A method of predicting changes in human gene splicing induced by genetic variants in context of cis-acting elements.
ABSTRACT: BACKGROUND: Polymorphic variants and mutations disrupting canonical splicing isoforms are among the leading causes of human hereditary disorders. While there is a substantial evidence of aberrant splicing causing Mendelian diseases, the implication of such events in multi-genic disorders is yet to be well understood. We have developed a new tool (SpliceScan II) for predicting the effects of genetic variants on splicing and cis-regulatory elements. The novel Bayesian non-canonical 5'GC splice site (SS) sensor used in our tool allows inference on non-canonical exons. RESULTS: Our tool performed favorably when compared with the existing methods in the context of genes linked to the Autism Spectrum Disorder (ASD). SpliceScan II was able to predict more aberrant splicing isoforms triggered by the mutations, as documented in DBASS5 and DBASS3 aberrant splicing databases, than other existing methods. Detrimental effects behind some of the polymorphic variations previously associated with Alzheimer's and breast cancer could be explained by changes in predicted splicing patterns. CONCLUSIONS: We have developed SpliceScan II, an effective and sensitive tool for predicting the detrimental effects of genomic variants on splicing leading to Mendelian and complex hereditary disorders. The method could potentially be used to screen resequenced patient DNA to identify de novo mutations and polymorphic variants that could contribute to a genetic disorder.
Project description:The genetic heterogeneity of Mendelian disorders results in a significant proportion of patients that are unable to be assigned a confident molecular diagnosis after conventional exon sequencing and variant interpretation. Here, we evaluated how many patients with an inherited retinal disease (IRD) have variants of uncertain significance (VUS) that are disrupting splicing in a known IRD gene by means other than affecting the canonical dinucleotide splice site. Three in silico splice-affecting variant predictors were leveraged to annotate and prioritize variants for splicing functional validation. An in vitro minigene system was used to assay each variant's effect on splicing. Starting with 745 IRD patients lacking a confident molecular diagnosis, we validated 23 VUS as splicing variants that likely explain disease in 26 patients. Using our results, we optimized in silico score cutoffs to guide future variant interpretation. Variants that alter base pairs other than the canonical GT-AG dinucleotide are often not considered for their potential effect on RNA splicing but in silico tools and a minigene system can be utilized for the prioritization and validation of such splice-disrupting variants. These variants can be overlooked causes of human disease but can be identified using conventional exon sequencing with proper interpretation guidelines.
Project description:X-linked Dystonia-Parkinsonism (XDP) is a Mendelian neurodegenerative disease that is endemic to the Philippines and is associated with a founder haplotype. We integrated multiple genome and transcriptome assembly technologies to narrow the causal mutation to the TAF1 locus, which included a SINE-VNTR-Alu (SVA) retrotransposition into intron 32 of the gene. Transcriptome analyses identified decreased expression of the canonical cTAF1 transcript among XDP probands, and de novo assembly across multiple pluripotent stem-cell-derived neuronal lineages discovered aberrant TAF1 transcription that involved alternative splicing and intron retention (IR) in proximity to the SVA that was anti-correlated with overall TAF1 expression. CRISPR/Cas9 excision of the SVA rescued this XDP-specific transcriptional signature and normalized TAF1 expression in probands. These data suggest an SVA-mediated aberrant transcriptional mechanism associated with XDP and may provide a roadmap for layered technologies and integrated assembly-based analyses for other unsolved Mendelian disorders.
