Search Results (35)

Primary dystrophin deficiency, caused by X-chromosome mutations within the DMD gene, encompasses a continuous clinical spectrum of neurological, muscular, and cardiac disorders known as dystrophinopathies that exhibit profound phenotypic variability driven by specific mutation profiles and epigenetic factors. This comprehensive review analyzes the clinical and molecular characteristics of seven primary classifications: Duchenne muscular dystrophy (DMD), a severe childhood myopathy caused by a complete absence of the protein that leads to loss of ambulation and fatal cardiorespiratory failure in youth; Becker muscular dystrophy (BMD), a milder variant with partial protein deficiency that preserves walking capabilities into adulthood and prolongs life expectancy; pseudometabolic dystrophinopathic syndrome, featuring exercise intolerance, cramps, and recurrent rhabdomyolysis that mimics metabolic diseases; asymptomatic dystrophinopathy, representing the mild end of the spectrum identified incidentally through chronically elevated creatine kinase levels; brain dystrophin-related syndrome, where the disruption of distal isoforms like Dp140 and Dp71 results in neurodevelopmental and neuropsychiatric comorbidities such as ADHD, autism, and intellectual disability; X-linked dilated cardiomyopathy (XLDCM), a cardiac-selective condition causing severe heart failure and arrhythmias while sparing skeletal muscle function; and female dystrophin-related syndrome, distinguishing between familial carriers—who can manifest symptoms due to skewed X-chromosome inactivation—and rare sporadic females who develop an exceptional, severe, Duchenne-like phenotype due to cytogenetic accidents such as Turner syndrome or chromosomal translocations. Ultimately, advancements in molecular testing (NGS and WGS) have significantly optimized diagnostic precision, proving essential for implementing early cardioprotective care, accurate genetic counseling, and the development of future tissue-specific targeted gene therapies. The present study also discusses the psychosocial impact that the disease has on patients. Full article

Turner syndrome (TS), a disorder caused by the complete or partial absence of an X chromosome, exhibits significant clinical variability that cannot be fully explained by chromosomal anomalies alone. This narrative review highlights the crucial role of epigenetic mechanisms, particularly X-chromosome inactivation (XCI), in shaping the TS phenotype. The haploinsufficiency of genes that normally escape XCI is a primary driver of TS features. The specific epigenetic consequences depend on the chromosomal anomaly. In complete monosomy (45,X), the absence of escape-mediated dosage compensation genes from a second X chromosome amplifies haploinsufficiency across X-linked escape genes. Isochromosome Xq (i(Xq)) variants involve the loss of the short arm (Xp) and duplication of the long arm (Xq), creating a dual dosage imbalance with extreme XCI skewing. Carriers of i(Xq) also have a heightened risk for autoimmune disorders compared to those with 45,X TS. For ring-X chromosomes (r(X)), which are mitotically unstable, the functional status of the XIST gene is critical. If the ring is XIST-negative, it remains transcriptionally active, resulting in functional disomy and a more severe phenotype with pronounced neurodevelopmental and craniofacial features. Ultimately, the clinical heterogeneity in TS arises from a complex interplay of the specific chromosomal structure, tissue-specific mosaicism, XIST function, and variable escape from XCI, defining TS as a disorder of epigenetic and gene-regulatory imbalance. However, future research requires a better understanding of the complex mechanism of X-chromosome inactivation. Full article

NKAP (NF-kappa-B-activating protein) is a ubiquitously expressed nuclear protein involved in multiple biological processes. Males with missense NKAP mutations have been reported to present with marfanoid features and behavioral and musculoskeletal abnormalities. We have previously reported that a disruptive NKAP mutation resulted in extremely skewed X chromosome inactivation (XCI), leading to phenotypic manifestation of hemophilia A (HA) in a HA carrier. In this study, with the aim of exploring the phenotypic manifestations of deleterious NKAP mutations in males, as well as their involvement in the mechanism of XCI regulation in females, we generated NKAP mutant mice using CRISPR/Cas9 technology. Gait analysis studies conducted in male mice hemizygous for mutant NKAP by the CatWalk XT system revealed significant alterations in gait parameters, consistent with hypotonia reported in human mutant NKAP patients. By breeding mutant NKAP mice with HA mice, we generated a double heterozygous mutant NKAP/HA mouse model, i.e., female mice carrying mutant NKAP with a WT F8 copy on one X chromosome, and WT NKAP with a mutant F8 copy on the other X chromosome. XCI pattern analysis using methylation-sensitive restriction enzymes demonstrated that mutant NKAP/HA females exhibited significant XCI skewing of the X chromosome bearing the mutant NKAP copy. Furthermore, these females exhibited significantly reduced F8 mRNA levels and FVIII (factor VIII) antigen levels, as demonstrated by quantitative RT-PCR and ELISA, respectively. Murine embryonic fibroblasts (MEFs) derived from a hemizygous mutant NKAP embryo exhibited markedly reduced proliferation rate and increased senescence compared to WT NKAP MEFs, suggesting that XCI skewing induced by mutant NKAP results from secondary selection against cells with an active X chromosome bearing the mutant NKAP copy. Full article

