AIMS:Cardiac ageing is characterized by endothelial dysfunction and associated cardiovascular pathologies, often involving endothelial-to-mesenchymal transition (EndoMT) in cardiac endothelial cells. While the transcription factor Ets2, a member of the Ets family, is known to regulate endothelial cell survival and function, its role in EndoMT and cardiac ageing remains poorly understood. METHODS AND RESULTS:To investigate this, we utilized single-nucleus RNA sequencing (snRNA-Seq) in Ets2-super-enhancer (Ets2-SE)-deficient mice to examine the regulation of Ets2 expression across various cardiac cell types. We assessed the relationship between Ets2 expression and heart ageing and evaluated the characteristics of cardiac ageing in Ets2-SE-deficient mice. Furthermore, we generated endothelial cell-specific Ets2 knockout mice (ECKO) to investigate the role of Ets2 in EndoMT of cardiac endothelial cells both in vitro and in vivo. Our results establish a link between decreased Ets2 expression and the development of ageing-associated cardiac pathological remodelling. Through data analyses, we identified a super-enhancer (Ets2-SE) that regulates Ets2 expression in the heart. Ets2-SE-deficient mice exhibited significantly lower Ets2 expression in cardiac tissues and displayed advanced ageing phenotypes, including increased cardiac fibrosis and dysfunction, compared to wild-type controls. SnRNA-Seq analyses revealed a remarkable downregulation of Ets2 in endothelial cells, correlating with the activation of EndoMT. Furthermore, endothelial-specific deletion of Ets2 exacerbated ageing and myocardial infarction-induced cardiac fibrosis and heart dysfunction. Mechanistic studies demonstrated that silencing ETS2 in human umbilical vein endothelial cells promotes EndoMT by transcriptionally suppressing the endothelial marker gene TIE1. This transition is accompanied by endothelial cell senescence and the activation of the senescence-associated secretory phenotype, which contributes to myocardial fibrosis and cardiac ageing, partially mediated by Serpine1. These findings identify Ets2 as a critical regulator of EndoMT in the context of cardiac ageing. CONCLUSION:Our findings reveal that the Ets2 super-enhancer regulates Ets2 expression in cardiac endothelial cells, modulating heart ageing and EndoMT. Ets2's regulation of endothelial marker genes, especially TIE1, plays a pivotal role in mitigating EndoMT and preventing senescence in cardiac vascular endothelial cells, suggesting potential therapeutic targets for addressing cardiovascular ageing.

Mutations in the pre-mRNA processing factor 31 gene (PRPF31) are a common cause of autosomal dominant retinitis pigmentosa (adRP), an inherited retinopathy characterized by progressive photoreceptor degeneration and vision loss. In a large Chinese adRP pedigree, we identified a PRPF31 c.544_618del mutation that causes a drastic reduction in protein expression via haploinsufficiency. We investigated its pathogenesis using a multi-model approach and found a core pathogenic axis wherein PRPF31 deficiency downregulates polo-like kinase 4 (PLK4), relieving its inhibition on transcription factor EB (TFEB). This triggers TFEB nuclear translocation and subsequent transcriptional upregulation of autophagy/lysosomal genes, driving autophagic hyperactivation. This autophagic hyperactivation, in turn, initiates a vicious cycle with severe mitochondrial dysfunction, characterized by structural abnormalities, respiratory deficits, adenosine triphosphate deficiency, and reactive oxygen species accumulation. Our work unveils a previously unrecognized pathophysiological mechanism for PRPF31-related retinopathy, by which PRPF31 deficiency drives a pathologic cascade between autophagy and mitochondria via the PLK4-TFEB axis, and provides crucial mechanistic insight and valuable models for developing interventional strategies targeting this pathway.

