Tracing Oncogene Rearrangements in the Mutational History of Lung Adenocarcinoma.

Mutational processes giving rise to lung adenocarcinomas (LADCs) in non-smokers remain elusive. We analyzed 138 LADC whole genomes, including 83 cases with minimal contribution of smoking-associated mutational signature. Genomic rearrangements were not correlated with smoking-associated mutations and frequently served as driver events of smoking-signature-low LADCs. Complex genomic rearrangements, including chromothripsis and chromoplexy, generated 74% of known fusion oncogenes, including EML4-ALK, CD74-ROS1, and KIF5B-RET. Unlike other collateral rearrangements, these fusion-oncogene-associated rearrangements were frequently copy-number-balanced, representing a genomic signature of early oncogenesis. Analysis of mutation timing revealed that fusions and point mutations of canonical oncogenes were often acquired in the early decades of life. During a long latency, cancer-related genes were disrupted or amplified by complex rearrangements. The genomic landscape was different between subgroups-EGFR-mutant LADCs had frequent whole-genome duplications with p53 mutations, whereas fusion-oncogene-driven LADCs had frequent SETD2 mutations. Our study highlights LADC oncogenesis driven by endogenous mutational processes.

Multi-step control of homologous recombination via Mec1/ATR suppresses chromosomal rearrangements.

The Mec1/ATR kinase is crucial for genome stability, yet the mechanism by which it prevents gross chromosomal rearrangements (GCRs) remains unknown. Here we find that in cells with deficient Mec1 signaling, GCRs accumulate due to the deregulation of multiple steps in homologous recombination (HR). Mec1 primarily suppresses GCRs through its role in activating the canonical checkpoint kinase Rad53, which ensures the proper control of DNA end resection. Upon loss of Rad53 signaling and resection control, Mec1 becomes hyperactivated and triggers a salvage pathway in which the Sgs1 helicase is recruited to sites of DNA lesions via the 911-Dpb11 scaffolds and phosphorylated by Mec1 to favor heteroduplex rejection and limit HR-driven GCR accumulation. Fusing an ssDNA recognition domain to Sgs1 bypasses the requirement of Mec1 signaling for GCR suppression and nearly eliminates D-loop formation, thus preventing non-allelic recombination events. We propose that Mec1 regulates multiple steps of HR to prevent GCRs while ensuring balanced HR usage when needed for promoting tolerance to replication stress.

The impact of inversions across 33,924 families with rare disease from a national genome sequencing project.

Detection of structural variants (SVs) is currently biased toward those that alter copy number. The relative contribution of inversions toward genetic disease is unclear. In this study, we analyzed genome sequencing data for 33,924 families with rare disease from the 100,000 Genomes Project. From a database hosting >500 million SVs, we focused on 351 genes where haploinsufficiency is a confirmed disease mechanism and identified 47 ultra-rare rearrangements that included an inversion (24 bp to 36.4 Mb, 20/47 de novo). Validation utilized a number of orthogonal approaches, including retrospective exome analysis. RNA-seq data supported the respective diagnoses for six participants. Phenotypic blending was apparent in four probands. Diagnostic odysseys were a common theme (>50 years for one individual), and targeted analysis for the specific gene had already been performed for 30% of these individuals but with no findings. We provide formal confirmation of a European founder origin for an intragenic MSH2 inversion. For two individuals with complex SVs involving the MECP2 mutational hotspot, ambiguous SV structures were resolved using long-read sequencing, influencing clinical interpretation. A de novo inversion of HOXD11-13 was uncovered in a family with Kantaputra-type mesomelic dysplasia. Lastly, a complex translocation disrupting APC and involving nine rearranged segments confirmed a clinical diagnosis for three family members and resolved a conundrum for a sibling with a single polyp. Overall, inversions play a small but notable role in rare disease, likely explaining the etiology in around 1/750 families across heterogeneous clinical cohorts.

Mitotic CDK Promotes Replisome Disassembly, Fork Breakage, and Complex DNA Rearrangements.

