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Supp Tables S1-S6 (including variant classification, bioinformatics predictions versus experimental data, primer sequences, summary of biological, clinical, tumoral, familial and multifactorial data, and description of statistical analysis approaches)

BRCA2 is a clinically actionable gene implicated in breast and ovarian cancer predisposition that has become a high priority target for improving the classification of variants of unknown significance (VUS). Among all BRCA2 VUS, those causing partial/leaky splicing defects are the most challenging to classify because the minimal level of full-length (FL) transcripts required for normal function remains to be established. Here, we explored BRCA2 exon 3 (BRCA2e3) as a model for calibrating variant-induced spliceogenicity and estimating thresholds for BRCA2 haploinsufficiency. In silico predictions, minigene splicing assays, patients' RNA analyses, a mouse embryonic stem cell (mESC) complementation assay and retrieval of patient-related information were combined to determine the minimal requirement of FL BRCA2 transcripts. Of 100 BRCA2e3 variants tested in the minigene assay, 64 were found to be spliceogenic, causing mild to severe RNA defects. Splicing defects were also confirmed in patients' RNA when available. Analysis of a neutral leaky variant (c.231T>G) showed that a reduction of approximately 60% of FL BRCA2 transcripts from a mutant allele does not cause any increase in cancer risk. Moreover, data obtained from mESCs suggest that variants causing a decline in FL BRCA2 with approximately 30% of wild-type are not pathogenic, given that mESCs are fully viable and resistant to DNA-damaging agents in those conditions. In contrast, mESCs producing lower relative amounts of FL BRCA2 exhibited either null or hypomorphic phenotypes. Overall, our findings are likely to have broader implications on the interpretation of BRCA2 variants affecting the splicing pattern of other essential exons.Significance:These findings demonstrate that BRCA2 tumor suppressor function tolerates substantial reduction in full-length transcripts, helping to determine the pathogenicity of BRCA2 leaky splicing variants, some of which may not increase cancer risk.

Supplementary Tables S1-S4. Table S1. Description of primers used in this study. Table S2. Variants selected in BRCA2 exon 12 and its flanking intronic regions. Table S3. Overview of bioinformatics predictions and experimental data obtained for the 40 selected BRCA2 exon 12 variants. Table S4. Clinical and family data of patients carrying BRCA2 exon 12 spliceogenic variants.

Fig. S1 to S10. Figure S1. Variant selection from human variation databases; Figure S2. Capillary electrophoresis analyses of BRCA2 exon 12 splicing patterns in minigene assays of presumed LoF variants; Figure S3. Bioinformatics predictions of 3'/5' ss alterations for variants located at position IVS{plus minus}1/2 of BRCA2 exon 12; Figure S4. Bioinformatics analysis of variants predicted to alter 3'/5' ss of BRCA2 exon 12 (â^†MES {less than or equal to} -15%); Figure S5. Capillary electrophoresis analyses of BRCA2 exon 12 splicing patterns in minigene assays of variants predicted to alter 3'/5' ss (A) or ESR (B); Figure S6. Capillary electrophoresis analyses of BRCA2 exon 12 splicing patterns in control and patient lymphoblastoid cell lines; Figure S7. RT-PCR analysis of BRCA2 exon 12 splicing patterns in puromycin- or mock-treated lymphoblastoid cell lines of control individuals and patients carrying the c.6844G>T or c.6901G>T nonsense variants; Figure S8. Capillary electrophoresis analyses of BRCA2 exon 12 splicing patterns in variant-expressing mESC; Figure S9. Quantitation of BRCA2 protein expression in mESC; Figure S10. Sensitivity of BRCA2 variants to cisplatin and PARP inhibitors.

