Search Results (117)

The placenta is often described as the “window to the brain” due to its crucial role in fetal neurological development. In this study, we investigated a family where the older male offspring exhibited severe neurodevelopmental and mild motor coordination disorders. His brother displayed emotional and behavioral dysregulation along with mild motor coordination disorders. The father was asymptomatic, while the mother and daughter showed mild learning disabilities. Whole exome sequencing (WES) identified a disruptive X-linked pathogenic variant, c.1088_1089del p.Asp363GlyfsTer2, within the calpain-6 (CAPN6) gene. We have submitted this variant to the ClinVar database (RCV005234146.2). The variant was found in hemizygous condition in the affected male offspring and in heterozygous condition in both the mother and daughter. As predicted, the variant undergoes nonsense-mediated mRNA decay (NMD), preventing the translation of the CAPN6 gene into a functional protein. CAPN6 is a critical gene predominantly expressed in placental and trophoblast tissues. Although its function is not well characterized, CAPN6 is also expressed in several regions of the developing brain. Recent studies have shown that genetic variants in CAPN6 significantly influence vascular endothelial growth factor (VEGF) activity, thereby affecting angiogenesis and the blood supply essential for fetal growth and development. Although CAPN6 lacks an MIM phenotype code, we hypothesize that it might be enumerated as a novel candidate gene contributing to neurodevelopmental disorders. Functional studies are imperative to elucidate the role of CAPN6 in placental function and its potential implications for neurodevelopmental processes. This work aims to inspire further research into the role of CAPN6 in placental biology and its relevance to neurodevelopmental disorders. Full article

Background/Objectives: Familial adenomatous polyposis (FAP) is an autosomal dominant disorder caused by pathogenic variants in the adenomatous polyposis coli (APC) gene. Its attenuated form (AFAP) is characterized by fewer colorectal polyps and later onset of colorectal cancer. We aimed to characterize the molecular effects of a novel APC gene variant (NM_000038.6: c.1620_1624delinsT) identified in a patient with AFAP. Methods: A 56-year-old man with the AFAP phenotype underwent germline testing via a multigene NGS panel, which identified a novel APC gene variant (NM_000038.6: c.1620_1624delinsT). In silico analyses predicted disruption of the canonical donor splice site and a frameshift followed by the introduction of a premature stop codon. The transcriptional impact of the identified APC gene variant was investigated by mRNA analysis. Results: mRNA analysis revealed two distinct APC transcripts: the first transcript led to a truncated protein (p.Leu540PhefsTer8), and the second transcript lacked exon 12, resulting in an in-frame 26 amino acid deletion of APC protein (p.Ala517_Gly542del). The transcript lacking exon 12 was more abundant than the transcript with a premature stop codon, likely due to degradation through nonsense-mediated decay. Conclusions: The APC gene variant (NM_000038.6: c.1620_1624delinsT) exhibits a dual transcriptional effect, revealing its pathogenic role in AFAP. This study highlights the diagnostic value of combined DNA–RNA germline testing for improving the clinical classification of novel APC gene variants and their genotype–phenotype correlations in FAP. Full article

Background: Neurodevelopmental disorders (NDDs), such as autism spectrum disorder (ASD), intellectual disability (ID), and global developmental delay (GDD), frequently have underlying genetic causes. NCKAP1, a gene essential for actin cytoskeleton remodeling and neuronal development, has recently gained recognition as a promising candidate gene in NDDs. While not yet linked to a defined Mendelian disorder, damaging NCKAP1 variants have been identified in individuals with NDDs. NCKAP1 is also expressed in cardiac tissue, with emerging evidence supporting its potential involvement in cardiac development. Here, we present a case of a patient with neurodevelopmental delay and congenital heart disease (CHD) harboring a novel damaging NCKAP1 variant. Methods: Comprehensive clinical evaluations and trio exome sequencing (proband and parents) were conducted on a patient with complex cardiac and neurodevelopmental phenotypes. Results: We identified a de novo heterozygous frameshift variant in NCKAP1, NM_205842.3:c.2956_2959del p.(Ser986Hisfs*34), predicted to result in loss of function through nonsense-mediated mRNA decay. The patient’s clinical features included neonatally diagnosed and surgically repaired infradiaphragmatic total anomalous pulmonary venous return (TAPVR), intellectual disability, speech delay, and autistic traits. His NDD phenotypes and variant type align well with previously described NCKAP1-associated NDD, while the cardiac anomaly adds evidence to the gene’s expanding phenotypic spectrum. This represents the fourth reported case linking NCKAP1 variants to CHD and/or neurodevelopmental delay. Conclusions: This case strengthens the growing recognition of NCKAP1 in both neurodevelopment and cardiac formation. It highlights the importance of genetic testing for individuals with overlapping developmental and cardiac conditions. Further research is warranted to elucidate the role of NCKAP1 in cardiac development and its contribution to CHD. Full article