Project description:High-throughput sequencing efforts in molecular tumour diagnostics detect increasing numbers of novel variants, including variants predicted to affect splicing. In silico prediction tools can reliably predict the effect of variant disrupting canonical splice sites; however, experimental validation is required to confirm aberrant splicing. Here, we present RNA analysis performed for 13 canonical splice site variants predicted or known to result in splicing in the cancer predisposition genes MLH1, MSH2, MSH6, APC and BRCA1. Total nucleic acid was successfully isolated for 10 variants from eight formalin-fixed paraffin-embedded (FFPE) tumour tissues and two B-cell lines. Aberrant splicing was confirmed in all six variants known to result in splicing. Of one known variant in the B-cell line, aberrant splicing could only be detected after formalin fixation, which indicated that formalin fixation could possibly inhibit RNA degradation. Aberrant splicing was concluded in three of four predicted splice variants of uncertain significance, supporting their pathogenic effect. With this assay, somatic splice variants can be easily and rapidly analysed, enabling retrospective analysis to support the pathogenicity of variants predicted to result in splicing when only FFPE material is available.
Project description:Genetic variants that cause haploinsufficiency account for many autosomal dominant (AD) disorders. Gene-based diagnosis classifies variants that alter canonical splice signals as pathogenic, but due to imperfect understanding of RNA splice signals other variants that may create or eliminate splice sites are often clinically classified as variants of unknown significance (VUS). To improve recognition of pathogenic splice-altering variants in AD disorders, we used computational tools to prioritize VUS and developed a cell-based minigene splicing assay to confirm aberrant splicing. Using this two-step procedure we evaluated all rare variants in two AD cardiomyopathy genes, lamin A/C (LMNA) and myosin binding protein C (MYBPC3). We demonstrate that 13 LMNA and 35 MYBPC3 variants identified in cardiomyopathy patients alter RNA splicing, representing a 50% increase in the numbers of established damaging splice variants in these genes. Over half of these variants are annotated as VUS by clinical diagnostic laboratories. Familial analyses of one variant, a synonymous LMNA VUS, demonstrated segregation with cardiomyopathy affection status and altered cardiac LMNA splicing. Application of this strategy should improve diagnostic accuracy and variant classification in other haploinsufficient AD disorders.
Project description:ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) are a family of multidomain extracellular protease enzymes with 19 members. A growing number of ADAMTS family gene variants have been identified in patients with various hereditary diseases. To understand the genomic landscape and mutational spectrum of ADAMTS family genes, we evaluated all reported variants in the ClinVar database and Human Gene Mutation Database (HGMD), as well as recent literature on Mendelian hereditary disorders associated with ADAMTS family genes. Among 1089 variants in 14 genes reported in public databases, 307 variants previously suggested for pathogenicity in Mendelian diseases were comprehensively re-evaluated using the American College of Medical Genetics and Genomics (ACMG) 2015 guideline. A total of eight autosomal recessive genes were annotated as being strongly associated with specific Mendelian diseases, including two recently discovered genes (ADAMTS9 and ADAMTS19) for their causality in congenital diseases (nephronophthisis-related ciliopathy and nonsyndromic heart valve disease, respectively). Clinical symptoms and affected organs were extremely heterogeneous among hereditary diseases caused by ADAMTS family genes, indicating phenotypic heterogeneity despite their structural and functional similarity. ADAMTS6 was suggested as presenting undiscovered pathogenic mutations responsible for novel Mendelian disorders. Our study is the first to highlight the genomic landscape of ADAMTS family genes, providing an appropriate genetic approach for clinical use.
Project description:BACKGROUND:X-linked Alport syndrome (XLAS) is a progressive, hereditary glomerular nephritis of variable severity caused by pathogenic COL4A5 variants. Currently, genetic testing is widely used for diagnosing XLAS; however, determining the pathogenicity of variants detected by such analyses can be difficult. Intronic variants or synonymous variants may cause inherited diseases by inducing aberrant splicing. Transcript analysis is necessary to confirm the pathogenicity of such variants, but it is sometimes difficult to extract mRNA directly from patient specimens. METHODS:In this study, we conducted in vitro splicing analysis using a hybrid minigene assay and specimens from three XLAS patients with synonymous variants causing aberrant splicing, including previously reported pathogenic mutations in the same codon. The variants were c.876 A>T (p.Gly292=), c.2358 A>G (p.Pro786=), and c.3906 A>G (p.Gln1302=). RESULTS:The results from our hybrid minigene assay were sufficient to predict splicing abnormalities; c.876 A>T cause 17-bp del and 35-bp del, c.2358 A>G cause exon 29 skipping, c.3906 A>G cause exon 42 skipping, which are very likely to cause pathogenicity. Further, patients carrying c.2358 A>G exhibited a mild phenotype that may have been associated with the presence of both normal and abnormally spliced transcripts. CONCLUSION:The minigene system was shown to be a sensitive assay and a useful tool for investigating the pathogenicity of synonymous variants.