Germline nonsense and canonical splice site variants identified in disease-causing genes are generally considered as loss-of-function (LoF) alleles and classified as pathogenic. However, a fraction of such variants could maintain function through their impact on RNA splicing. To test this hypothesis, we used the alternatively spliced BRCA2 exon 12 (E12) as a model system because its in-frame skipping leads to a potentially functional protein. All E12 variants corresponding to putative LoF variants or predicted to alter splicing (n = 40) were selected from human variation databases and characterized for their impact on splicing in minigene assays and, when available, in patient lymphoblastoid cell lines. Moreover, a selection of variants was analyzed in a mouse embryonic stem cell–based functional assay. Using these complementary approaches, we demonstrate that a subset of variants, including nonsense variants, induced in-frame E12 skipping through the modification of splice sites or regulatory elements and, consequently, led to an internally deleted but partially functional protein. These data provide evidence, for the first time in a cancer-predisposition gene, that certain presumed null variants can retain function due to their impact on splicing. Further studies are required to estimate cancer risk associated with these hypomorphic variants. More generally, our findings highlight the need to exercise caution in the interpretation of putative LoF variants susceptible to induce in-frame splicing modifications.Significance:This study presents evidence that certain presumed loss-of-function variants in a cancer predisposition gene can retain function due to their direct impact on RNA splicing.

Hereditary Hemorrhagic Telangiectasia (HHT) is a rare vascular disorder causing abnormal vessel formation and characterized by autosomal dominant transmission. The associated considerable variability in symptoms and clinical severity complicate the management of the disease. In clinical routine, 3 main genes,ACVRL1(also known asALK1),ENGandSMAD4are screened for pathogenic variants at the origin of HHT. About 80% of HHT cases are caused by pathogenic coding variants inACVRL1andENG. However, at least 15% remain with no molecular explanations in the 3 main genes. We here report the identification of 2 never reported variants, c.-79C>T and c.-68G>A, in the 5’UTR ofENGin 2 unrelated HHT patients. These 2 variants are predicted to create upstream AUGs (uAUGs) in the 5’UTR, which are in frame with a stop codon located within the CoDing Sequence (CDS), thus generating Overlapping upstream Open reading frames (uoORFs). In other cases, uAUGs can lead to fully upstream ORFs (uORFs) when associated with stop codons located within the 5’UTR or to elongated CDS (eCDS) when in frame with the CDS and associated with the main stop codon.In order to assess the pathogenicity of theseENGvariants, we performedin vitrofunctional assays based on the expression of wild-type and mutant constructs in human cells. We found that these 5’UTRENGvariants were associated with a decrease of protein levels in HeLa and HUVEC cells. They were also associated with a decreased ability to activate BMP9-stimulated ALK1 receptor in a BMP-response element (BRE) assay. This assay is a mandatory element before providing a definitive molecular diagnosis and has been so far applied only on codingENGvariants. We applied the same experimental workflow on 3 additional uoORF-creating variants (c.-142A>T, c.-127C>T and c.-10C>T) and one eCDS-creating variant (c.-9G>A) in the 5’UTR ofENGpreviously reported in HHT patients. We found that all the analysed uoORF-creating variants alter endoglin levels and function. A comparison of our experimental results with patients’ clinical characteristics suggests that uoORF-creating variants leading to ENG protein levels ≤ 40%in vitrowould be associated with HHT. Additional experiments relying on an artificial deletion in our mutated constructs show that created uAUGs predicted to create uoORFs are able to initiate the translation indicating that the associated effect is likely caused by an alteration of the translation mechanism.Overall, we here identified two never reported 5’UTRENGvariations in HHT patients and shed new lights on the role of upstream ORFs on ENG regulation. Our findings contribute to the amelioration of molecular diagnosis in HHT.

Modeling splicing is essential for tackling the challenge of variant interpretation as each nucleotide variation can be pathogenic by affecting pre-mRNA splicing via disruption/creation of splicing motifs such as 5’/3’ splice sites, branch sites or splicing regulatory elements. Unfortunately, most in silico tools focus on a specific type of splicing motif, which is why we developed the Splicing Prediction Pipeline (SPiP) to perform, in one single bioinformatic analysis based on machine learning approach, comprehensive assessment of variant effect on different splicing motifs. We gathered a curated set of 4,616 variants scattered all along the sequence of 227 genes, with their corresponding splicing studies. Bayesian analysis provided us the number of control variants, i.e. variants without impact on splicing, to mimic the deluge of variants from high throughput sequencing data. Results show that SPiP can deal with the diversity of splicing alterations, with 83.13% sensitivity and 99% specificity to detect spliceogenic variants. Overall performance as measured by area under the receiving operator curve was 0.986, significantly better than 0.965 spliceAI for the same dataset. SPiP lends itself to a unique suite for comprehensive prediction of spliceogenicity in the genomic medicine era. SPiP is available at: [https://sourceforge.net/projects/splicing-prediction-pipeline/](https://sourceforge.net/projects/splicing-prediction-pipeline/)