DNA replication errors generate complex chromosomal rearrangements and thereby contribute to tumorigenesis and other human diseases. One mechanism that triggers these errors is mitotic entry before the completion of DNA replication. To address how mitosis might affect DNA replication, we used Xenopus egg extracts. When mitotic CDK (Cyclin B1-CDK1) is used to drive interphase egg extracts into a mitotic state, the replicative CMG (CDC45/MCM2-7/GINS) helicase undergoes ubiquitylation on its MCM7 subunit, dependent on the E3 ubiquitin ligase TRAIP. Whether replisomes have stalled or undergone termination, CMG ubiquitylation is followed by its extraction from chromatin by the CDC48/p97 ATPase. TRAIP-dependent CMG unloading during mitosis is also seen in C. elegans early embryos. At stalled forks, CMG removal results in fork breakage and end joining events involving deletions and templated insertions. Our results identify a mitotic pathway of global replisome disassembly that can trigger replication fork collapse and DNA rearrangements.

A region of suppressed recombination misleads neoavian phylogenomics.

Genomes are typically mosaics of regions with different evolutionary histories. When speciation events are closely spaced in time, recombination makes the regions sharing the same history small, and the evolutionary history changes rapidly as we move along the genome. When examining rapid radiations such as the early diversification of Neoaves 66 Mya, typically no consistent history is observed across segments exceeding kilobases of the genome. Here, we report an exception. We found that a 21-Mb region in avian genomes, mapped to chicken chromosome 4, shows an extremely strong and discordance-free signal for a history different from that of the inferred species tree. Such a strong discordance-free signal, indicative of suppressed recombination across many millions of base pairs, is not observed elsewhere in the genome for any deep avian relationships. Although long regions with suppressed recombination have been documented in recently diverged species, our results pertain to relationships dating circa 65 Mya. We provide evidence that this strong signal may be due to an ancient rearrangement that blocked recombination and remained polymorphic for several million years prior to fixation. We show that the presence of this region has misled previous phylogenomic efforts with lower taxon sampling, showing the interplay between taxon and locus sampling. We predict that similar ancient rearrangements may confound phylogenetic analyses in other clades, pointing to a need for new analytical models that incorporate the possibility of such events.

Small RNA-mediated genome rearrangement pathways in ciliates.

Most eukaryotes employ a combination of transcriptional and post-transcriptional silencing mechanisms to suppress transposons, yet ciliates employ a more extreme approach. They separate germline and somatic functions into distinct nuclei, enabling the elimination of transposons from the active somatic genome through diverse small RNA-mediated genome rearrangement pathways during sexual processes.

The PAX5-JAK2 translocation acts as dual-hit mutation that promotes aggressive B-cell leukemia via nuclear STAT5 activation.

While PAX5 is an important tumor suppressor gene in B-cell acute lymphoblastic leukemia (B-ALL), it is also involved in oncogenic translocations coding for diverse PAX5 fusion proteins. PAX5-JAK2 encodes a protein consisting of the PAX5 DNA-binding region fused to the constitutively active JAK2 kinase domain. Here, we studied the oncogenic function of the PAX5-JAK2 fusion protein in a mouse model expressing it from the endogenous Pax5 locus, resulting in inactivation of one of the two Pax5 alleles. Pax5Jak2/+ mice rapidly developed an aggressive B-ALL in the absence of another cooperating exogenous gene mutation. The DNA-binding function and kinase activity of Pax5-Jak2 as well as IL-7 signaling contributed to leukemia development. Interestingly, all Pax5Jak2/+ tumors lost the remaining wild-type Pax5 allele, allowing efficient DNA-binding of Pax5-Jak2. While we could not find evidence for a nuclear role of Pax5-Jak2 as an epigenetic regulator, high levels of active phosphorylated STAT5 and increased expression of STAT5 target genes were seen in Pax5Jak2/+ B-ALL tumors, implying that nuclear Pax5-Jak2 phosphorylates STAT5. Together, these data reveal Pax5-Jak2 as an important nuclear driver of leukemogenesis by maintaining phosphorylated STAT5 levels in the nucleus.