Down syndrome (DS), caused by trisomy 21, has long been viewed primarily as a neurodevelopmental disorder. However, increasing evidence indicates that it is also associated with pervasive immune dysregulation, including chronic inflammation and heightened susceptibility to autoimmunity. Here, we revisit DS from the perspective of innate immunity and suggest that it shares key features with interferon-driven, autoinflammation-like conditions. Drawing on recent multi-omics studies, we outline a mechanistic framework linking chromosome 21 gene dosage to systemic immune activation. Increased expression of interferon receptors lowers the threshold for signaling and drives persistent activation of interferon-stimulated genes (ISGs). In parallel, reduced METTL3-dependent m6A modification may stabilize pro-inflammatory transcripts and enhance innate immune sensing. These changes occur alongside chromatin accessibility remodeling enriched for AP-1–associated elements, consistent with a transcriptionally primed state that amplifies inflammatory gene expression. Together, these processes form a feed-forward network involving interferon signaling, transcriptional activation, and cytokine production, providing a basis for the basal inflammatory state in DS and its high burden of immune-mediated comorbidities. This framework also highlights potential therapeutic opportunities, including JAK–STAT inhibition and cytokine-targeted approaches, which may help restore immune homeostasis and inform future translational studies.

Endogenous nitric oxide (NO) produced by nitric oxide synthases (NOSs) plays an important immunosuppressive role in the tumor microenvironment. In melanoma, NOS1 expression increases with tumor progression and correlates with tumor immune escape through the inhibition of type I interferon (IFN) signaling. However, the immune regulatory role and related mechanisms of NOS1, as well as its impacts on immune therapies such as immune checkpoint blockade (ICB) in melanoma, remain unclear. Here, we found that NOS1 expression induces IRF7 modification by S-nitrosylation at the C435 site in mice (C481 in humans), which functionally promoted tumor growth in mouse models. Mechanistically, IRF7-C435-SNO inhibited IFNβ transcription under PRR signal activation, leading to a disorder in the initiation of the type I interferon response in melanoma cells. In a melanoma mouse model, IRF7-C435-SNO decreased the infiltration and activation of CD8 + T cells in the tumor microenvironment by reducing antigen presentation processes in tumor cells and inhibiting the maturation of DC1. Clinically, high expression of NOS1 correlated with poor survival prognosis and resistance to ICB anti-tumor therapies in melanoma cases with less immune cell infiltration. Our study suggests that NOS1 expression in melanoma characterizes IFN-I signal disorders in response to innate immune stimulation through IRF7 s-nitrosylation. Targeting NOS1 signaling might be beneficial for overcoming immune therapeutically resistance, particularly in immune-cold melanoma phenotype.

Craniofacial development relies on the migration of cranial neural crest cells (CNCCs) to the first and second pharyngeal arches, followed by their differentiation into various cell types during embryogenesis. Although the CNCC migration has been well-studied, the role of the niche in relation to CNCC remains unclear. Variants in FOXI3 have been implicated in craniofacial microsomia (CFM), yet the molecular mechanisms remain unexplored. FOXI3 is expressed in the ectoderm and auricle epidermis, but not in CNCCs or cartilage. Deletion of Foxi3 in the mouse CNCCs did not disrupt mandible and auricular development, further confirming that FOXI3 does not directly regulate CNCCs. However, Foxi3 deficiency in the ectoderm reduced the production of chondrogenesis-related cytokines derived from ectodermal cells, such as TGF-β1. This impairment affected CNCC proliferation through cell communication, subsequently altering the development of the mandible and auricle. These results emphasize the critical role of FOXI3 in establishing the microenvironment supporting CNCC function. Furthermore, FOXI3 directly regulates target genes associated with translation, thereby orchestrating cytokine production in epidermal cells. The validation using auricle sample from a CFM patient carrying FOXI3 mutation further supports our findings. These insights highlight the function of FOXI3 in creating the niche necessary for CNCC development and provide a basis for understanding the molecular mechanisms driving CFM pathogenesis.