Background: Germline genetic variants impacting splicing are a frequent cause of disease. The clinical interpretation of such variants is challenging for many reasons including the immense complexity of splicing mechanisms. While recent advances in splicing algorithms have improved the accuracy of splice prediction, predicting the nature and abundance of aberrant splicing remains challenging. As RNA testing becomes more mainstream in the clinical diagnostic setting, the complexities of interpretation are coming to light. Methods: Data from patients undergoing concurrent DNA and RNA testing were retrospectively reviewed for unusual splicing impacts to underscore some of these complexities and serve as exemplars in how to avoid pitfalls in the interpretation of sequence variants. Results: Seven rare variants with unusual splicing impacts are presented: a variant at a consensus donor nucleotide position lacking a splice impact (NF1 c.888+2T>C); a mid-exonic missense variant creating a novel donor site and a cryptic acceptor site resulting in pseudo-intronization (BRIP1 c.727A<G p.Ile243Val); one variant creating a spliceosome switch from U12 to U2 (LZTR1 c.2232G>A p.Ala744Ala); two variants that would be expected to result in nonsense-mediated-mRNA-decay triggering splicing impacts that obviated nonsense-mediated-decay (APC c.1042C>T p.Arg348Ter and BRCA2 c.6762del; c.6816_6841+1534del); and two variants causing splicing impacts through pyrimidine tract optimization (NF1 c.5750-184_5750-178dup and ATM c.3480G>T p.Val1160Val). Conclusions: Paired DNA and RNA testing revealed unexpected splice events altering variant interpretation, expanding our knowledge of clinically important splicing mechanisms and highlighting the benefit of RNA testing. Full article

Duchenne muscular dystrophy (DMD) is a severe neuromuscular disease caused by mutations in the DMD gene, leading to muscle degeneration and shortened life expectancy. Beyond motor symptoms, DMD patients frequently exhibit brain co-morbidities, linked to loss of brain-expressed dystrophin isoforms: most frequently Dp427 and Dp140, and occasionally Dp71 and Dp40. DMD mouse models, including mdx^5cv and mdx52, replicate key aspects of the human cognitive phenotype and recapitulate the main genotypic categories of brain phenotype. However, the spatio-temporal expression of brain dystrophin in mice remains poorly defined, limiting insights into how its deficiency disrupts brain development and function. We systematically mapped RNA and protein expression of brain dystrophin isoforms (Dp427 variants, Dp140, Dp71, and Dp40) across brain regions and developmental stages in wild-type mice. Dp427 isoforms were differentially expressed in the adult brain, with Dp427c enriched in the cortex, Dp427p1/p2 in the cerebellum, and Dp427m was also detected across specific brain regions. Dp140 was expressed at lower levels than Dp427; Dp71 was the most abundant isoform in adulthood. Dp140 and Dp71 displayed dynamic developmental changes, from E15 to P60, suggesting stage-specific roles. We also analysed mdx^5cv mice lacking Dp427 and mdx52 mice lacking both Dp427 and Dp140. Both models had minimal Dp427 transcript levels, likely due to the nonsense-mediated decay, and neither expressed Dp427 protein. As expected, mdx52 mice lacked Dp140, confirming their genotypic relevance to human DMD. Our study provides the first atlas of dystrophin expression in the wild-type mouse brain, aiding understanding of the anatomical basis of behavioural and cognitive comorbidities in DMD. Full article