TIAM-1 regulates polarized protrusions during dorsal intercalation in the Caenorhabditis elegans embryo through both its GEF and N-terminal domains.

Mediolateral cell intercalation is a morphogenetic strategy used throughout animal development to reshape tissues. Dorsal intercalation in the Caenorhabditis elegans embryo involves the mediolateral intercalation of two rows of dorsal epidermal cells to create a single row that straddles the dorsal midline, and thus is a simple model to study cell intercalation. Polarized protrusive activity during dorsal intercalation requires the C. elegans Rac and RhoG orthologs CED-10 and MIG-2, but how these GTPases are regulated during intercalation has not been thoroughly investigated. In this study, we characterized the role of the Rac-specific guanine nucleotide exchange factor (GEF) TIAM-1 in regulating actin-based protrusive dynamics during dorsal intercalation. We found that TIAM-1 can promote formation of the main medial lamellipodial protrusion extended by intercalating cells through its canonical GEF function, whereas its N-terminal domains function to negatively regulate the generation of ectopic filiform protrusions around the periphery of intercalating cells. We also show that the guidance receptor UNC-5 inhibits these ectopic filiform protrusions in dorsal epidermal cells and that this effect is in part mediated via TIAM-1. These results expand the network of proteins that regulate basolateral protrusive activity during directed rearrangement of epithelial cells in animal embryos.

Repeat-mediated deletions can be induced by a chromosomal break far from a repeat, but multiple pathways suppress such rearrangements.

Chromosomal deletion rearrangements mediated by repetitive elements often involve repeats separated by several kilobases and sequences that are divergent. While such rearrangements are likely induced by DNA double-strand breaks (DSBs), it has been unclear how the proximity of DSBs relative to repeat sequences affects the frequency of such events. We generated a reporter assay in mouse cells for a deletion rearrangement involving repeats separated by 0.4 Mb. We induced this repeat-mediated deletion (RMD) rearrangement with two DSBs: the 5' DSB that is just downstream from the first repeat and the 3' DSB that is varying distances upstream of the second repeat. Strikingly, we found that increasing the 3' DSB/repeat distance from 3.3 kb to 28.4 kb causes only a modest decrease in rearrangement frequency. We also found that RMDs are suppressed by KU70 and RAD51 and promoted by RAD52, CtIP, and BRCA1. In addition, we found that 1%-3% sequence divergence substantially suppresses these rearrangements in a manner dependent on the mismatch repair factor MSH2, which is dominant over the suppressive role of KU70. We suggest that a DSB far from a repeat can stimulate repeat-mediated rearrangements, but multiple pathways suppress these events.

Transforming mutations in the development of pathogenic B cell clones and autoantibodies.

Autoimmune diseases are characterized by serum autoantibodies, some of which are pathogenic, causing severe manifestations and organ injury. However, autoantibodies of the same antigenic reactivity are also present in the serum of asymptomatic people years before they develop any clinical signs of autoimmunity. Autoantibodies can arise during multiple stages of B cell development, and various genetic and environmental factors drive their production. However, what drives the development of pathogenic autoantibodies is poorly understood. Advances in single-cell technology have enabled the deep analysis of rare B cell clones producing pathogenic autoantibodies responsible for vasculitis in patients with primary Sjögren's syndrome complicated by mixed cryoglobulinaemia. These findings demonstrated a cascade of genetic events involving stereotypic immunoglobulin V(D)J recombination and transforming somatic mutations in lymphoma genes and V(D)J regions that disrupted antibody quality control mechanisms and decreased autoantibody solubility. Most studies consider V(D)J mutations that enhance autoantibody affinity to drive pathology; however, V(D)J mutations that increase autoantibody propensity to form insoluble complexes could be a major contributor to autoantibody pathogenicity. Defining the molecular characteristics of pathogenic autoantibodies and failed tolerance checkpoints driving their formation will improve prognostication, enabling early treatment to prevent escalating organ damage and B cell malignancy.