The iron regulatory protein IREB2 (Iron Responsive Element Binding Protein 2) plays a crucial role in maintaining cellular iron homeostasis through the posttranscriptional regulation of genes involved in iron metabolism. Mutations in the IREB2 gene have been linked to NDCAMA (OMIM#618451), a rare genetic neurological disorder characterized by early-onset neurodegeneration, choreoathetoid movements, and microcytic anemia. However, the absence of an IREB2-mutated animal model has left the underlying pathogenic mechanisms poorly understood. To investigate this, we establish a CRISPR-Cas9-mediated Ireb2 D826V/D826V mouse model, which carries the c.2477A>T (p.D826V) pathogenic variant in IREB2 identified in a Chinese pedigree with NDCAMA. Behavioral studies, including the Morris water maze (MWM), open field test (OFT), and Y-maze, reveal significant neurobehavioral deficits, such as impaired spatial learning and memory and reduced motor activity, in Ireb2 D826V/D826V mice. Furthermore, we observe increased microglial activation and decreased dendritic spine density in the hippocampus, along with impaired long-term potentiation (LTP) and elevated paired-pulse facilitation (PPF), indicating synaptic dysfunction. Mechanistically, Ireb2 D826V/D826V mice present reduced Ireb2 protein levels, dysregulated iron metabolism, and an altered expression profile associated with neurological function. This study elucidates the molecular mechanisms underlying NDCAMA and establishes Ireb2 D826V/D826V mice as a model for iron metabolism-driven neurodegeneration. This finding links the instability of IREB2 to synaptic failure and neuroinflammation, highlighting potential therapeutic implications for neurodegenerative diseases.

Dilated cardiomyopathy (DCM)-associated heart failure (HF) presents a significant clinical challenge, underlying epigenetic mechanisms remaining poorly understood. This study aims to investigate the interplay between DNA methylation and gene expression in the hearts of patients with DCM-associated HF (DCM-HF). Atrial tissues were collected from five healthy donors and five heart transplant recipients suffering from heart failure due to DCM. We conducted RNA-sequencing (RNA-seq) to analyze mRNA expression profiles and performed whole-genome bisulfite sequencing (WGBS) to evaluate DNA methylation levels. Correlation analyses between RNA-seq and WGBS data were executed by integrating differentially expressed genes (DEGs) with genes associated with differentially methylated regions (DMRs) located in the promoter regions. The RNA-seq analysis identified a total of 681 DEGs, comprising 406 significantly downregulated genes and 275 upregulated genes in DCM-HF tissues, which were enriched in pathways related to cardiomyopathy. WGBS revealed 16,158 hypomethylated and 6,857 hypermethylated differentially methylated regions (DMRs), with 3,185 of these located in promoter regions. The integration of promoter-hypomethylated and hypermethylated DMRs-related genes (DMGs) with DEGs resulted in the identification of 46 hub genes associated with cardiac development and function. Protein–protein interaction and disease association analyses highlighted five key genes—NPPA, NPPB, ACTN2, NEBL, and MYO18B-that exhibited promoter hypomethylation and increased expression, potentially linked to the activity of transcription factors such as HIF1A and KLF4. These findings suggest that the epigenetic dysregulation of cardiac stress-response and structural genes contributes to the pathogenesis of DCM-HF. Furthermore, the detection of promoter methylation levels in these loci may offer new opportunities for developing diagnostic tools and therapeutic strategies for DCM-HF management.