Background: ALG13-CDG is an X-linked N-linked glycosylation disorder caused by pathogenic variants in the glycosyltransferase ALG13, leading to severe neurological manifestations. Despite the clear CNS involvement, the impact of ALG13 dysfunction on human brain glycosylation and neurodevelopment remains unknown. We hypothesize that ALG13-CDG causes brain-specific hypoglycosylation that disrupts neurodevelopmental pathways and contributes directly to cortical network dysfunction. Methods: We generated iPSC-derived human cortical organoids (hCOs) from individuals with ALG13-CDG to define the impact of hypoglycosylation on cortical development and function. Electrophysiological activity was assessed using MEA recordings and integrated with multiomic profiling, including scRNA-seq, proteomics, glycoproteomics, N-glycan imaging, lipidomics, and metabolomics. X-inactivation status was evaluated in both iPSCs and hCOs. Results: ALG13-CDG hCOs showed reduced glycosylation of proteins involved in ECM organization, neuronal migration, lipid metabolism, calcium homeostasis, and neuronal excitability. These pathway disruptions were supported by proteomic and scRNA-seq data and included altered intercellular communication. Trajectory analyses revealed mistimed neuronal maturation with early inhibitory and delayed excitatory development, indicating an E/I imbalance. MEA recordings demonstrated early network hypoactivity with reduced firing rates, immature burst structure, and shortened axonal projections, while transcriptomic and proteomic signatures suggested emerging hyperexcitability. Altered lipid and GlcNAc metabolism, along with skewed X-inactivation, were also observed. Conclusions: Our study reveals that ALG13-CDG is a disorder of brain-specific hypoglycosylation that disrupts key neurodevelopmental pathways and destabilizes cortical network function. Through integrated multiomic and functional analyses, we identify early network hypoactivity, mistimed neuronal maturation, and evolving E/I imbalance that progresses to compensatory hyperexcitability, providing a mechanistic basis for seizure vulnerability. These findings redefine ALG13-CDG as disorders of cortical network instability, offering a new framework for targeted therapeutic intervention. Full article

Hemophilia A (HA) is an X-linked recessive bleeding disorder that predominantly affects males but rarely manifests clinically in females. We report an unusual case of a woman with HA carrying a de novo heterozygous F8 variant, skewed X chromosome inactivation (XCI), and mosaic monosomy X without the Turner syndrome phenotype. DNA was extracted from whole blood. After excluding F8 inversions and large rearrangements, Sanger sequencing of coding regions was performed. XCI was assessed by STR analysis of the AR gene. Haplotypes were identified by fragment analysis of three polymorphic sites. Karyotyping was performed using G-banding. A heterozygous missense variant in the F8 gene, c.6545G>A (p.Arg2182His), was detected with allelic imbalance. STR analysis confirmed ~93% skewed XCI. Karyotyping revealed mosaicism: 45,X [7]/46,XX [14]. Neither parent carried the c.6545G>A variant or karyotype aberrations. We suggest that 46,XX cells carried c.6545G/A with preferential inactivation of the normal X chromosome, whereas 45,X0 cells carried the mutant allele only. The limited proportion of active normal X chromosomes led to a mild rather than severe phenotype. This case highlights complex genetic mechanisms underlying HA in females and underscores the importance of comprehensive molecular and cytogenetic testing for accurate diagnosis, clinical management, and genetic counseling. Full article