Background/Objectives: Hereditary hearing loss (HHL) is a genetically heterogeneous condition, involving more than 150 genes in non-syndromic cases and associated with over 400 distinct disorders in syndromic forms. Although whole-exome sequencing (WES) has markedly increased diagnostic yield, a substantial number of cases remain unsolved, often due to intronic variants that affect splicing and are difficult to interpret. This study aimed to characterize the potential impact of intronic variants predicted to alter splicing in families affected by HHL. Methods: The effect of seven intronic variants, previously identified in a diagnostic setting by WES within ADGRV1, ATP11A, GSDME, OTOF, OTOGL, and USH2A genes, was evaluated. To functionally validate these predictions, in vitro minigene splicing assays were subsequently performed. Results: All the identified variants were predicted to disrupt normal RNA splicing. The functional studies with minigene assays confirmed this observation and showed that the tested variants induced both exon skipping and activation of cryptic splice sites. In five out of seven cases, these splicing alterations caused a frameshift and introduced a premature termination codon, ultimately resulting in nonsense-mediated mRNA decay and protein degradation. Conclusions: This study expands the mutational spectrum of HL-related genes and highlights the importance of integrating in silico predictions with minigene assays. Such a combined approach is crucial for accurate interpretation of splicing variants, particularly when patient-derived RNA samples are unavailable. Full article

For 40 years, Intron Retention (IR) was dismissed as splicing noise and is now recognized as a dynamic and evolutionarily conserved mechanism of post-transcriptional gene regulation. Unlike canonical splicing, which excises all introns from pre-mRNAs, IR selectively retains intronic sequences, albeit at seemingly random places; however, current research now reveals that this process is strategic in its retention. IR influences mRNA stability, localization, and translational potential. Retained introns can lead to nonsense-mediated decay, promote nuclear retention, or give rise to novel protein isoforms that contribute to expanding proteomic and transcriptomic profiles. IR is finely regulated by splice site strength, splicing regulatory elements, chromatin structure, methylation patterns, RNA polymerase II elongation rates, and the availability of co-transcriptional splicing factors. IR plays critical roles in cell-type and tissue-specific gene expression with observed patterns, particularly during neuronal, cardiac, hematopoietic, and immune development. It also functions as a molecular switch during cellular responses to environmental and physiological stressors such as hypoxia, heat shock, and infection. Dysregulated IR is increasingly associated with cancer, neurodegeneration, aging, and immune dysfunction, where it may alter protein function, suppress tumor suppressor genes, or generate immunogenic neoepitopes. Experimental and computational tools like RNA-seq, RT-PCR, IRFinder, and IntEREst have enabled transcriptome-wide detection and validation of IR events, uncovering their widespread functional roles. This review will examine current knowledge on the function, regulation, and detection of IR, and also summarize recent advances in understanding its role in both normal and pathophysiological settings. Full article

This review highlights the emerging functional implications of nonsense-mediated mRNA decay (NMD) in human diseases, with a focus on its therapeutic potential for cardiovascular disease. NMD, conserved from yeast to humans, is involved in apoptosis, autophagy, cellular differentiation, and gene expression regulation. NMD is a highly conserved surveillance mechanism that degrades mRNAs containing premature termination codons (PTCs) located upstream of the final exon-exon junction. NMD serves to prevent the translation of aberrant mRNA and prevents the formation of defective protein products that could result in diseases. Key players in this pathway include up-frameshift proteins (UPFs), nonsense-mediated mRNA decay associated with p13K-related kinases (SMGs), and eukaryotic release factors (eRFs), among others. Dysregulation of NMD has been linked to numerous pathological conditions such as dilated cardiomyopathy, cancer, viral infections, and various neurodevelopmental and genetic disorders. This review will examine the regulatory mechanisms by which NMD regulation or dysregulation may contribute to disease mitigation or progression and its potential for cardiovascular disease therapy. We will further explore how modulating NMD could prevent the outcomes of mutations underlying genetically induced cardiovascular conditions and its applications in personalized medicine due to its role in gene regulation. While recent advances have provided valuable insights into NMD machinery and its therapeutic potential, further studies are needed to clarify the precise roles of key NMD components in cardiovascular disease prevention and treatment. Full article

The genomes of viruses in the Allexivirus genus encode the p42 protein, which is considered the hallmark of the genus. The functions of p42 have not yet been studied experimentally and cannot be predicted based on sequence similarity, as p42-related proteins are not found among known cell or viral proteins. Here, p42 of Shallot virus X (ShVX), the type allexivirus, is demonstrated to be translated via a leaky scanning mechanism on a template comprising three “triple gene block” (TGB) transport genes and the p42 gene. Sequence analysis shows that this p42 expression mechanism is conserved in the vast majority of allexiviruses. p42 binds single-stranded RNA (ssRNA) but not double-stranded RNA (dsRNA) in vitro and localizes to the cytoplasm in association with microtubules and microtubule-bound bodies. In transient expression assays, p42 exhibits weak but detectable suppression of silencing induced by ssRNA but not by dsRNA. In addition, p42 suppresses silencing in the context of virus infection. Furthermore, p42 inhibits nonsense-mediated RNA decay (NMD) induced by a long 3′-terminal untranslated region of mRNA. Taken together, these findings provide initial evidence that the ShVX TGB/p42 gene module functions as a single genomic unit in terms of protein expression, that p42 acts as a suppressor of NMD and silencing, and that it may have multiple roles, while the precise biological significance of p42 in these roles remains to be experimentally confirmed. Full article