Project description:<h4>Motivation</h4>RNA-seq has been widely used to study the transcriptome. Comparing to microarray, sequencing-based RNA-seq is able to identify splicing variants and single nucleotide variants in one experiment simultaneously. This provides unique opportunity to detect variants that associated with aberrant splicing. Despite the popularity of RNA-seq, no bioinformatics tool has been developed to leverage this advantage to identify variants associated with aberrant splicing.<h4>Results</h4>We have developed PVAAS, a tool to identify single nucleotide variants that associated with aberrant alternative splicing from RNA-seq data. PVAAS works in three steps: (i) identify aberrant splicings; (ii) use user-provided variants or perform variant calling; (iii) assess the significance of association between variants and aberrant splicing events.
Project description:Next-generation sequencing (NGS) technologies have played a central role in the genetic revolution. These technologies, especially whole-exome sequencing, have become the primary tool of geneticists to identify the causative DNA variants in Mendelian disorders, including hereditary deafness. Current research estimates that 1% of all human genes have a function in hearing. To date, mutations in over 80 genes have been reported to cause nonsyndromic hearing loss (NSHL). Strikingly, more than a quarter of all known genes related to NSHL were discovered in the past 5 years via NGS technologies. In this article, we review recent developments in the usage of NGS for hereditary deafness, with an emphasis on whole-exome sequencing.
Project description:While 9% of human pathogenic variants have an established effect on pre-mRNA splicing, it is suspected that an additional 20% of otherwise classified variants also affect splicing. Aberrant splicing includes disruption of splice sites or regulatory elements, or creation or strengthening of cryptic splice sites. For the majority of variants, it is poorly understood to what extent and how these may affect splicing. We have identified cryptic splicing in an unbiased manner. Three types of cryptic splicing were analyzed in the context of pathogenic variants in the acid ?-glucosidase gene causing Pompe disease. These involved newly formed deep intronic or exonic cryptic splice sites, and a natural cryptic splice that was utilized due to weakening of a canonical splice site. Antisense oligonucleotides that targeted the identified cryptic splice sites repressed cryptic splicing at the expense of canonical splicing in all three cases, as shown by reverse-transcriptase-quantitative polymerase chain reaction analysis and by enhancement of acid ?-glucosidase enzymatic activity. This argues for a competition model for available splice sites, including intact or weakened canonical sites and natural or newly formed cryptic sites. The pipeline described here can detect cryptic splicing and correct canonical splicing using antisense oligonucleotides to restore the gene defect.
Project description:Across a variety of Mendelian disorders, ∼50-75% of patients do not receive a genetic diagnosis by exome sequencing indicating disease-causing variants in non-coding regions. Although genome sequencing in principle reveals all genetic variants, their sizeable number and poorer annotation make prioritization challenging. Here, we demonstrate the power of transcriptome sequencing to molecularly diagnose 10% (5 of 48) of mitochondriopathy patients and identify candidate genes for the remainder. We find a median of one aberrantly expressed gene, five aberrant splicing events and six mono-allelically expressed rare variants in patient-derived fibroblasts and establish disease-causing roles for each kind. Private exons often arise from cryptic splice sites providing an important clue for variant prioritization. One such event is found in the complex I assembly factor TIMMDC1 establishing a novel disease-associated gene. In conclusion, our study expands the diagnostic tools for detecting non-exonic variants and provides examples of intronic loss-of-function variants with pathological relevance.