Evaluation of Hi-C sequencing for the detection of gene fusions in hematologic and solid pediatric cancer samples.

HiC sequencing is a DNA-based next-generation sequencing method that preserves the 3D conformation of the genome and has shown promise in detecting genomic rearrangements in translational research studies. To evaluate HiC as a potential clinical diagnostic platform, analytical concordance with routine laboratory testing was assessed using primary pediatric leukemia and sarcoma specimens previously positive for clinically significant genomic rearrangements. Archived specimen types tested included viable and nonviable frozen leukemic cells, as well as formalin-fixed paraffin-embedded (FFPE) tumor tissues. Initially, pediatric acute myeloid leukemia (AML) and alveolar rhabdomyosarcoma (A-RMS) specimens with known genomic rearrangements were subjected to HiC analysis to assess analytical concordance. Subsequently, a discovery cohort consisting of AML and acute lymphoblastic leukemia (ALL) cases with no known genomic rearrangements based on prior clinical diagnostic testing were evaluated to determine whether HiC could detect rearrangements. Using a standard sequencing depth of 50 million raw read-pairs per sample, or approximately 5X raw genomic coverage, 100% concordance was observed between HiC and previous clinical cytogenetic and molecular testing. In the discovery cohort, a clinically relevant gene fusion was detected in 45% of leukemia cases (5/11). This study demonstrates the value of HiC sequencing to medical diagnostic testing as it identified several clinically significant rearrangements, including those that might have been missed by current clinical testing workflows. Key points: HiC sequencing is a DNA-based next-generation sequencing method that preserves the 3D conformation of the genome, facilitating detection of genomic rearrangements.HiC was 100% concordant with clinical diagnostic testing workflows for detecting clinically significant genomic rearrangements in pediatric leukemia and rhabdomyosarcoma specimens.HiC detected clinically significant genomic rearrangements not previously detected by prior clinical cytogenetic and molecular testing.HiC performed well with archived non-viable and viable frozen leukemic cell samples, as well as archived formalin-fixed paraffin-embedded tumor tissue specimens.

Severus: accurate detection and characterization of somatic structural variation in tumor genomes using long reads.

Most current studies rely on short-read sequencing to detect somatic structural variation (SV) in cancer genomes. Long-read sequencing offers the advantage of better mappability and long-range phasing, which results in substantial improvements in germline SV detection. However, current long-read SV detection methods do not generalize well to the analysis of somatic SVs in tumor genomes with complex rearrangements, heterogeneity, and aneuploidy. Here, we present Severus: a method for the accurate detection of different types of somatic SVs using a phased breakpoint graph approach. To benchmark various short- and long-read SV detection methods, we sequenced five tumor/normal cell line pairs with Illumina, Nanopore, and PacBio sequencing platforms; on this benchmark Severus showed the highest F1 scores (harmonic mean of the precision and recall) as compared to long-read and short-read methods. We then applied Severus to three clinical cases of pediatric cancer, demonstrating concordance with known genetic findings as well as revealing clinically relevant cryptic rearrangements missed by standard genomic panels.

POLR1A variants underlie phenotypic heterogeneity in craniofacial, neural, and cardiac anomalies.

Heterozygous pathogenic variants in POLR1A, which encodes the largest subunit of RNA Polymerase I, were previously identified as the cause of acrofacial dysostosis, Cincinnati-type. The predominant phenotypes observed in the cohort of 3 individuals were craniofacial anomalies reminiscent of Treacher Collins syndrome. We subsequently identified 17 additional individuals with 12 unique heterozygous variants in POLR1A and observed numerous additional phenotypes including neurodevelopmental abnormalities and structural cardiac defects, in combination with highly prevalent craniofacial anomalies and variable limb defects. To understand the pathogenesis of this pleiotropy, we modeled an allelic series of POLR1A variants in vitro and in vivo. In vitro assessments demonstrate variable effects of individual pathogenic variants on ribosomal RNA synthesis and nucleolar morphology, which supports the possibility of variant-specific phenotypic effects in affected individuals. To further explore variant-specific effects in vivo, we used CRISPR-Cas9 gene editing to recapitulate two human variants in mice. Additionally, spatiotemporal requirements for Polr1a in developmental lineages contributing to congenital anomalies in affected individuals were examined via conditional mutagenesis in neural crest cells (face and heart), the second heart field (cardiac outflow tract and right ventricle), and forebrain precursors in mice. Consistent with its ubiquitous role in the essential function of ribosome biogenesis, we observed that loss of Polr1a in any of these lineages causes cell-autonomous apoptosis resulting in embryonic malformations. Altogether, our work greatly expands the phenotype of human POLR1A-related disorders and demonstrates variant-specific effects that provide insights into the underlying pathogenesis of ribosomopathies.