Annelid Comparative Genomics and the Evolution of Massive Lineage-Specific Genome Rearrangement in Bilaterians.

The organization of genomes into chromosomes is critical for processes such as genetic recombination, environmental adaptation, and speciation. All animals with bilateral symmetry inherited a genome structure from their last common ancestor that has been highly conserved in some taxa but seemingly unconstrained in others. However, the evolutionary forces driving these differences and the processes by which they emerge have remained largely uncharacterized. Here, we analyze genome organization across the phylum Annelida using 23 chromosome-level annelid genomes. We find that while many annelid lineages have maintained the conserved bilaterian genome structure, the Clitellata, a group containing leeches and earthworms, possesses completely scrambled genomes. We develop a rearrangement index to quantify the extent of genome structure evolution and show that, compared to the last common ancestor of bilaterians, leeches and earthworms have among the most highly rearranged genomes of any currently sampled species. We further show that bilaterian genomes can be classified into two distinct categories-high and low rearrangement-largely influenced by the presence or absence, respectively, of chromosome fission events. Our findings demonstrate that animal genome structure can be highly variable within a phylum and reveal that genome rearrangement can occur both in a gradual, stepwise fashion, or rapid, all-encompassing changes over short evolutionary timescales.

Ancestral TALE homeobox protein transcription factor regulates actin dynamics and cellular activities of protozoan parasite Entamoeba invadens.

Entamoeba histolytica causes invasive amoebiasis, an important neglected tropical disease with a significant global health impact. The pathogenicity and survival of E. histolytica and its reptilian equivalent, Entamoeba invadens, relies on its ability to exhibit efficient motility, evade host immune responses, and exploit host resources, all of which are governed by the actin cytoskeleton remodeling. Our study demonstrates the early origin and the regulatory role of TALE homeobox protein EiHbox1 in actin-related cellular processes. Several genes involved in different biological pathways, including actin dynamics are differentially expressed in EiHbox1 silenced cells. EiHbox1 silenced parasites showed disrupted F-actin organization and loss of cellular polarity. EiHbox1's presence in the anterior region of migrating cells further suggests its involvement in maintaining cellular polarity. Loss of polarized morphology of EiHbox1 silenced parasites leads to altered motility from fast, directionally persistent, and highly chemotactic to slow, random, and less chemotactic, which subsequently leads to defective aggregation during encystation. EiHbox1 knockdown also resulted in a significant reduction in phagocytic capacity and poor capping response. These findings highlight the importance of EiHbox1 of E. invadens in governing cellular processes crucial for their survival, pathogenicity, and evasion of the host immune system.

Structural Variation in Cancer: Role, Prevalence, and Mechanisms.

Somatic rearrangements resulting in genomic structural variation drive malignant phenotypes by altering the expression or function of cancer genes. Pan-cancer studies have revealed that structural variants (SVs) are the predominant class of driver mutation in most cancer types, but because they are difficult to discover, they remain understudied when compared with point mutations. This review provides an overview of the current knowledge of somatic SVs, discussing their primary roles, prevalence in different contexts, and mutational mechanisms. SVs arise throughout the life history of cancer, and 55% of driver mutations uncovered by the Pan-Cancer Analysis of Whole Genomes project represent SVs. Leveraging the convergence of cell biology and genomics, we propose a mechanistic classification of somatic SVs, from simple to highly complex DNA rearrangement classes. The actions of DNA repair and DNA replication processes together with mitotic errors result in a rich spectrum of SV formation processes, with cascading effects mediating extensive structural diversity after an initiating DNA lesion has formed. Thanks to new sequencing technologies, including the sequencing of single-cell genomes, open questions about the molecular triggers and the biomolecules involved in SV formation as well as their mutational rates can now be addressed.

A reverse genetics and genomics approach to gene paralog function and disease: Myokymia and the juxtaparanode.