Germline pathogenic variants in the DNA mismatch repair genes (MMR): MLH1, MSH2, MSH6, and PMS2, are causative of Lynch syndrome (LS). However, many of the variants mapping outside the invariant splice site positions (IVS ± 1, IVS ± 2) are classified as variants of unknown significance (VUS). Three such variants (MLH1 c.588+5G>C, c.588+5G>T and c.677+5G>A) were identified in 8 unrelated LS families from Argentina, Brazil and Chile. Herein, we collected clinical information on these families and performed segregation analysis and RNA splicing studies to assess the implication of these VUS in LS etiology. Pedigrees showed a clear pattern of variant co-segregation with colorectal cancer and/or other LS-associated malignancies. Tumors presented deficient expression of MLH1-PMS2 proteins in 7/7 of the LS families, and MSI-high status in 3/3 cases. Moreover, RNA analyses revealed that c.588+5G>C and c.588+5G>T induce skipping of exon 7 whereas c.677+5G>A causes skipping of exon 8. In sum, we report that the combined clinical findings in the families and the molecular studies provided the evidences needed to demonstrate that the three MLH1 variants are causative of LS and to classify c.588+5G>C and c.677+5G>A as class 5 (pathogenic), and c.588+5G>T as class 4 (likely-pathogenic). Our findings underline the importance of performing clinical and family analyses, as well as RNA splicing assays in order to determine the clinical significance of intronic variants, and contribute to the genetic counseling and clinical management of patients and their relatives.

ABCC8 encodes the SUR1 subunit of the β-cell ATP-sensitive potassium channel whose loss of function causes congenital hyperinsulinism (CHI). Molecular diagnosis is critical for optimal management of CHI patients. Unfortunately, assessing the impact of ABCC8 variants on RNA splicing remains very challenging as this gene is poorly expressed in leukocytes. Here, we performed bioinformatics analysis and cell-based minigene assays to assess the impact on splicing of 13 ABCC8 variants identified in 20 CHI patients. Next, channel properties of SUR1 proteins expected to originate from minigene-detected in-frame splicing defects were analyzed after ectopic expression in COSm6 cells. Out of the analyzed variants, seven induced out-of-frame splicing defects and were therefore classified as recessive pathogenic, whereas two led to skipping of in-frame exons. Channel functional analysis of the latter demonstrated their pathogenicity. Interestingly, the common rs757110 SNP increased exon skipping in our system suggesting that it may act as a disease modifier factor. Our strategy allowed determining the pathogenicity of all selected ABCC8 variants, and CHI-inheritance pattern for 16 out of the 20 patients. This study highlights the value of combining RNA and protein functional approaches in variant interpretation and reveals the minigene splicing assay as a new tool for CHI molecular diagnostics.