Integrated genetic profiling of archival pediatric high-grade glial tumors and reassessment with 2021 WHO classification of paediatric CNS tumours.

Though rare, pediatric high-grade gliomas (pHGG) are a leading cause of cancer-related mortality in children. We wanted to determine whether our currently available clinical laboratory methods could better define diagnosis for pHGG that had been archived at our institution for the past 20 years (1998 to 2017). We investigated 33 formalin-fixed paraffin-embedded pHGG using ThermoFisher Oncoscan SNP microarray with somatic mutation analysis, Sanger sequencing, and whole genome sequencing. These data were correlated with historical histopathological, chromosomal, clinical, and radiological data. Tumors were subsequently classified according to the 2021 WHO Classification of Paediatric CNS Tumours. All 33 tumors were found to have genetic aberrations that placed them within a 2021 WHO subtype and/or provided prognostic information; 6 tumors were upgraded from WHO CNS grade 3 to grade 4. New pHGG genetic features were found including two small cell glioblastomas with H3 G34 mutations not previously described; one tumor with STRN-NTRK2 fusion; and a congenital diffuse leptomeningeal glioneuronal tumor without a chromosomal 1p deletion but with KIAA1549-BRAF fusion. Overall, the combination of laboratory methods yielded key information for tumor classification. Thus, even small studies of these uncommon tumor types may yield new genetic features and possible new subtypes that warrant future investigations.

Genome-wide analysis of copy-number variation in humans with cleft lip and/or cleft palate identifies COBLL1, RIC1, and ARHGEF38 as clefting genes.

Cleft lip with or without cleft palate (CL/P) is a common birth defect with a complex, heterogeneous etiology. It is well established that common and rare sequence variants contribute to the formation of CL/P, but the contribution of copy-number variants (CNVs) to cleft formation remains relatively understudied. To fill this knowledge gap, we conducted a large-scale comparative analysis of genome-wide CNV profiles of 869 individuals from the Philippines and 233 individuals of European ancestry with CL/P with three primary goals: first, to evaluate whether differences in CNV number, amount of genomic content, or amount of coding genomic content existed within clefting subtypes; second, to assess whether CNVs in our cohort overlapped with known Mendelian clefting loci; and third, to identify unestablished Mendelian clefting genes. Significant differences in CNVs across cleft types or in individuals with non-syndromic versus syndromic clefts were not observed; however, several CNVs in our cohort overlapped with known syndromic and non-syndromic Mendelian clefting loci. Moreover, employing a filtering strategy relying on population genetics data that rare variants are on the whole more deleterious than common variants, we identify several CNV-associated gene losses likely driving non-syndromic clefting phenotypes. By prioritizing genes deleted at a rare frequency across multiple individuals with clefts yet enriched in our cohort of individuals with clefts compared to control subjects, we identify COBLL1, RIC1, and ARHGEF38 as clefting genes. CRISPR-Cas9 mutagenesis of these genes in Xenopus laevis and Danio rerio yielded craniofacial dysmorphologies, including clefts analogous to those seen in human clefting disorders.

Clinical Validation of Genome Reference Consortium Human Build 38 in a Laboratory Utilizing Next-Generation Sequencing Technologies.