Acute posterior multifocal placoid pigment epitheliopathy (APMPPE) is an exceptionally rare inflammatory disorder affecting choroid and retinal pigment epithelial (RPE) cells. Although recent studies suggest an immune-driven nature, the underlying etiology of APMPPE remains elusive. In this study, we conducted a comprehensive investigation on the peripheral blood mononuclear cells (PBMCs) profile of an APMPPE patient using single-cell RNA sequencing. Our analysis revealed striking transcriptional alterations in monocytes within the PBMCs, identifying five distinct subpopulations: S100A12, CD16, pro-inflammatory, megakaryocyte-like, and NK-like monocyte subsets. Employing pseudotime inference, we observed a shift in APMPPE monocytes towards differentiation into inflammation-associated pro-inflammatory monocytes and a CD16 monocyte trajectory. Furthermore, we identified IFITM3 as a key player in the immune response driving the pathogenesis of APMPPE. Notably, two disease-relevant subgroups of monocytes, pro-inflammatory and CD16 monocytes, were implicated in APMPPE. CD16 monocytes, in particular, were involved in melanogenesis, suggesting that the abnormal expression of melanin in monocytes might result from autoimmune responses against pigment-enriched RPE cells. This study provided a comprehensive view of immune landscape in APMPPE, shedding light on the previously unrecognized contributions of pro-inflammatory and CD16 monocytes to this autoimmune condition.

Wang and colleagues linked SARS-CoV-2 infection during early pregnancy to situs inversus, a rare developmental anomaly of organ placement. However, the absence of genetic testing data raises concerns regarding the reliability of their conclusions, particularly since a similar association was not observed in Scandinavian countries. In this study, we summarize the cases of situs inversus diagnosed during the COVID-19 pandemic in Henan, China, which indicates a significant increase in the incidence of this condition. Among the 34 cases examined, 24 did not reveal any potential pathogenic variants through genetic testing. Our findings suggest a correlation between SARS-CoV-2 infection and the development of situs inversus.

Congenital ptosis, a genetic disorder involving levator palpebrae muscle dysfunction, is often associated with congenital myopathy. The genetic causes of this condition remain poorly understood. In this study, we identified FOXK2 mutations in five pedigrees with congenital myopathy and ptosis through whole exome sequencing and Sanger sequencing. Zebrafish with foxk2 deficiency exhibited underdeveloped skeletal muscles and reduced mobility, while mice with Foxk2 deletion in skeletal muscle stem cells (MuSCs) showed generalized skeletal muscle abnormalities. Further analysis revealed that FOXK2 deficiency impaired myogenic differentiation in C2C12 cells and disrupted mitochondrial homeostasis in both mouse MuSCs and C2C12 cells. Rescue experiments confirmed the loss-of-function effects of FOXK2 mutation. Coenzyme Q10 treatment improved mitochondrial function and alleviated skeletal muscle development defects in Foxk2 -deficient mice. Preliminary omics analysis suggested FOXK2 directly regulates the expression of mitochondrial function-related genes by modulating chromatin accessibility at its binding sites. Our study identifies FOXK2 as a novel pathogenic gene for congenital myopathy with ptosis and highlights its essential role in skeletal muscle development and mitochondrial homeostasis, offering insights for potential diagnostics and therapies.

T cell receptor (TCR) diversity, essential for the recognition of a wide array of antigens, is generated through V(D)J recombination. The Tcra and Tcrd genes reside within a shared genomic locus, with Tcrd rearrangement occurring first in the double-negative (DN) stage during thymocyte development. Elucidating the regulatory mechanisms governing Tcrd rearrangement is therefore crucial for understanding the developmental coordination of both Tcrd and Tcra rearrangements. Chromatin architecture, orchestrated by CTCF-cohesin complexes and their binding sites, plays a fundamental role in regulating V(D)J recombination of antigen receptor genes. In this study, we report that EACBE, a CTCF binding element (CBE) located downstream of the Tcra-Tcrd locus, regulates Tcrd rearrangement. EACBE promotes the usage of proximal Vδ gene segments by facilitating spatial proximity between the Tcrd recombination centre and these Vδ elements. Notably, EACBE counteracts the insulating effects of INTs, two CBEs that demarcate the proximal V region from the Dδ-Jδ-Cδ cluster, thereby enabling effective chromatin extrusion. Furthermore, EACBE indirectly shapes the Tcra repertoire through its influence on Tcrd rearrangement. These findings reveal a novel regulatory axis involving special chromatin configuration and highlight distinct roles for specific CTCF binding sites in modulating antigen receptor gene assembly.