Venous thromboembolism is the third common cardiovascular disease and is composed of two entities, deep vein thrombosis (DVT) and its fatal form, pulmonary embolism (PE). While PE is observed in ∼40% of patients with documented DVT, there is limited biomarkers that can help identifying patients at high PE risk.To fill this need, we implemented a two hidden-layers artificial neural networks (ANN) on 376 antibodies and 19 biological traits measured in the plasma of 1388 DVT patients, with or without PE, of the MARTHA study. We used the LIME algorithm to obtain a linear approximate of the resulting ANN prediction model. As MARTHA patients were typed for genotyping DNA arrays, a genome wide association study (GWAS) was conducted on the LIME estimate. Detected single nucleotide polymorphisms (SNPs) were tested for association with PE risk in MARTHA. Main findings were replicated in the EOVT study composed of 143 PE patients and 196 DVT only patients.The derived ANN model for PE achieved an accuracy of 0.89 and 0.79 in our training and testing sets, respectively. A GWAS on the LIME approximate identified a strong statistical association peak (p = 5.3×10−7) at the PLXNA4 locus, with lead SNP rs1424597 at which the minor A allele was further shown to associate with an increased risk of PE (OR = 1.49 [1.12 – 1.98], p = 6.1×10−3). Further association analysis in EOVT revealed that, in the combined MARTHA and EOVT samples, the rs1424597-A allele was associated with increased PE risk (OR = 1.74 [1.27 – 2.38, p = 5.42×10−4) in patients over 37 years of age but not in younger patients (OR = 0.96 [0.65 – 1.41], p = 0.848).Using an original integrated proteomics and genetics strategy, we identified PLXNA4 as a new susceptibility gene for PE whose exact role now needs to be further elucidated.Author SummaryPulmonary embolism is a severe and potentially fatal condition characterized by the presence of a blood clot (or thrombus) in the pulmonary artery. Pulmonary embolism is often the consequence of the migration of a thrombus from a deep vein to the lung. Together with deep vein thrombosis, pulmonary embolism forms the so-called venous thromboembolism, the third most common cardiovascular disease, and its prevalence strongly increases with age. While pulmonary embolism is observed in ∼40% of patients with deep vein thrombosis, there is currenly limited biomarkers that can help predicting which patients with deep vein thrombosis are at risk of pulmonary embolism. We here deployed an Artificial Intelligence based methodology integrating both plasma proteomics and genetics data to identify novel biomarkers for PE. We thus identified the PLXNA4 gene as a novel molecular player involved in the pathophysiology of pulmonary embolism. In particular, using two independent cohorts totalling 1,881 patients with venous thromboembolism among which 467 experienced pulmonary embolism, we identified a genetic polymorphism in the PLXNA4 gene that associates with ∼2 fold increased risk of pulmonary embolism in patients aged more than ∼40 years.

Discriminating which nucleotide variants cause disease or contribute to phenotypic traits remains a major challenge in human genetics. In theory, any intragenic variant can potentially affect RNA splicing by altering splicing regulatory elements (SREs). However, these alterations are often ignored mainly because pioneer SRE predictors have proved inefficient. Here, we report the first large-scale comparative evaluation of four user-friendly SRE-dedicated algorithms (QUEPASA, HEXplorer, SPANR, and HAL) tested both as standalone tools and in multiple combined ways based on two independent benchmark datasets adding up to >1,300 exonic variants studied at the messenger RNA level and mapping to 89 different disease-causing genes. These methods display good predictive power, based on decision thresholds derived from the receiver operating characteristics curve analyses, with QUEPASA and HAL having the best accuracies either as standalone or in combination. Still, overall there was a tight race between the four predictors, suggesting that all methods may be of use. Additionally, QUEPASA and HEXplorer may be beneficial as well for predicting variant-induced creation of pseudoexons deep within introns. Our study highlights the potential of SRE predictors as filtering tools for identifying disease-causing candidates among the plethora of variants detected by high-throughput DNA sequencing and provides guidance for their use in genomic medicine settings.

BRCA2 is a clinically actionable gene implicated in breast and ovarian cancer predisposition that has become a high priority target for improving the classification of variants of unknown significance (VUS). Among all BRCA2 VUS, those causing partial/leaky splicing defects are the most challenging to classify because the minimal level of full-length (FL) transcripts required for normal function remains to be established. Here, we explored BRCA2 exon 3 (BRCA2e3) as a model for calibrating variant-induced spliceogenicity and estimating thresholds for BRCA2 haploinsufficiency. In silico predictions, minigene splicing assays, patients' RNA analyses, a mouse embryonic stem cell (mESC) complementation assay and retrieval of patient-related information were combined to determine the minimal requirement of FL BRCA2 transcripts. Of 100 BRCA2e3 variants tested in the minigene assay, 64 were found to be spliceogenic, causing mild to severe RNA defects. Splicing defects were also confirmed in patients' RNA when available. Analysis of a neutral leaky variant (c.231T>G) showed that a reduction of approximately 60% of FL BRCA2 transcripts from a mutant allele does not cause any increase in cancer risk. Moreover, data obtained from mESCs suggest that variants causing a decline in FL BRCA2 with approximately 30% of wild-type are not pathogenic, given that mESCs are fully viable and resistant to DNA-damaging agents in those conditions. In contrast, mESCs producing lower relative amounts of FL BRCA2 exhibited either null or hypomorphic phenotypes. Overall, our findings are likely to have broader implications on the interpretation of BRCA2 variants affecting the splicing pattern of other essential exons. Significance: These findings demonstrate that BRCA2 tumor suppressor function tolerates substantial reduction in full-length transcripts, helping to determine the pathogenicity of BRCA2 leaky splicing variants, some of which may not increase cancer risk.