Germline mutations in the X-linked cohesin subunit gene SMC1A have been increasingly recognized as a cause of developmental and epileptic encephalopathy (DEE); however, the underlying basis of its marked phenotypic heterogeneity remains elusive. In our narrative review, starting from all literature-reported clinical cases of SMC1A-related DEE, we propose an integrative framework summarizing all the clinical and genetic features, stratified by mutation type, mosaic fraction, and X-chromosome inactivation (XCI) patterns to provide valuable support for genetic diagnosis and variants, found to date. Also, we discuss how somatic mosaicism and epigenetic variability underlie the clinical diversity of SMC1A-associated epilepsy and systematically describe the entire phenotypic spectrum, from early-onset, therapy-resistant seizures to milder intellectual disability profiles. We further examine how SMC1A mutations perturb cohesin’s canonical roles in chromatin loop formation and sister-chromatid cohesion, leading to widespread transcriptional dysregulation of neurodevelopmental gene networks. Evidence that XCI skewing can ameliorate or exacerbate neuronal cohesin deficits and, thus modulate seizure threshold, is presented. Full article

X chromosome inactivation (XCI) is a fundamental epigenetic process that balances X-linked gene expression between females and males by silencing one X chromosome in female cells. Variability or skewing of XCI can influence the clinical presentation of X-linked disorders. Bain type X-linked intellectual disability syndrome (MRXSB), caused by mutations in the X-linked HNRNPH2 gene, is characterized by intellectual disability, developmental delay, and neurological abnormalities. In female patients, XCI heterogeneity complicates disease modeling and therapeutic development. Induced pluripotent stem cells (iPSCs) offer a unique platform to study patient-specific disease mechanisms, but the dynamics of XCI during iPSC reprogramming, maintenance, and differentiation are not fully understood. In this study, we generated 12 iPSC clones from fibroblasts of a female MRXSB patient heterozygous for the HNRNPH2 c.340C > T mutation. Four clones expressed the mutant HNRNPH2 allele and eight expressed the wild-type allele, indicating X chromosome reactivation (XCR) followed by random XCI during reprogramming. Importantly, these XCI patterns remained stable during long-term iPSC propagation and subsequent differentiation into the three germ layers and neural stem cells. Our findings provide new insights into XCI and XCR dynamics in the context of X-linked neurodevelopmental disorders and emphasize the importance of careful clone selection for accurate disease modeling using iPSC-based approaches. Full article

Autoimmune diseases such as systemic lupus erythematosus and Sjögren’s syndrome show pronounced sex disparities in prevalence, severity, and clinical outcomes, with females disproportionately affected. Emerging evidence highlights sex-based differences in immune and inflammatory responses as key contributors to this bias. Genetic factors—including sex chromosomes, skewed X chromosome inactivation, and sex-biased microRNAs—as well as sex hormones and pregnancy modulate gene expression and immune cell function in a sex-specific manner. Additionally, sex hormone-dependent epigenetic modifications influence the transcription of critical immune regulators. These genetic and hormonal factors collectively shape the activation, differentiation, and effector functions of diverse immune cell types. Environmental factors—including infections, gut microbiota, environmental chemicals and pollutants, and lifestyle behaviors such as diet, smoking, UV exposure, alcohol and caffeine intake, physical activity, and circadian rhythms—further modulate immune function and autoimmune disease pathogenesis in a sex-dependent manner. Together, these mechanisms contribute to the heightened risk and distinct clinical features of autoimmunity in females. A deeper understanding of sex-biased immune regulation will facilitate the identification of novel biomarkers, enable patient stratification, and inform the development of sex-specific diagnostic and therapeutic strategies for autoimmune diseases. Full article

Rett syndrome (RTT) is a rare X-linked dominant neurodevelopmental disorder caused by pathogenic variants in the methyl-CpG-binding protein 2 (MECP2) gene, which encodes a methyl-CpG-binding protein (MeCP2) that acts as a repressor of gene expression, crucial in neurons. Dysfunction of MeCP2 due to its pathogenic variants explains the clinical features of RTT. Here, we performed histological and RNA analyses on a post-mortem brain sample from an RTT patient carrying the p.Arg106Trp missense mutation. This patient is part of a cohort of 56 genetically and clinically characterized RTT patients, for whom we provide an overview of the mutation landscape. In the RTT brain specimen, RT-PCR analysis detected preferential transcription of the mutated mRNA. X-inactivation studies revealed a skewed X-chromosome inactivation ratio (95:5), supporting the transcriptional findings. We also mapped the MECP2 transcript in control human brain regions (temporal cortex and cerebellum) using the RNAscope assay, confirming its high expression. This study reports the MECP2 transcript representation in a post-mortem RTT brain and, for the first time, the in situ MECP2 transcript localization in a human control brain, offering insights into how specific MECP2 mutations may differentially impact neuronal functions. We suggest these findings are crucial for developing RNA-based therapies for Rett syndrome. Full article