[This corrects the article DOI: 10.3389/fmed.2025.1514504.].

Background and objective:Increased nuchal translucency (NT) thickness measured at 11-14 weeks of gestation in fetuses has been linked to adverse pregnancy outcomes. This study aimed to evaluate pregnancy outcomes in fetuses with NT ≥3.0 mm. Methods:This retrospective analysis included 4,200 singleton pregnancies diagnosed with increased NT thickness (≥3.0 mm) through first-trimester ultrasound screening across 76 hospitals in Henan Province from 2017 to 2021. Follow-up on pregnancy outcomes was completed through telephone interviews and electronic medical records. Results:Among the 4,200 pregnancies with NT ≥3.0 mm, adverse pregnancy outcomes were observed in 31.5% of the fetuses. These outcomes included elective termination of pregnancy (TOP), spontaneous abortion (SA), threatened abortion (TA), and live birth with malformations. A total of 547 fetuses underwent further examination through karyotype analysis after genetic counseling, revealing that 10.2% were aneuploid, primarily due to Trisomy 21 (7.1%). Conclusion:The incidence of increased NT in our study was 0.49%, which was associated with chromosomal abnormalities and developmental disorders, leading to an increased risk of adverse pregnancy outcomes. Abnormal ultrasound soft markers, along with NT > 4 mm, may further elevate the risk of adverse pregnancy outcomes. These findings should be taken seriously in the context of further prenatal diagnosis for fetuses with increased NT.

Visceral heterotaxy is a congenital malformation characterized by the abnormal arrangement of left–right axis of visceral organs. To date, several genes implicated in the regulation of laterality patterning have been identified. Notably, CFAP53, also referred to as CCDC11, is involved in the regulation of ciliary motility, and mutations in this gene have been linked to a rare condition of heterotaxy. In this study, whole-exome sequencing (WES) was utilized to analyze the genetic causes of a fetus in a Chinese family, presenting with situs inversus totalis. In silico predictions and functional studies were performed to evaluate the pathogenicity of the identified candidate gene variants. WES revealed two novel compound heterozygous mutations, c.777G > T and c.1013A > T, in the CFAP53 gene. Minigene experiments demonstrated that c.777G > T may result in splicing aberrations, thus leading to the production of truncated CFAP53 proteins. Additionally, in silico analyses indicate that c.1013A > T could disrupt the interaction between CFAP53 and its target protein, TTC25. We report the second documented case of fetus with situs inversus totalis due to biallelic loss-of-function variants in CFAP53. According to literature review, our findings provide a basis for the prenatal diagnosis and genetic counseling of CFAP53 mutation-associated visceral heterotaxy.

SMARCB1 encodes a core subunit of the SWI/SNF chromatin remodeling complex, which plays a crucial role in the regulation of gene expression. Germline mutations in the SMARCB1 gene have been linked to early childhood Coffin-Siris syndrome type 3 (CSS3), a rare congenital malformation syndrome characterized by severe developmental delay and intellectual disability. In this study, we report a family of two adult CSS3 patients with a novel missense SMARCB1 mutation (c.1091A>C, p.Lys364Thr) identified through whole-exome sequencing (WES). Both patients exhibit selective difficulties in verbal learning and experience language delays. Additionally, the development of meningioma is confirmed in one of the patients. Mechanistic studies suggest that this missense mutation may abnormally activate the MAPK signaling pathway, which is implicated in the pathogenesis of tumor progression and neurodevelopmental disorders. This is the first reported case of a germline mutation in the SMARCB1 gene associated with both CSS3 and meningioma, thereby expanding the phenotypic spectrum of SMARCB1-related disorders.