BACKGROUND: Laboratories utilizing next-generation sequencing align sequence data to a standardized human reference genome (HRG). Several updated versions, or builds, have been released since the original HRG in 2001, including the Genome Reference Consortium Human Build 38 (GRCh38) in 2013. However, most clinical laboratories still use GRCh37, which was released in 2009. We report our laboratory's clinical validation of GRCh38. METHODS: Migration to GRCh38 was validated by comparing the coordinates (lifting over) of 9443 internally curated variants from GRCh37 to GRCh38, globally comparing protein coding sequence variants aligned with GRCh37 vs GRCh38 from 917 exomes, assessing genes with known discrepancies, comparing coverage differences, and establishing the analytic sensitivity and specificity of variant detection using Genome in a Bottle data. RESULTS: Eight discrepancies, due to strand swap or reference base, were observed. Three clinically relevant variants had the GRCh37 alternate allele as the reference allele in GRCh38. A comparison of 88 295 calls between builds identified 8 disease-associated genes with sequence differences: ABO, BNC2, KIZ, NEFL, NR2E3, PTPRQ, SHANK2, and SRD5A2. Discrepancies in coding regions in GRCh37 were resolved in GRCh38. CONCLUSIONS: There were a small number of clinically significant changes between the 2 genome builds. GRCh38 provided improved detection of nucleotide changes due to the resolution of discrepancies present in GRCh37. Implementation of GRCh38 results in more accurate and consistent reporting.

A novel likely pathogenic variant in a patient with Hermansky-Pudlak syndrome.

Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by oculocutaneous albinism and variable pulmonary fibrosis, granulomatous colitis, or immunodeficiency. The diagnosis relies on clinical findings, platelet transmission electron microscopy studies showing absent dense granules, or the identification of a pathogenic genotype in one of 11 associated genes, including HPS1 We report a 2-wk-old male with significant iris transillumination defects, a pale fundus, and mild corectopia found by clinical exome sequencing to have a previously reported pathogenic variant, c.972dupC p.(Met325HisfsTer128), and a variant of uncertain significance, c.1846G>A p.(Glu616Lys), in HPS1 To determine whether his phenotype was consistent with HPS, follow-up studies of whole blood lumiaggregometry and platelet transmission electron microscopy were performed that revealed absent or markedly reduced platelet ATP secretion and virtually absent platelet dense granules, thus confirming the diagnosis. To the best of our knowledge, our case is the first in which the c.1846G>A p.(Glu616Lys) variant is identified in a patient with HPS. In addition, the case also highlights the importance of leveraging appropriate confirmatory clinical testing and reverse phenotyping, which allowed the care team to establish the clinical diagnosis of HPS and reclassify the previously reported variant of uncertain significance in HPS1 to likely pathogenic.

Second patient with GNB2-related neurodevelopmental disease: Further evidence for a gene-disease association.

G-proteins are ubiquitously expressed heterotrimeric proteins consisting of α, ß and γ subunits and mediate G-protein coupled receptor signalling cascades. The ß subunit is encoded by one of five highly similar paralogs (GNB1-GNB5, accordingly). The developmental importance of G-proteins is highlighted by the clinical relevance of variants in genes such as GNB1, which cause severe neurodevelopmental disease (NDD). Recently the candidacy of GNB2 was raised in association with NDD in an individual with a de novo variant affecting a codon conserved across paralogs and recurrently mutated in GNB1-related disease, c.229G>A p.(Gly77Arg), in association with global developmental delay, intellectual disability and dysmorphic features. Here, we report a patient with strikingly similar facial features and NDD in association with a de novo GNB2 variant affecting the same codon, c.229G>T p.(Gly77Trp). In addition, this individual has epilepsy and overgrowth. Our report is the second to implicate a de novo GNB2 variant with a severe yet variable NDD.

Factors Affecting Migration to GRCh38 in Laboratories Performing Clinical Next-Generation Sequencing.