Background: Disruption of HCCS results in microphthalmia with linear skin lesions (MLS) characterized by microphthalmia/anophthalmia, corneal opacity, aplastic skin lesions, variable central nervous system and cardiac anomalies, intellectual disability, and poor growth in heterozygous females. Structural variants consisting of chromosomal rearrangements or deletions are the most common variant type, but a small number of intragenic variants have been reported. Methods: Exome sequencing identified variants affecting HCCS. Results: Three novel intragenic variants and two genomic deletions of HCCS were found in individuals with primarily ocular features of MLS. X-inactivation was highly skewed in affected individuals with all three intragenic variants. Corneal opacity was the most penetrant feature (100%). In addition, a duplication of uncertain significance including both HCCS and AMELX was identified in a male with corneal anomalies, glaucoma, an atrial septal defect, and enamel hypoplasia along with a family history of developmental ocular disorders consistent with X-linked inheritance. Conclusion: Although variable expressivity is a known feature of MLS, our findings provide additional support for including HCCS in testing for individuals with isolated ocular anomalies and provide further evidence for its association with congenital aphakia, aniridia/other iris defects, and corneal staphyloma/ectasia. Full article

Background: Fabry Disease (FD) is an X-linked lysosomal disease, in which, unlike other X-linked disorders, most female carriers manifest signs or symptoms for unknown reasons. Objectives: Herein, we aimed to test the potential role of X-chromosome inactivation (XCI) in leukocytes as a prognostic biomarker of disease in FD female carriers. Moreover, we explored if levels of X-inactive-specific transcript (Xist), a long non-coding RNA driving XCI, were detectable in the leukocytes of FD female carriers. Methods: We tested the XCI pattern in leukocytes on 33 consecutive females carrying pathogenic GLA variants. Disease severity was defined using the Mainz Severity Score Index (MSSI). Xist levels in leukocytes were assessed by real-time PCR and compared to the levels of 22 controls. Results: XCI was obtained for 31 female patients, finding 16 skewed (51.6%) individuals. Global MSSI did not differ in skewed vs. non-skewed FD carriers. In skewed FD females, the renal function and mean cardiologic MSSI subscore were significantly worse, and systemic arterial hypertension was more frequent. Xist levels detected in leukocytes were similar between female patients and controls, and did not differ by phenotype or XCI status. Conclusions: A skewed XCI pattern in leukocytes may represent a prognostic biomarker of worse renal and cardiac outcomes in female FD carriers. Full article

Background and Objectives: Recurrent pregnancy loss (RPL) is a multifactorial condition, encompassing genetic, anatomical, immunological, endocrine, as well as infectious and environmental factors; however, the etiology remains elusive in a substantial number of cases. Genetic factors linked to RPL include parental karyotype abnormalities (e.g., translocations, inversions, copy number variants), an increase in sperm aneuploidy, fetal microchimerism, severe skewing of X chromosome inactivation, and various gene polymorphisms. Our study aims to explore the value of routine conventional parental karyotyping in couples with RPL. Materials and Methods: A total of 213 couples (426 individuals) with a history of RPL were enrolled in this retrospective study. The peripheral blood samples included in this study were referred to the Human Genomics Laboratory of the University of Medicine and Pharmacy in Craiova, Romania, for conventional cytogenetic analysis between January 2013 and December 2023, by the Outpatient Medical Genetics Clinic of the Emergency Clinical County Hospital of Craiova. Chromosome analysis was performed using standard protocols and karyotypes were reported according to ISCN. Results: Out of 426 patients provided with conventional G-banded chromosome analysis, 410 had a normal karyotype (96.2%) and 16 had chromosome abnormalities (3.8%). The most common chromosomal abnormalities were reciprocal and Robertsonian translocations, with chromosomes 8, 11, 14, and 21 being most frequently involved. A single numerical anomaly was detected (47,XYY). One or multiple chromosomal polymorphisms were identified in 104 subjects (24.4%). In addition, we conducted a stratified analysis of the unselected group and detected chromosome abnormalities in only four cases (0.94%). Conclusions: Our results are consistent with recommendations for paternal karyotyping after an individual risk assessment in instances such as a previous live birth with congenital anomalies and/or the detection of unbalanced chromosomes or a translocation in product of conception or chorionic villi/amniotic fluid samples. In the absence of a positive history, blindly karyotyping couples may prove too expensive and labor intensive, while providing no information on fertility status or live birth rates. Full article