Germline nonsense and canonical splice site variants identified in disease-causing genes are generally considered as loss-of-function (LoF) alleles and classified as pathogenic. However, a fraction of such variants could maintain function through their impact on RNA splicing. To test this hypothesis, we used the alternatively spliced BRCA2 exon 12 (E12) as a model system because its in-frame skipping leads to a potentially functional protein. All E12 variants corresponding to putative LoF variants or predicted to alter splicing (n = 40) were selected from human variation databases and characterized for their impact on splicing in minigene assays and, when available, in patient lymphoblastoid cell lines. Moreover, a selection of variants was analyzed in a mouse embryonic stem cell–based functional assay. Using these complementary approaches, we demonstrate that a subset of variants, including nonsense variants, induced in-frame E12 skipping through the modification of splice sites or regulatory elements and, consequently, led to an internally deleted but partially functional protein. These data provide evidence, for the first time in a cancer-predisposition gene, that certain presumed null variants can retain function due to their impact on splicing. Further studies are required to estimate cancer risk associated with these hypomorphic variants. More generally, our findings highlight the need to exercise caution in the interpretation of putative LoF variants susceptible to induce in-frame splicing modifications. Significance: This study presents evidence that certain presumed loss-of-function variants in a cancer predisposition gene can retain function due to their direct impact on RNA splicing.

SummaryVariants in 5’UTR regions that create upstream translation initiation AUG codons are a class of neglected non coding variations. When they associate with a premature stop codon and create upstream open reading frames (uORFs) whose translation competes with that of natural proteins, they can have strong impact on human diseases. We here describe MORFEE, a new bioinformatics tool that detects, annotates and predicts, from a standard VCF file, the creation of uORF by any 5’UTR variants on uORF creation. MORFEE was applied to two genomic resources and identified candidate functional variants that could explain statistical association signals observed in the context of Genome Wide Association Studies or could be responsible for rare forms of diseases. In conclusion MORFEE is an easy-to-use tool complementary to existing ones that can help resolving genetic investigations that remained so far unfruitful.Availability and implementationMORFEE is written in R with code and package available at https://github.com/daissi/MORFEE.Contactdavid-alexandre.tregouet@inserm.fr; david-alexandre.tregouet@u-bordeaux.fr

SummaryInherited Protein S deficiency (PSD) (MIM176880) is a rare automosal dominant disorder caused by rare mutations, mainly located in the coding sequence of the structuralPROS1gene, and associated with an increased risk of venous thromboembolism. To identify the molecular defect underlying PSD observed in an extended French pedigree with 7 PSD affected members in who no candidate deleteriousPROS1mutation was detected by Sanger sequencing ofPROS1exons and their flanking intronic regions or via a MLPA approach, a whole genome sequencing strategy was adopted. This led to the identification of a never reported C to T substitution at c.-39 from the natural ATG codon of thePROS1gene that completely segregates with PSD in the whole family. This substitution ACG->ATG creates a new start codon upstream of the main ATG. We experimentally demonstrated that the variant generates a novel overlapping ORF and inhibits the translation of the wild type protein from the main ORF in HeLa cells. This work describes the first example of 5’UTRPROS1mutation causing PSD through the creation of an upstream ORF, a mutation that is not predicted to be deleterious by standard annotation softwares.

