
trem2_ad_rare_group_ids <- if (!is.null(trem2$rare_results) && nrow(trem2$rare_results) > 0) {
  unique(trem2$rare_results[trem2$rare_results$trait_id %in% ad_trait_ids, ]$rare_result_group_id)
} else {
  character(0)
}

trem2_ad_groups <- trem2$coloc_groups[
  trem2$coloc_groups$coloc_group_id %in% trem2_ad_coloc_group_ids,
]
trem2_ad_rare <- if (length(trem2_ad_rare_group_ids) == 0L) {
  trem2$rare_results[0, ]
} else {
  trem2$rare_results[
    trem2$rare_results$rare_result_group_id %in% trem2_ad_rare_group_ids,
  ]
}

The forest plot below shows the effect sizes (beta with 95% CI) for all colocalisation and rare result entries related to Alzheimer’s disease at TREM2. Panels are labelled with the variant and its MAF (minor allele frequency), and colour distinguishes molecular phenotypes (eQTL, pQTL, sQTL, etc.) from traits (disease GWAS).

trem2_all_rows <- dplyr::bind_rows(
  trem2_ad_groups,
  if (!is.null(trem2_ad_rare) && nrow(trem2_ad_rare) > 0L) trem2_ad_rare else NULL
)

variant_maf <- trem2_all_rows |>
  dplyr::filter(!is.na(.data$eaf)) |>
  dplyr::mutate(maf = pmin(.data$eaf, 1 - .data$eaf)) |>
  dplyr::group_by(.data$variant_id) |>
  dplyr::summarise(maf = min(.data$maf, na.rm = TRUE), .groups = "drop")

make_panel_label <- function(display_snp, variant_id, maf_lookup) {
  snp <- dplyr::coalesce(as.character(display_snp), paste0("variant ", as.character(variant_id)))
  maf <- maf_lookup$maf[match(variant_id, maf_lookup$variant_id)]
  maf_str <- ifelse(is.na(maf), "", paste0(" (MAF=", formatC(maf, format = "f", digits = 3), ")"))
  paste0(snp, maf_str)
}

trem2_forest_coloc <- trem2_ad_groups |>
  dplyr::filter(!is.na(.data$beta), !is.na(.data$se), .data$se > 0) |>
  dplyr::mutate(
    lo = .data$beta - 1.96 * .data$se,
    hi = .data$beta + 1.96 * .data$se,
    row_label = forest_row_label(.data$trait_name, .data$data_type, .data$tissue),
    panel_id = make_panel_label(.data$display_snp, .data$variant_id, variant_maf),
    data_type_label = label_data_type(.data$data_type)
  ) |>
  dplyr::group_by(.data$coloc_group_id) |>
  dplyr::arrange(.data$beta, .by_group = TRUE) |>
  dplyr::mutate(row_label = factor(.data$row_label, levels = unique(.data$row_label))) |>
  dplyr::ungroup()

trem2_forest_rare <- if (is.null(trem2_ad_rare) || nrow(trem2_ad_rare) == 0L) {
  NULL
} else {
  rr <- trem2_ad_rare
  if (!"tissue" %in% names(rr)) rr$tissue <- NA_character_
  if (!"eaf" %in% names(rr)) rr$eaf <- NA_real_
  rr |>
    dplyr::filter(!is.na(.data$beta), !is.na(.data$se), .data$se > 0) |>
    dplyr::mutate(
      lo = .data$beta - 1.96 * .data$se,
      hi = .data$beta + 1.96 * .data$se,
      row_label = forest_row_label(.data$trait_name, .data$data_type, .data$tissue),
      panel_id = make_panel_label(.data$display_snp, .data$variant_id, variant_maf),
      data_type_label = label_data_type(.data$data_type)
    ) |>
    dplyr::group_by(.data$panel_id) |>
    dplyr::arrange(.data$beta, .by_group = TRUE) |>
    dplyr::mutate(row_label = factor(.data$row_label, levels = unique(.data$row_label))) |>
    dplyr::ungroup()
}

trem2_forest <- dplyr::bind_rows(trem2_forest_coloc, trem2_forest_rare) |>
  dplyr::mutate(panel_id = factor(.data$panel_id, levels = unique(.data$panel_id)))

cbf_palette <- c(
  "Gene Expression" = "#0072B2",
  "Splice Variant"  = "#E69F00",
  "Protein"         = "#009E73",
  "Plasma Protein"  = "#56B4E9",
  "Transcript"      = "#CC79A7",
  "Methylation"     = "#F0E442",
  "Metabolome"      = "#D55E00",
  "Cell Trait"      = "#999999",
  "Phenotype"       = "#000000"
)

ggplot2::ggplot(trem2_forest, ggplot2::aes(x = beta, y = row_label, colour = data_type_label)) +
  ggplot2::geom_vline(xintercept = 0, linetype = 2, colour = "grey55") +
  ggplot2::geom_errorbarh(
    ggplot2::aes(xmin = lo, xmax = hi), height = 0, linewidth = 0.35
  ) +
  ggplot2::geom_point(size = 2) +
  ggplot2::facet_wrap(~ panel_id, scales = "free_y", ncol = 1) +
  ggplot2::scale_colour_manual(values = cbf_palette) +
  ggplot2::labs(
    x = "Effect (beta) with 95% CI", y = NULL,
    colour = "Data type", title = "TREM2 \u2014 Alzheimer's disease"
  ) +
  ggplot2::theme_bw() +
  ggplot2::theme(
    strip.text = ggplot2::element_text(face = "bold"),
    panel.grid.minor = ggplot2::element_blank(),
    legend.position = "bottom",
    legend.direction = "vertical"
  ) +
  ggplot2::guides(colour = ggplot2::guide_legend(ncol = 1))
#> Warning: `geom_errorbarh()` was deprecated in ggplot2 4.0.0.
#> ℹ Please use the `orientation` argument of `geom_errorbar()` instead.
#> This warning is displayed once per session.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
#> generated.
#> `height` was translated to `width`.

TREM2 shows colocalisation evidence from multiple independent variants, supported by rare result groups. The direction of effect appears complex — in some instances increased TREM2 expression associates with increased AD risk, while in others the direction is reversed — reflecting the biological complexity of TREM2 signalling in neuroinflammation. Nonetheless, the convergence of evidence from multiple loci and data types makes it a compelling target, and it is indeed currently under active investigation as a therapeutic target for Alzheimer’s disease.

Putting it together

This four-step workflow uses the GPMap to move from a broad disease search to a prioritised shortlist of gene targets:

Step Question GPMap function
1 Which genes colocalise with my disease? search_gpmap()trait()
2 Which are most specific (least pleiotropic)? get_all_gene_pleiotropies()
3 Do variants map cleanly to one cis-gene? coloc_groups$gene_id per coloc_group_id
4 Is the evidence replicated across loci? gene() → count coloc groups, variants, rare results

A gene that scores well on all four criteria — colocalises with AD, has low pleiotropy, is supported by high-specificity variants, and is replicated across multiple loci including rare variants — is a strong candidate for target validation and drug development.

Accessing summary statistics

You can only access the summary statistics via variant(), by including include_summary_stats = TRUE in the call. This is to limit the amount of data that can be returned from the API for cost reasons. If you attempt to download too many summary statistics, you may be blocked from the API.

  • variant(1669064, include_summary_stats = TRUE)

Instead, if you are interested in accessing all the summary statistics, or the whole database of results, you can download all databases and summary statistics the Google Cloud Storage Bucket, and can find an explanation of the files here. Note that the bucket is ‘requester pays’, so you will need to have a Google Cloud account and be logged in to download the files.