GIGYF2 (Grb10-interacting GYF protein 2) functions as a versatile adaptor protein that regulates gene expression at various levels. At the transcriptional level, GIGYF2 facilitates VCP/p97-mediated extraction of ubiquitylated Rpb1 from stalled RNA polymerase II complexes during DNA damage response. In mRNA surveillance, GIGYF2 participates in ribosome collision-induced quality control, nonsense-mediated decay, no-go decay, and non-stop decay pathways. Furthermore, GIGYF2 interacts with key factors including 4EHP, TTP, CCR4-NOT, DDX6, ZNF598, and TNRC6A to mediate translational repression and mRNA degradation. Additionally, dysregulation of GIGYF2 has been implicated in various pathological conditions, including metabolic diseases, vascular aging, viral infections, and neurodegenerative disorders. This review summarizes the structural and functional characteristics of GIGYF2, highlighting its importance in transcriptional regulation, mRNA surveillance, translational inhibition, and mRNA degradation, while also elucidating its potential as a therapeutic target for disease treatment. Full article

The nonsense-mediated mRNA decay (NMD) is extensively involved in physiological, pathological, and stress response processes in humans and plants. However, the NMD in phytopathogenic fungi has not yet been thoroughly investigated. In this study, we identified and performed domain analysis on the core components of the NMD in ten globally widespread phytopathogenic fungi that cause significant economic losses. The core components of NMD in these fungi exhibit high similarity to their homologous genes in humans, while also possessing certain specificities. The core factors of the NMD, including the Up-frameshift factors (UPFs) and the exon junction complex (EJC), are generally conserved among phytopathogenic fungi. Notably, suppressors with morphological effects on genitalia (SMG) genes are absent in these fungi, which bears some similarity to the EJC-independent NMD degradation mechanism observed in Saccharomyces cerevisiae. Interestingly, plant pathogenic fungi contain highly homologous genes of the EJC complex, suggesting the presence of an EJC-dependent NMD degradation mechanism. In summary, our findings demonstrate that NMD are prevalent in plant pathogenic fungi, providing a research foundation for subsequent studies on NMD in their growth, development, and involvement in pathogenic processes. Full article

Adeno-associated viral (AAV) vector-mediated gene therapy has emerged as a promising alternative to liver transplantation for monogenic metabolic hepatic diseases. AAVs are non-integrative vectors that are maintained primarily as episomes in quiescent cells like adult hepatocytes. This quality, while advantageous from a safety perspective due to a decreased risk of insertional mutagenesis, becomes a disadvantage when treating dividing cells, as it inevitably leads to the loss of the therapeutic genome. This is a challenge for the treatment of hereditary liver diseases that manifest in childhood. One potential approach to avoid vector genome loss involves putting scaffold/matrix attachment regions (S/MARs) into the recombinant AAV (rAAV) genome to facilitate its replication together with the cellular genome. We found that the administration of AAVs carrying the human β-interferon S/MAR sequence to neonatal and infant mice resulted in the maintenance of higher levels of viral genomes. However, we also observed that its inclusion at the 3′ end of the mRNA negatively impacted its stability, leading to reduced mRNA and protein levels. This effect can be partially attenuated by incorporating nonsense-mediated decay (NMD)-inhibitory sequences into the S/MAR containing rAAV genome, whose introduction may aid in the development of more efficient and longer-lasting gene therapy rAAV vectors. Full article