The leucine-rich glioma-inactivated (LGI) family consists of four highly conserved paralogous genes, LGI1-4, that are highly expressed in mammalian central and/or peripheral nervous systems. LGI1 antibodies are detected in subjects with autoimmune limbic encephalitis and peripheral nerve hyperexcitability syndromes (PNHSs) such as Isaacs and Morvan syndromes. Pathogenic variations of LGI1 and LGI4 are associated with neurological disorders as disease traits including familial temporal lobe epilepsy and neurogenic arthrogryposis multiplex congenita 1 with myelin defects, respectively. No human disease has been reported associated with either LGI2 or LGI3. We implemented exome sequencing and family-based genomics to identify individuals with deleterious variants in LGI3 and utilized GeneMatcher to connect practitioners and researchers worldwide to investigate the clinical and electrophysiological phenotype in affected subjects. We also generated Lgi3-null mice and performed peripheral nerve dissection and immunohistochemistry to examine the juxtaparanode LGI3 microarchitecture. As a result, we identified 16 individuals from eight unrelated families with loss-of-function (LoF) bi-allelic variants in LGI3. Deep phenotypic characterization showed LGI3 LoF causes a potentially clinically recognizable PNHS trait characterized by global developmental delay, intellectual disability, distal deformities with diminished reflexes, visible facial myokymia, and distinctive electromyographic features suggestive of motor nerve instability. Lgi3-null mice showed reduced and mis-localized Kv1 channel complexes in myelinated peripheral axons. Our data demonstrate bi-allelic LoF variants in LGI3 cause a clinically distinguishable disease trait of PNHS, most likely caused by disturbed Kv1 channel distribution in the absence of LGI3.

RABV induces biphasic actin cytoskeletal rearrangement through Rac1 activity modulation.

Rabies virus (RABV) is highly lethal and triggers severe neurological symptoms. The neuropathogenic mechanism remains poorly understood. Ras-related C3 botulinum toxin substrate 1 (Rac1) is a Rho-GTPase that is involved in actin remodeling and has been reported to be closely associated with neuronal dysfunction. In this study, by means of a combination of pharmacological inhibitors, small interfering RNA, and specific dominant-negatives, we characterize the crucial roles of dynamic actin and the regulatory function of Rac1 in RABV infection, dominantly in the viral entry phase. The data show that the RABV phosphoprotein interacts with Rac1. RABV phosphoprotein suppress Rac1 activity and impedes downstream Pak1-Limk1-Cofilin1 signaling, leading to the disruption of F-actin-based structure formation. In early viral infection, the EGFR-Rac1-signaling pathway undergoes a biphasic change, which is first upregulated and subsequently downregulated, corresponding to the RABV entry-induced remodeling pattern of F-actin. Taken together, our findings demonstrate for the first time the role played by the Rac1 signaling pathway in RABV infection and may provide a clue for an explanation for the etiology of rabies neurological pathogenesis.IMPORTANCEThough neuronal dysfunction is predominant in fatal rabies, the detailed mechanism by which rabies virus (RABV) infection causes neurological symptoms remains in question. The actin cytoskeleton is involved in numerous viruses infection and plays a crucial role in maintaining neurological function. The cytoskeletal disruption is closely associated with abnormal nervous symptoms and induces neurogenic diseases. In this study, we show that RABV infection led to the rearrangement of the cytoskeleton as well as the biphasic kinetics of the Rac1 signal transduction. These results help elucidate the mechanism that causes the aberrant neuronal processes by RABV infection and may shed light on therapeutic development aimed at ameliorating neurological disorders.

Japanese encephalitis virus NS1 and NS1' proteins induce vimentin rearrangement via the CDK1-PLK1 axis to promote viral replication.

