DYNC2H1 splicing variants causing severe prenatal short-rib polydactyly syndrome and postnatal orofaciodigital syndrome.

The DYNC2H1 gene has been associated with short-rib polydactyly syndrome (SRPS), among other skeletal ciliopathies. Two cases are presented of distinctive phenotypes resulting from splicing variants in DYNC2H1. The first is a 14-week-old fetus with enlarged nuchal translucency, oral hamartoma, malformed uvula, bifid epiglottis, short ribs, micromelia, long bone agenesis, polysyndactyly, heart defect, pancreatic cysts, multicystic dysplastic kidney, megabladder and trident acetabulum. A ciliopathies NGS panel revealed two compound heterozygous variants in DYNC2H1: c.7840-18T>G r.7841_7964del p.Gly2614Aspfs*5 and c.11070G>A r.11044_11116del p.Ile3682Aspfs*2. Both variants were initially classified as variants of uncertain significance but were reclassified as likely pathogenic after PCR-based RNA testing. The second is an 11-year-old overweight male with multiple accessory oral frenula, median cleft lip and alveolar ridge, polysyndactyly, brachydactyly, normal rib length, and hypogonadism. Exome sequencing revealed two compound heterozygous variants in DYNC2H1: c.6315del p.(Thr2106Glnfs*7), classified as likely pathogenic, and c.3303-16A>G p.(?), classified as a variant of uncertain significance. PCR-based RNA testing suggested that c.3303-16A>G induces an in-frame deletion: r.3303_3458del p.Asp1102_Arg1153del, although the normal transcript is still produced. These results are consistent with both SRPS type I/III in the first case and orofaciodigital syndrome in the second, an unprecedented description. This work thus improves the clinical and molecular knowledge of the phenotypes associated with splicing variants in the DYNC2H1 gene.

A novel MMUT splicing variant causing mild methylmalonic acidemia phenotype.

Objectives: Methylmalonic acidemia (MMA) is a rare inborn genetic disorder that is characterized by increased levels of methylmalonic acid in blood plasma and urine. Isolated methylmalonic acidemia is one of the most common types of MMA and is caused by mutations in the gene encoding methyl-malonyl coenzyme A mutase (MMUT). In this study, we investigated the possible mechanisms underlying the symptoms of isolated MMA in a patient by molecular analysis. Methods: PCR amplification and Sanger sequencing analysis was performed to identify variants in the MMUT gene in the proband and his family. Furthermore, minigene constructs were generated to validate the splicing defects in the MMUT gene variant identified in the proband. Results: The 3-year-old patient was admitted to the hospital with symptoms of MMA, including fever, convulsions, and vomiting. He showed metabolic acidosis, high levels of methylmalonic acid in blood and urine, and normal blood homocysteine levels. Genetic analysis demonstrated that the patient was a compound heterozygous carrier of two variants in the MMUT gene: a missense c.278G > A variant that has already been reported in a patient with the severe mut° phenotype; and a novel splice site variant c.2125-2A > G. RT-PCR analysis showed that, while the novel variant clearly alters splicing, a minor amount of a full-length transcript is generated, suggesting that a wild-type protein may be produced although at a lower quantitative level. The patient's condition improved after treatment with vitamin B12. Serious complications were not reported during follow-up at age 5. Conclusions: We identified a novel splice site variant that partially disrupts normal splicing of the MMUT pre-mRNA. Production of a reduced amount of full-length transcript is responsible for the mild clinical phenotype observed in this patient. Functional studies have proven useful in exploring the genotype-phenotype association and in providing guidance for the genetic diagnosis of MMA.

Predicting the effect of variants on splicing using Convolutional Neural Networks.

Mutations that cause an error in the splicing of a messenger RNA (mRNA) can lead to diseases in humans. Various computational models have been developed to recognize the sequence pattern of the splice sites. In recent studies, Convolutional Neural Network (CNN) architectures were shown to outperform other existing models in predicting the splice sites. However, an insufficient effort has been put into extending the CNN model to predict the effect of the genomic variants on the splicing of mRNAs. This study proposes a framework to elaborate on the utility of CNNs to assess the effect of splice variants on the identification of potential disease-causing variants that disrupt the RNA splicing process. Five models, including three CNN-based and two non-CNN machine learning based, were trained and compared using two existing splice site datasets, Genome Wide Human splice sites (GWH) and a dataset provided at the Deep Learning and Artificial Intelligence winter school 2018 (DLAI). The donor sites were also used to test on the HSplice tool to evaluate the predictive models. To improve the effectiveness of predictive models, two datasets were combined. The CNN model with four convolutional layers showed the best splice site prediction performance with an AUPRC of 93.4% and 88.8% for donor and acceptor sites, respectively. The effects of variants on splicing were estimated by applying the best model on variant data from the ClinVar database. Based on the estimation, the framework could effectively differentiate pathogenic variants from the benign variants (p = 5.9 × 10-7). These promising results support that the proposed framework could be applied in future genetic studies to identify disease causing loci involving the splicing mechanism. The datasets and Python scripts used in this study are available on the GitHub repository at https://github.com/smiile8888/rna-splice-sites-recognition.