Background KIDINS220 encodes a transmembrane scaffold protein, kinase D-interacting substrate of 220 kDa, that regulates neurotrophin signaling. Variants in KIDINS220 have been linked to spastic paraplegia, intellectual disability, nystagmus, and obesity (SINO) syndrome or prenatal fatal cerebral ventriculomegaly and arthrogryposis (VENARG). This study aimed to investigate the genotype-phenotype correlation of pathogenic KIDINS220 variants. Methods We performed whole-exome sequencing on a patient with SINO syndrome and epilepsy. Identified pathogenic variants were confirmed using Sanger sequencing and evaluated with in silico tools. A comprehensive literature review was conducted to analyze the genetic and phenotypic data of both the newly diagnosed patient and previously reported cases with KIDINS220 variants. Results We identified novel compound heterozygous variants in KIDINS220, c.1556C>T (p.Thr519Met) and c.2374C>T (p.Arg792*), in the patient. Our analysis revealed that biallelic loss-of-function variants in KIDINS220 are associated with VENARG or autosomal recessive SINO (AR-SINO), whereas carboxy-terminal truncated variants that escape nonsense-mediated mRNA decay and lack amino acid residues 1507-1529 are linked to autosomal dominant SINO (AD-SINO). Patients with AR-SINO exhibit more severe clinical features compared to those with AD-SINO. Conclusions Our study expands the spectrum of KIDINS220 variants associated with AR-SINO and provides a valuable genotype-phenotype correlation for pathogenic KIDINS220 variants.

Abnormal cardiac development has been observed in individuals with Cornelia de Lange syndrome (CdLS) due to mutations in genes encoding members of the cohesin complex. However, the precise role of cohesin in heart development remains elusive. In this study, we aimed to elucidate the indispensable role of SMC3, a component of the cohesin complex, in cardiac development and its underlying mechanism. Our investigation revealed that CdLS patients with SMC3 mutations have high rates of congenital heart disease (CHD). We utilized heart-specific Smc3-knockout (SMC3-cKO) mice, which exhibit varying degrees of outflow tract (OFT) abnormalities, to further explore this relationship. Additionally, we identified 16 rare SMC3 variants with potential pathogenicity in individuals with isolated CHD. By employing single-nucleus RNA sequencing and chromosome conformation capture high-throughput genome-wide translocation sequencing, we revealed that Smc3 deletion downregulates the expression of key genes, including Ets2, in OFT cardiac muscle cells by specifically decreasing interactions between super-enhancers (SEs) and promoters. Notably, Ets2-SE-null mice also exhibit delayed OFT development in the heart. Our research revealed a novel role for SMC3 in heart development via the regulation of SE-associated genes, suggesting its potential relevance as a CHD-related gene and providing crucial insights into the molecular basis of cardiac development. Understanding heart development is vital as defects in this process are a major cause of birth abnormalities. This study focuses on a protein, SMC3, and its role in heart development. Experiments were conducted on mice genetically altered to lack SMC3 in heart cells. Researchers found that mice without SMC3 had various heart defects, like those seen in humans with congenital heart disease. They also found mutations in the SMC3 gene in patients with congenital heart disease, suggesting a link between SMC3 and heart development in humans. The findings reveal that SMC3 plays a crucial role in heart development, with its absence leading to significant heart defects in mice. These results suggest a potential genetic cause for some forms of congenital heart disease in humans.This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.Introduction