The most recent build of the human reference genome, GRCh38, was released in 2013. However, many laboratories performing next-generation sequencing (NGS) continue to align to GRCh37. Our aim was to assess the number of clinical diagnostic laboratories that have migrated to GRCh38 and discern factors impeding migration for those still using GRCh37. A brief, five-question survey was electronically administered to 71 clinical laboratories offering constitutional NGS-based testing and analyzed categorically. Twenty-eight responses meeting inclusion criteria were collected from 24 academic and four commercial diagnostic laboratories. Most of these (14; 50%) reported volumes of <500 NGS-based tests in 2019. Only two respondents (7%) had already migrated entirely to GRCh38; most laboratories (15; 54%) had no plans to migrate. The two prevailing reasons for not yet migrating were as follows: laboratories did not feel the benefits outweighed the time and monetary costs (14; 50%); and laboratories had insufficient staff to facilitate the migration (12; 43%). These data, although limited, suggest most clinical molecular laboratories are reluctant to migrate to GRCh38, and there appear to be multiple obstacles to overcome before GRCh38 is widely adopted.

Using an aquatic model, Xenopus laevis, to uncover the role of chromodomain 1 in craniofacial disorders.

The chromodomain family member chromodomain 1 (CHD1) has been shown to have numerous critical molecular functions including transcriptional regulation, splicing, and DNA repair. Complete loss of function of this gene is not compatible with life. On the other hand, missense and copy number variants of CHD1 can result in intellectual disabilities and craniofacial malformations in human patients including cleft palate and Pilarowski-Bjornsson Syndrome. We have used the aquatic developmental model organism Xenopus laevis, to determine a specific role for Chd1 in such cranioafcial disorders. Protein and gene knockdown techniques in Xenopus, including antisense oligos and mosaic Crispr/Cas9-mediated mutagenesis, recapitulated the craniofacial defects observed in humans. Further analysis indicated that embryos deficient in Chd1 had defects in cranial neural crest development and jaw cartilage morphology. Additionally, flow cytometry and immunohistochemistry revealed that decreased Chd1 resulted in increased in apoptosis in the developing head. Together, these experiments demonstrate that Chd1 is critical for fundamental processes and cell survival in craniofacial development. We also presented evidence that Chd1 is regulated by retinoic acid signaling during craniofacial development. Expression levels of chd1 mRNA, specifically in the head, were increased by RAR agonist exposure and decreased upon antagonist treatment. Subphenotypic levels of an RAR antagonist and Chd1 morpholinos synergized to result in orofacial defects. Further, RAR DNA binding sequences (RAREs) were detected in chd1 regulatory regions by bioinformatic analysis. In summary, by combining human genetics and experiments in an aquatic model we now have a better understanding of the role of CHD1 in craniofacial disorders.

Identification of Isthmin 1 as a Novel Clefting and Craniofacial Patterning Gene in Humans.

Orofacial clefts are one of the most common birth defects, affecting 1-2 per 1000 births, and have a complex etiology. High-resolution array-based comparative genomic hybridization has increased the ability to detect copy number variants (CNVs) that can be causative for complex diseases such as cleft lip and/or palate. Utilizing this technique on 97 nonsyndromic cleft lip and palate cases and 43 cases with cleft palate only, we identified a heterozygous deletion of Isthmin 1 in one affected case, as well as a deletion in a second case that removes putative 3' regulatory information. Isthmin 1 is a strong candidate for clefting, as it is expressed in orofacial structures derived from the first branchial arch and is also in the same "synexpression group" as fibroblast growth factor 8 and sprouty RTK signaling antagonist 1a and 2, all of which have been associated with clefting. CNVs affecting Isthmin 1 are exceedingly rare in control populations, and Isthmin 1 scores as a likely haploinsufficiency locus. Confirming its role in craniofacial development, knockdown or clustered randomly interspaced short palindromic repeats/Cas9-generated mutation of isthmin 1 in Xenopus laevis resulted in mild to severe craniofacial dysmorphologies, with several individuals presenting with median clefts. Moreover, knockdown of isthmin 1 produced decreased expression of LIM homeobox 8, itself a gene associated with clefting, in regions of the face that pattern the maxilla. Our study demonstrates a successful pipeline from CNV identification of a candidate gene to functional validation in a vertebrate model system, and reveals Isthmin 1 as both a new human clefting locus as well as a key craniofacial patterning gene.