The host cytoskeleton plays crucial roles in various stages of virus infection, including viral entry, transport, replication, and release. However, the specific mechanisms by which intermediate filaments are involved in orthoflavivirus infection have not been well understood. In this study, we demonstrate that the Japanese encephalitis virus (JEV) remodels the vimentin network, resulting in the formation of cage-like structures that support viral replication. Mechanistically, JEV NS1 and NS1' proteins induce the translocation of CDK1 from the nucleus to the cytoplasm and interact with it, leading to the phosphorylation of vimentin at Ser56. This phosphorylation event recruits PLK1, which further phosphorylates vimentin at Ser83. Consequently, these phosphorylation modifications convert the typically filamentous vimentin into non-filamentous "particles" or "squiggles." These vimentin "particles" or "squiggles" are then transported retrogradely along microtubules to the endoplasmic reticulum, where they form cage-like structures. Notably, NS1' is more effective than NS1 in triggering the CDK1-PLK1 cascade response. Overall, our study provides new insights into how JEV NS1 and NS1' proteins manipulate the vimentin network to facilitate efficient viral replication. IMPORTANCE: Japanese encephalitis virus (JEV) is a mosquito-borne orthoflavivirus that causes severe encephalitis in humans, particularly in Asia. Despite the availability of a safe and effective vaccine, JEV infection remains a significant public health threat due to limited vaccination coverage. Understanding the interactions between JEV and host proteins is essential for developing more effective antiviral strategies. In this study, we investigated the role of vimentin, an intermediate filament protein, in JEV replication. Our findings reveal that JEV NS1 and NS1' proteins induce vimentin rearrangement, resulting in the formation of cage-like structures that envelop the viral replication factories (RFs), thus facilitating efficient viral replication. Our research highlights the importance of the interplay between the cytoskeleton and orthoflavivirus, suggesting that targeting vimentin could be a promising approach for the development of antiviral strategies to inhibit JEV propagation.

The Rac1-PAK1-Arp2/3 signaling axis regulates CHIKV nsP1-induced filopodia and optimal viral genome replication.

Alphavirus infection induces dramatic remodeling of host cellular membranes, producing filopodia-like and intercellular extensions. The formation of filopodia-like extensions has been primarily assigned to the replication protein nsP1, which binds and reshapes the host plasma membrane when expressed alone. While reported decades ago, the molecular mechanisms behind nsP1 membrane deformation remain unknown. Using mammalian epithelial cells and Chikungunya virus (CHIKV) as models, we characterized nsP1-induced membrane deformations as highly dynamic actin-rich lamellipodia and filopodia-like extensions. Through pharmacological inhibition and genetic invalidation, we identified the critical contribution of the Rac1 GTPase and its downstream effectors PAK1 and the actin nucleator Arp2 in nsP1-induced membrane deformation. An intact Rac1-PAK1-Arp2 signaling axis was also required for optimal CHIKV genome replication. Therefore, our results designate the Rac1-PAK1-Arp2 pathway as an essential signaling node for CHIKV infection and establish a parallel requirement for host factors involved in nsP1-induced plasma membrane reshaping and assembly of a functional replication complex.IMPORTANCEThe alphavirus nsP1 protein dramatically remodels host cellular membranes, resulting in the formation of filopodia-like extensions. Although described decades ago, the molecular mechanisms controlling these membrane deformations and their functional importance remain elusive. Our study provides mechanistic insight, uncovering the critical role of the Rac1 GTPase, along with its downstream effectors PAK1 and the actin nucleator Arp2, in the nsP1-associated phenotype. Furthermore, we demonstrate that the Rac1-PAK1-Arp2 pathway is essential for optimal CHIKV genome replication. Our findings establish a parallel in the cellular mechanisms governing nsP1-induced plasma membrane reshaping and the production of a functional replication complex in infected cells.

The cryptic complex rearrangements involving the DMD gene: etiologic clues about phenotypical differences revealed by optical genome mapping.