Down syndrome (DS), caused by an additional chromosome 21, has a high risk of congenital heart defects (CHD), one of the primary causes of mortality in DS newborns. To elucidate the pathogenetic mechanisms underlying this condition, we explored the role of RNA m6A methylation, regulated by METTL3, in DS cardiac development and its impact on the expression of SH3BGR, a gene located at Down syndrome congenital heart disease (DS-CHD) minimal region. We analyzed DS fetal cardiac tissues to assess RNA m6A methylation levels and identify potential contributors. RNA sequencing was performed to detect differentially expressed genes in the same tissues. To further understand METTL3’s function in heart development, we inactivated Mettl3 in the developing mouse heart to mimic the significantly reduced METTL3 observed in DS cardiac development. Additionally, human cardiomyocyte AC16 cells were used to investigate the molecular mechanism by which METTL3 regulates SH3BGR expression. Apoptosis was analyzed to evaluate METTL3’s effect on heart development through SH3BGR regulation. Reduced m6A modification and decreased METTL3 expression were observed in human DS fetal hearts, along with a significant increase of SH3BGR expression. METTL3, through m6A modification, was found to regulate SH3BGR expression, by influencing mRNA stability. METTL3-deficient mouse embryos exhibited heart malformation with increased apoptosis, emphasizing its role in heart development. In DS hearts, METTL3 downregulation and SH3BGR upregulation, potentially orchestrated by abnormal m6A modification, contribute to gene dysregulation and apoptosis. This study reveals novel insights into DS cardiac pathology, highlighting the intricate role of METTL3 in DS congenital heart defects and presenting the m6A modification of SH3BGR as a potential therapeutic target.

Abstract Background Cellular iron metabolism is essential for maintaining various biological processes in organisms, and this is influenced by the function of iron-responsive element-binding protein 2 (IRP2), encoded by the IREB2 gene. Since 2019, three cases of a genetic neurodegenerative syndrome resulting from compound heterozygous mutations in IREB2 have been documented, highlighting the crucial role of IRP2 in regulating iron metabolism homeostasis. This study aims to investigate the molecular basis in a single proband born to non-consanguineous healthy parents, presenting with severe psychomotor developmental abnormalities and microcytic anemia. Methods Trio-whole exome sequencing (WES) was applied to identify the disease-causing gene in an 8-month-old male patient from China. In silico tools were used to predict the pathogenicity of the identified variants, and in vitro functional studies were performed to evaluate the molecular mechanism. Results WES identified novel biallelic variants, c.1111 A > G (P.Ile371Val) and c.2477 A > T (P.Asp826Val), in the IREB2 gene, which encodes the iron metabolism-related protein, IRP2. Functional studies revealed that c.2477 A > T resulted in a significant degradation of IRP2, which led to the misregulation of intracellular ferric iron. Conclusions We report the identification of the first functional domain associated with the degradation of IRP2. The biallelic variants that affect protein degradation likely underlie the pathogenesis of the IRP2-related neurodegenerative disorder. Moreover, the use of proteasome inhibitors can potentially restore the expression of IRP2, highlighting a promising therapeutic target for patients with IRP2deficiency.

Spondyloepiphyseal dysplasia tarda (SEDT) is a condition involving late-onset, X-linked recessive skeletal dysplasia caused by mutations in the TRAPPC2 gene. In this paper, we identified a novel nonsense variant in a SEDT pedigree and analyzed the function of the variant in an attempt to explain the new pathogenesis of the TRAPPC2 protein in SEDT. Briefly, DNA and RNA samples from the peripheral blood of SEDT individuals were prepared. The causative variant in the Chinese SEDT family was identified by clinic whole-exome sequencing analysis. Then, we observed the mRNA expression of TRAPPC2 in patients and the mutant TRAPPC2 level in vitro and analyzed the protein stability and subcellular distribution by cell fluorescence and Western blotting. We also investigated the effect of TRAPPC2 knockdown on the expression and secretion of COL2A1 in SW1353 cells or primary human chondrocytes. Herein, we found a nonsense variant, c.91A>T, of the TRAPPC2 gene in the pedigree. TRAPPC2 mRNA expression levels were significantly decreased in the available peripheral blood cell samples of two affected patients. An in vitro study showed that the mutant plasmid exhibited significantly lower mRNA and protein of TRAPPC2, and the mutant protein changed its membrane distribution. TRAPPC2 knockdown resulted in decreased COL2A1 expression and collagen II secretions. Our data indicate that the novel nonsense variant, c.91A>T, of the TRAPPC2 gene is the cause of SEDT in this pedigree. The variant results in a lowered expression of TRAPPC2 and then affects the COL2A1 expression and collagen II secretions, which may explain the mechanism of loss of function of the variant.