Germline variants in the phosphatidylinositol glycan class A (PIGA) gene, which is involved in glycosylphosphatidylinositol (GPI) biosynthesis, cause multiple congenital anomalies-hypotonia-seizures syndrome 2 (MCAHS2) with X-linked recessive inheritance. The available literature has described a pattern of almost 100% X-chromosome inactivation in mothers carrying PIGA variants. Here, we report a male infant with MCAHS2 caused by a novel PIGA variant inherited from his mother, who has a non-skewed pattern of X inactivation. Phenotypic evidence supporting the pathogenicity of the variant was obtained by flow-cytometry tests. We propose that the assessment in neutrophils of the expression of GPI-anchored proteins (GPI-APs), especially CD16, should be considered in cases with variants of unknown significance with random X-inactivation in carrier mothers in order to clarify the pathogenic role of PIGA or other gene variants linked to the synthesis of GPI-APs. Full article

Dystrophinopathies are the most common muscle diseases, especially in men. In women, on the other hand, a manifestation of Duchenne muscular dystrophy is rare due to X-chromosomal inheritance. We present two young girls with severe muscle weakness, muscular dystrophies, and creatine kinase (CK) levels exceeding 10,000 U/L. In the skeletal muscle tissues, dystrophin staining reaction showed mosaicism. The almost entirely skewed X-inactivation in both cases supported the possibility of a dystrophinopathy. Despite standard molecular diagnostics (including multiplex ligation-dependent probe amplification (MLPA) and next generation sequencing (NGS) gene panel sequencing), the genetic cause of the girls’ conditions remained unknown. However, whole-genome sequencing revealed two reciprocal translocations between their X chromosomes and chromosome 5 and chromosome 19, respectively. In both cases, the breakpoints on the X chromosomes were located directly within the DMD gene (in introns 54 and 7, respectively) and were responsible for the patients’ phenotypes. Additional techniques such as Sanger sequencing, conventional karyotyping and fluorescence in situ hybridization (FISH) confirmed the disruption of DMD gene in both patients through translocations. These findings underscore the importance of accurate clinical data combined with histopathological analysis in pinpointing the suspected underlying genetic disorder. Moreover, our study illustrates the viability of whole-genome sequencing as a time-saving and highly effective method for identifying genetic factors responsible for complex genetic constellations in Duchenne muscular dystrophy (DMD). Full article

Hemophilia A (HA), a rare recessive X-linked bleeding disorder, is caused by either deficiency or dysfunction of coagulation factor VIII (FVIII) resulting from deleterious mutations in the F8 gene encoding FVIII. Over the last 4 decades, the methods aimed at determining the HA carrier status in female relatives of HA patients have evolved from phenotypic studies based on coagulation tests providing merely probabilistic results, via genetic linkage studies based on polymorphic markers providing more accurate results, to next generation sequencing studies enabling highly precise identification of the causative F8 mutation. In parallel, the options for prenatal diagnosis of HA have progressed from examination of FVIII levels in fetal blood samples at weeks 20–22 of pregnancy to genetic analysis of fetal DNA extracted from chorionic villus tissue at weeks 11–14 of pregnancy. In some countries, in vitro fertilization (IVF) combined with preimplantation genetic diagnosis (PGD) has gradually become the procedure of choice for HA carriers who wish to prevent further transmission of HA without the need to undergo termination of pregnancies diagnosed with affected fetuses. In rare cases, genetic analysis of a HA carrier might be complicated by skewed X chromosome inactivation (XCI) of her non-hemophilic X chromosome, thus leading to the phenotypic manifestation of moderate to severe HA. Such skewed XCI may be associated with deleterious mutations in X-linked genes located on the non-hemophilic X chromosome, which should be considered in the process of genetic counseling and PGD planning for the symptomatic HA carrier. Therefore, whole exome sequencing, combined with X-chromosome targeted bioinformatic analysis, is highly recommended for symptomatic HA carriers diagnosed with skewed XCI in order to identify additional deleterious mutations potentially involved in XCI skewing. Identification of such mutations, which may profoundly impact the reproductive choices of HA carriers with skewed XCI, is extremely important. Full article