Pan-cancer repository of validated natural and cryptic mRNA splicing mutations.

We present a major public resource of mRNA splicing mutations validated according to multiple lines of evidence of abnormal gene expression. Likely mutations present in all tumor types reported in the Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium (ICGC) were identified based on the comparative strengths of splice sites in tumor versus normal genomes, and then validated by respectively comparing counts of splice junction spanning and abundance of transcript reads in RNA-Seq data from matched tissues and tumors lacking these mutations. The comprehensive resource features 341,486 of these validated mutations, the majority of which (69.9%) are not present in the Single Nucleotide Polymorphism Database (dbSNP 150). There are 131,347 unique mutations which weaken or abolish natural splice sites, and 222,071 mutations which strengthen cryptic splice sites (11,932 affect both simultaneously). 28,812 novel or rare flagged variants (with <1% population frequency in dbSNP) were observed in multiple tumor tissue types. An algorithm was developed to classify variants into splicing molecular phenotypes that integrates germline heterozygosity, degree of information change and impact on expression. The classification thresholds were calibrated against the ClinVar clinical database phenotypic assignments. Variants are partitioned into allele-specific alternative splicing, likely aberrant and aberrant splicing phenotypes. Single variants or chromosome ranges can be queried using a Global Alliance for Genomics and Health (GA4GH)-compliant, web-based Beacon "Validated Splicing Mutations" either separately or in aggregate alongside other Beacons through the public Beacon Network, as well as through our website. The website provides additional information, such as a visual representation of supporting RNAseq results, gene expression in the corresponding normal tissues, and splicing molecular phenotypes.

Unusual splice site mutations disrupt FANCA exon 8 definition.

The pathological role of mutations that affect not conserved splicing regulatory sequences can be difficult to determine. In a patient with Fanconi anemia, we identified two unpredictable splicing mutations that act on either sides of FANCA exon 8. In patients-derived cells and in minigene splicing assay, we showed that both an apparently benign intronic c.710-5T>C transition and the nonsense c.790C>T substitution induce almost complete exon 8 skipping. Site-directed mutagenesis experiments indicated that the c.710-5T>C transition affects a polypyrimidine tract where most of the thymidines cannot be compensated by cytidines. The c.790C>T mutation located in position -3 relative to the donor site induce exon 8 skipping in an NMD-independent manner and complementation experiments with modified U1 snRNAs showed that U1 snRNP is only partially involved in the splicing defect. Our results highlight the importance of performing splicing functional assay for correct identification of disease-causing mechanism of genomic variants and provide mechanistic insights on how these two FANCA mutations affect exon 8 definition.

A synonymous (c.3390C>T) or a splice-site (c.3380-2A>G) mutation causes exon 26 skipping in four patients with von Willebrand disease (2A/IIE).

INTRODUCTION: We characterized four unrelated patients with von Willebrand disease type 2A/IIE, sharing the same von Willebrand factor (VWF) in-frame deletion (p.[P1127_G1180delinsR];[=]) resulting from exon 26 skipping (Δ26). OBJECTIVES: To identify the VWF mutations and how they caused the mRNA splicing alteration, to evaluate the deletion by in vitro expression studies, and to assess whether or not the heterogeneity of the patients' phenotype might be related to a different degree of expression of the deleted subunit in patient plasma VWF. METHODS: Sequence analysis was performed with patient genomic DNA and platelet mRNA. Semiquantitative RT-PCR was also carried out to compare the expression of the wild-type (WT) and Δ26 alleles in the four patients. In silico analysis was performed with prediction splicing programs. Expression studies were performed to evaluate mutant recombinant VWF (rVWF) (Δ26 and Δ26/WT) as compared with WT rVWF. RESULTS: Three patients shared the synonymous single-nucleotide substitution (SSS) c.[3390C>T];[=], whereas the novel mutation c.[3380-2A>G];[=] was present in the fourth patient. Semiquantitative RT-PCR of platelet mRNA revealed a different ratio of the WT and Δ26 alleles in the patients, consistent with the different VWF:FVIIIB values present in patient plasma. Expression studies confirmed reduced VWF-FVIII binding of rVWF-Δ26/WT. CONCLUSIONS: SSS can induce alternative splicing, and those like c.3390C>T, which impact on the poorly conserved splicing regulatory elements, are difficult to predict, so that their role can be evaluated only by mRNA analysis. Moreover, these mutations seem to have different effects on the efficiency of alternative splicing, producing heterogeneous VWF variants among the four patients.