BACKGROUND: Deletion or duplication in the DMD gene is one of the most common causes of Duchenne and Becker muscular dystrophy (DMD/BMD). However, the pathogenicity of complex rearrangements involving DMD, especially segmental duplications with unknown breakpoints, is not well understood. This study aimed to evaluate the structure, pattern, and potential impact of rearrangements involving DMD duplication. METHODS: Two families with DMD segmental duplications exhibiting phenotypical differences were recruited. Optical genome mapping (OGM) was used to explore the cryptic pattern of the rearrangements. Breakpoints were validated using long-range polymerase chain reaction combined with next-generation sequencing and Sanger sequencing. RESULTS: A multi-copy duplication involving exons 64-79 of DMD was identified in Family A without obvious clinical symptoms. Family B exhibited typical DMD neuromuscular manifestations and presented a duplication involving exons 10-13 of DMD. The rearrangement in Family A involved complex in-cis tandem repeats shown by OGM but retained a complete copy (reading frame) of DMD inferred from breakpoint validation. A reversed insertion with a segmental repeat was identified in Family B by OGM, which was predicted to disrupt the normal structure and reading frame of DMD after confirming the breakpoints. CONCLUSIONS: Validating breakpoint and rearrangement pattern is crucial for the functional annotation and pathogenic classification of genomic structural variations. OGM provides valuable insights into etiological analysis of DMD/BMD and enhances our understanding for cryptic effects of complex rearrangements.

Structural rearrangements as a recurrent pathogenic mechanism for SETBP1 haploinsufficiency.

Chromosomal structural rearrangements consist of anomalies in genomic architecture that may or may not be associated with genetic material gain and loss. Evaluating the precise breakpoint is crucial from a diagnostic point of view, highlighting possible gene disruption and addressing to appropriate genotype-phenotype association. Structural rearrangements can either occur randomly within the genome or present with a recurrence, mainly due to peculiar genomic features of the surrounding regions. We report about three non-related individuals, harboring chromosomal structural rearrangements interrupting SETBP1, leading to gene haploinsufficiency. Two out of them resulted negative to Chromosomal Microarray Analysis (CMA), being the rearrangement balanced at a microarray resolution. The third one, presenting with a complex three-chromosome rearrangement, had been previously diagnosed with SETBP1 haploinsufficiency due to a partial gene deletion at one of the chromosomal breakpoints. We thoroughly characterized the rearrangements by means of Optical Genome Mapping (OGM) and Whole Genome Sequencing (WGS), providing details about the involved sequences and the underlying mechanisms. We propose structural variants as a recurrent event in SETBP1 haploinsufficiency, which may be overlooked by laboratory routine genomic analyses (CMA and Whole Exome Sequencing) or only partially determined when associated with genomic losses at breakpoints. We finally introduce a possible role of SETBP1 in a Noonan-like phenotype.

NF2-related schwannomatosis and other schwannomatosis: an updated genetic and epidemiological study.

OBJECTIVES: New diagnostic criteria for NF2-related schwannomatosis (NF2) were published in 2022. An updated UK prevalence was generated in accordance with these, with an emphasis on the rate of de novo NF2 (a 50% frequency is widely quoted in genetic counselling). The distribution of variant types among de novo and familial NF2 cases was also assessed. METHODS: The UK National NF2 database identifies patients meeting updated NF2 criteria from a highly ascertained population cared for by England's specialised service. Diagnostic prevalence was assessed on 1 February 2023. Molecular analysis of blood and, where possible, tumour specimens for NF2, LZTR1 and SMARCB1 was performed. RESULTS: 1084 living NF2 patients were identified on prevalence day (equivalent to 1 in 61 332). The proportion with NF2 inherited from an affected parent was only 23% in England. If people without a confirmed molecular diagnosis or bilateral vestibular schwannoma are excluded, the frequency of de novo NF2 remains high (72%). Of the identified de novo cases, almost half were mosaic. The most common variant type was nonsense variants, accounting for 173/697 (24.8%) of people with an established variant, but only 18/235 (7.7%) with an inherited NF2 pathogenic variant (p<0.0001). Missense variants had the highest proportion of familial association (56%). The prevalence of LZTR1-related schwannomatosis and SMARCB1-related schwannomatosis was 1 in 527 000 and 1 in 1.1M, respectively, 8.4-18.4 times lower than NF2. CONCLUSIONS: This work confirms a much higher rate of de novo NF2 than previously reported and highlights the benefits of maintaining patient databases for accurate counselling.