It is known that both transcriptional and post-transcriptional mechanisms control messenger RNA (mRNA) levels. Compared to transcriptional regulations, our understanding of how post-transcriptional regulations adapt during fatty liver progression at the whole-transcriptome level is unclear. While traditional RNA-seq analysis uses only reads mapped to exons to determine gene expression, recent studies support the idea that intron-mapped reads can be reliably used to estimate gene transcription. In this study, we analyzed differential gene expression at both the exon and intron levels using two liver RNA-seq datasets from mice that were fed a high-fat diet for seven weeks (mild fatty liver) or thirty weeks (severe fatty liver). We found that the correlation between gene transcription and mature mRNA levels was much lower in mice with mild fatty liver as compared with mice with severe fatty liver. This result indicates broad post-transcriptional regulations for early fatty liver and such regulations are compromised for severe fatty liver. Specifically, gene ontology analysis revealed that genes involved in synapse organization and cell adhesion were transcriptionally upregulated, while their mature mRNAs were unaffected in mild fatty liver. Further characterization of post-transcriptionally suppressed genes in early fatty liver revealed that their mRNAs harbor a significantly longer 3′ UTR, one of the major features that may subject RNA transcripts to nonsense-mediated RNA decay (NMD). We further show that the expression of representative genes that were post-transcriptionally suppressed were upregulated in mice with a hepatocyte-specific defect of NMD. Finally, we provide data supporting a time-dependent decrease in NMD activity in the liver of a diet-induced metabolic-dysfunction-associated fatty liver disease mouse model. In summary, our study supports the conclusion that NMD is essential in preventing unwanted/harmful gene expression at the early stage of fatty liver and such a mechanism is lost due to decreased NMD activity in mice with severe fatty liver. Full article

Deleterious variations in STXBP1 are responsible for early infantile epileptic encephalopathy type 4 (EIEE4, OMIM # 612164) because of its dysfunction in the central nervous system. The clinical spectrum of the neurodevelopmental delays associated with STXBP1 aberrations is collectively defined as STXBP1 encephalopathy (STXBP1-E), the conspicuous features of which are highlighted by early-onset epileptic seizures without structural brain anomalies. A girl was first diagnosed with unexplained disorders of movement and cognition, which later developed into STXBP1-E with unexpected leukoaraiosis and late onset of seizures. Genetic screening and molecular tests alongside neurological examinations were employed to investigate the genetic etiology and establish the diagnosis. A heterozygous mutation of c.37+2dupT at the STXBP1 splice site was identified as the pathogenic cause in the affected girl. The de novo mutation (DNM) did not result in any truncated proteins but immediately triggered mRNA degradation by nonsense-mediated mRNA decay (NMD), which led to the haploinsufficiency of STXBP1. The patient showed atypical phenotypes characterized by hypomyelinating leukodystrophy, and late onset of epileptic seizures, which had never previously been delineated in STXBP1-E. These findings strongly indicated that the haploinsufficiency of STXBP1 could also exhibit divergent clinical phenotypes because of the genetic heterogeneity in the subset of encephalopathies. Full article

Eukaryotic cells possess surveillance mechanisms that detect and degrade defective transcripts. Aberrant transcripts include mRNAs with a premature termination codon (PTC), targeted by the nonsense-mediated decay (NMD) pathway, and mRNAs lacking a termination codon, targeted by the nonstop decay (NSD) pathway. The eukaryotic exosome, a ribonucleolytic complex, plays a crucial role in mRNA processing and turnover through its catalytic subunits PM/Scl100 (Rrp6 in yeast), DIS3 (Rrp44 in yeast), and DIS3L1. Additionally, eukaryotic cells have other ribonucleases, such as SMG6 and XRN1, that participate in RNA surveillance. However, the specific pathways through which ribonucleases recognize and degrade mRNAs remain elusive. In this study, we characterized the involvement of human ribonucleases, both nuclear and cytoplasmic, in the mRNA surveillance mechanisms of NMD and NSD. We performed knockdowns of SMG6, PM/Scl100, XRN1, DIS3, and DIS3L1, analyzing the resulting changes in mRNA levels of selected natural NMD targets by RT-qPCR. Additionally, we examined the levels of different human β-globin variants under the same conditions: wild-type, NMD-resistant, NMD-sensitive, and NSD-sensitive. Our results demonstrate that all the studied ribonucleases are involved in the decay of certain endogenous NMD targets. Furthermore, we observed that the ribonucleases SMG6 and DIS3 contribute to the degradation of all β-globin variants, with an exception for βNS in the former case. This is also the case for PM/Scl100, which affects all β-globin variants except the NMD-sensitive variants. In contrast, DIS3L1 and XRN1 show specificity for β-globin WT and NMD-resistant variants. These findings suggest that eukaryotic ribonucleases are target-specific rather than pathway-specific. In addition, our data suggest that ribonucleases play broader roles in mRNA surveillance and degradation mechanisms beyond just NMD and NSD. Full article