Exome-wide association study to identify rare variants influencing COVID-19 outcomes : Results from the Host Genetics Initiative

Publisher Copyright: Copyright: © 2022 Butler-Laporte et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Host genetics is a key determinant of COVID-19 outcomes. Previously, the COVID-19 Host Genetics Initiative genome-wide association study used common variants to identify multiple loci associated with COVID-19 outcomes. However, variants with the largest impact on COVID-19 outcomes are expected to be rare in the population. Hence, studying rare variants may provide additional insights into disease susceptibility and pathogenesis, thereby informing therapeutics development. Here, we combined whole-exome and whole-genome sequencing from 21 cohorts across 12 countries and performed rare variant exome-wide burden analyses for COVID-19 outcomes. In an analysis of 5,085 severe disease cases and 571,737 controls, we observed that carrying a rare deleterious variant in the SARS-CoV-2 sensor toll-like receptor TLR7 (on chromosome X) was associated with a 5.3-fold increase in severe disease (95% CI: 2.75–10.05, p = 5.41x10-7). This association was consistent across sexes. These results further support TLR7 as a genetic determinant of severe disease and suggest that larger studies on rare variants influencing COVID-19 outcomes could provide additional insights.Peer reviewe

Resolving the Genomic Complexity of Pediatric Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer in the Nordic countries. Structural chromosomal rearrangements are a hallmark of ALL and represent key markers for diagnosis, risk stratification and prognosis. Nevertheless, a substantial proportion of ALL cases (~25%) lack known risk-stratifying markers and are commonly referred to as the B-other subgroup. Improved delineation of structural alterations within this subgroup could provide additional information for diagnosis, prognosis and treatment decisions. Therefore, the aim of this thesis was to decipher the genetic alterations in pediatric ALL, focusing on patients in the B-other subgroup that lack known risk-stratifying markers, and to gain further understanding of the prognostic relevance of aberrant chromosomal changes in ALL. This thesis comprises four studies. In study I we identified a novel and recurrent fusion gene (PAX5-ESRRB) in four B-other patients using a combination of RNA-sequencing and copy number analysis. These patients displayed a distinct gene expression and DNA-methylation pattern that differed from other subtypes of ALL. In study II we further explored the fusion gene landscape in ALL by applying RNA-sequencing to 134 patient samples assigned to different subtypes, including the B-other subgroup. We detected several novel and recurrent fusion gene families in approximately 80% of the B-other patients of which several were associated with distinct DNA methylation and gene expression profiles. Following on from study II, in study III we utilized subtype-specific DNA methylation patterns to design DNA methylation-based classifiers to screen for subtype membership in ~1100 ALL samples including a large group of B-other samples (25%). Re-classification of B-other samples into a new subtype using DNA methylation as the sole marker for subtype classification was validated by RNA-sequencing, which identified previously unknown fusion genes. In study IV, “linked-read” whole genome sequencing was applied to 13 ALL samples for in-depth analysis of chromosomal rearrangements. We detected all known pathogenic variants with this technique and also identified previously unknown structural aberrations at a resolution beyond that obtained by traditional karyotyping. Together, these studies provide novel insights into the structural variation present in ALL and their potential clinical relevance, which may contribute to improved treatment stratification and risk-evaluation of children diagnosed with ALL in the future

Resolving the Genomic Complexity of Pediatric Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer in the Nordic countries. Structural chromosomal rearrangements are a hallmark of ALL and represent key markers for diagnosis, risk stratification and prognosis. Nevertheless, a substantial proportion of ALL cases (~25%) lack known risk-stratifying markers and are commonly referred to as the B-other subgroup. Improved delineation of structural alterations within this subgroup could provide additional information for diagnosis, prognosis and treatment decisions. Therefore, the aim of this thesis was to decipher the genetic alterations in pediatric ALL, focusing on patients in the B-other subgroup that lack known risk-stratifying markers, and to gain further understanding of the prognostic relevance of aberrant chromosomal changes in ALL. This thesis comprises four studies. In study I we identified a novel and recurrent fusion gene (PAX5-ESRRB) in four B-other patients using a combination of RNA-sequencing and copy number analysis. These patients displayed a distinct gene expression and DNA-methylation pattern that differed from other subtypes of ALL. In study II we further explored the fusion gene landscape in ALL by applying RNA-sequencing to 134 patient samples assigned to different subtypes, including the B-other subgroup. We detected several novel and recurrent fusion gene families in approximately 80% of the B-other patients of which several were associated with distinct DNA methylation and gene expression profiles. Following on from study II, in study III we utilized subtype-specific DNA methylation patterns to design DNA methylation-based classifiers to screen for subtype membership in ~1100 ALL samples including a large group of B-other samples (25%). Re-classification of B-other samples into a new subtype using DNA methylation as the sole marker for subtype classification was validated by RNA-sequencing, which identified previously unknown fusion genes. In study IV, “linked-read” whole genome sequencing was applied to 13 ALL samples for in-depth analysis of chromosomal rearrangements. We detected all known pathogenic variants with this technique and also identified previously unknown structural aberrations at a resolution beyond that obtained by traditional karyotyping. Together, these studies provide novel insights into the structural variation present in ALL and their potential clinical relevance, which may contribute to improved treatment stratification and risk-evaluation of children diagnosed with ALL in the future