Germline nonsense and canonical splice site variants identified in disease-causing genes are generally considered as loss-of-function (LoF) alleles and classified as pathogenic. However, a fraction of such variants could maintain function through their impact on RNA splicing. To test this hypothesis, we used the alternatively spliced

A recent analysis using family history weighting and co-observation classification modeling indicated that BRCA1 c.594-2A>C (IVS9-2A>C), previously described to cause exon 10 skipping (a truncating alteration), displays characteristics inconsistent with those of a high risk pathogenic BRCA1 variant. We used large-scale genetic and clinical resources from the ENIGMA, CIMBA and BCAC consortia to assess pathogenicity of c.594-2A>C. The combined odds for causality considering case-control, segregation, and breast tumor pathology information was 3.23x10-8. Our data indicate that c.594-2A>C is always in cis with c.641A>G.The spliceogenic effect of c.[594-2A>C;641A>G] was characterized using RNA analysis of human samples and splicing minigenes. As expected, c.[594-2A>C; 641A>G] caused exon 10 skipping, albeit not due to c.594-2A>C impairing the acceptor site but rather by c.641A>G modifying exon 10 splicing regulatory element(s). Multiple blood-based RNA assays indicated that the variant allele did not produce detectable levels of full-length transcripts, with a per allele BRCA1 expression profile comprised of ?70-80% truncating transcripts, and ?20-30% of in-frame ?9,10 transcripts predicted to encode a BRCA1 protein with tumor suppression function.We confirm that BRCA1c.[594-2A>C;641A>G] should not be considered a high-risk pathogenic variant. Importantly, results from our detailed mRNA analysis suggest that BRCA-associated cancer risk is likely not markedly increased for individuals who carry a truncating variant in BRCA1 exons 9 or 10, or any other BRCA1 allele that permits 20-30% of tumor suppressor function. More generally, our findings highlight the importance of assessing naturally occurring alternative splicing for clinical evaluation of variants in disease-causing genes.

International audience; Primary microcephaly is a neurodevelopmental disorder that is caused by a reduction in brain size as a result of defects in the proliferation of neural progenitor cells during development. Mutations in genes encoding proteins that localize to the mitotic spindle and centrosomes have been implicated in the pathogenicity of primary microcephaly. In contrast, the contractile ring and midbody required for cytokinesis, the final stage of mitosis, have not previously been implicated by human genetics in the molecular mechanisms of this phenotype. Citron kinase (CIT) is a multi-domain protein that localizes to the cleavage furrow and midbody of mitotic cells, where it is required for the completion of cytokinesis. Rodent models of Cit deficiency highlighted the role of this gene in neurogenesis and microcephaly over a decade ago. Here, we identify recessively inherited pathogenic variants in CIT as the genetic basis of severe microcephaly and neonatal death. We present postmortem data showing that CIT is critical to building a normally sized human brain. Consistent with cytokinesis defects attributed to CIT, multinucleated neurons were observed throughout the cerebral cortex and cerebellum of an affected proband, expanding our understanding of mechanisms attributed to primary microcephaly.

Pathogenicity assessment of DNA variants in disease genes to explain their clinical consequences is an integral component of diagnostic molecular testing. The International Society for Gastrointestinal Hereditary Tumors (InSiGHT) has developed specific criteria for the interpretation of mismatch repair (MMR) gene variants. Here, we performed a systematic investigation of 24 MLH1 and MSH2 variants. The assessments were done by analyzing population frequency, segregation, tumor molecular characteristics, RNA effects, protein expression levels and in vitro MMR activity. Classifications were confirmed for 15 variants and changed for 3, and for the first time determined for 6 novel variants. Overall, based on our results we propose the introduction of some refinements to the InSiGHT classification rules. The proposed changes have the advantage of homogenizing the InSIGHT interpretation criteria with those set out by the Evidence-based Network for the Interpretation of Germline Mutant Alleles (ENIGMA) consortium for the BRCA1/BRCA2 genes. We also observed that the addition of only few clinical data was sufficient to obtain a more stable classification for variants considered as "likely pathogenic" or "likely non pathogenic". This shows the importance of obtaining as many as possible points of evidence for variant interpretation, especially from the clinical setting. This article is protected by copyright. All rights reserved.