Comparison of EM-seq and PBAT methylome library methods for low-input DNA

DNA methylation is the most studied epigenetic mark involved in regulation of gene expression. For low input samples, a limited number of methods for quantifying DNA methylation genome-wide has been evaluated. Here, we compared a series of input DNA amounts (1-10ng) from two methylome library preparation protocols, enzymatic methyl-seq (EM-seq) and post-bisulfite adaptor tagging (PBAT) adapted from single-cell PBAT. EM-seq takes advantage of enzymatic activity while PBAT relies on conventional bisulfite conversion for detection of DNA methylation. We found that both methods accurately quantified DNA methylation genome-wide. They produced expected distribution patterns around genomic features, high C-T transition efficiency at non-CpG sites and high correlation between input amounts. However, EM-seq performed better in regard to library and sequencing quality, i.e. EM-seq produced larger insert sizes, higher alignment rates and higher library complexity with lower duplication rate compared to PBAT. Moreover, EM-seq demonstrated higher CpG coverage, better CpG site overlap and higher consistency between input series. In summary, our data suggests that EM-seq overall performed better than PBAT in whole-genome methylation quantification of low input samples

RAG1 co-expression signature identifies ETV6-RUNX1-like B-cell precursor acute lymphoblastic leukemia in children

B-cell precursor acute lymphoblastic leukemia (BCP-ALL) can be classified into subtypes according to the genetic aberrations they display. For instance, the translocation t(12;21)(p13;q22), representing the ETV6-RUNX1 fusion gene (ER), is present in a quarter of BCP-ALL cases. However, around 10% of the cases lack classifying chromosomal abnormalities (B-other). In pediatric ER BCP-ALL, rearrangement mediated by RAG (recombination-activating genes) has been proposed as the predominant driver of oncogenic rearrangement. Herein we analyzed almost 1600 pediatric BCP-ALL samples to determine which subtypes express RAG. We demonstrate that RAG1 mRNA levels are especially high in the ETV6-RUNX1 (ER) subtype and in a subset of B-other samples. We also define 31 genes that are co-expressed with RAG1 (RAG1-signature) in the ER subtype, a signature that also identifies this subset of B-other samples. Moreover, this subset also shares leukemia and pro-B gene expression signatures as well as high levels of the ETV6 target genes (BIRC7, WBP1L, CLIC5, ANGPTL2) with the ER subtype, indicating that these B-other cases are the recently identified ER-like subtype. We validated our results in a cohort where ER-like has been defined, which confirmed expression of the RAG1-signature in this recently described subtype. Taken together, our results demonstrate that the RAG1-signature identifies the ER-like subtype. As there are no definitive genetic markers to identify this novel subtype, the RAG1-signature represents a means to screen for this leukemia in children

Refined detection and phasing of structural aberrations in pediatric acute lymphoblastic leukemia by linked-read whole-genome sequencing

Structural chromosomal rearrangements that can lead to in-frame gene-fusions are a leading source of information for diagnosis, risk stratification, and prognosis in pediatric acute lymphoblastic leukemia (ALL). Traditional methods such as karyotyping and FISH struggle to accurately identify and phase such large-scale chromosomal aberrations in ALL genomes. We therefore evaluated linked-read WGS for detecting chromosomal rearrangements in primary samples of from 12 patients diagnosed with ALL. We assessed the effect of input DNA quality on phased haplotype block size and the detectability of copy number aberrations and structural variants in the ALL genomes. We found that biobanked DNA isolated by standard column-based extraction methods was sufficient to detect chromosomal rearrangements even at low 10x sequencing coverage. Linked-read WGS enabled precise, allele-specific, digital karyotyping at a base-pair resolution for a wide range of structural variants including complex rearrangements and aneuploidy assessment. With use of haplotype information from the linked-reads, we also identified previously unknown structural variants, such as a compound heterozygous deletion of ERG in a patient with the DUX4-IGH fusion gene. We conclude that linked-read WGS allows detection of important pathogenic variants in ALL genomes at a resolution beyond that of traditional karyotyping and FISH