チャージ症候群

Both RIT1 and RIT2 are members of the RAS superfamily of small GTPases, which regulate various cellular processes. RIT1 is widely expressed, whereas RIT2 is primarily found in neuronal tissues. Dysregulation of these proteins has been associated with several human diseases, including Noonan syndrome, cancer, Parkinson's disease, autism, and schizophrenia. Although RIT1 and RIT2 are often compared to classical RAS proteins, they exhibit distinct regulatory and biochemical properties. Here, we demonstrate that RIT1 differs from classical RAS in GTPase cycling. Unlike classical RAS proteins, RIT1 did not respond to SOS1-mediated nucleotide exchange or p120GAP-stimulated GTP hydrolysis under cell-free conditions. These results imply that RIT1 may depend on regulatory mechanisms that differ from those of classical RAS proteins. However, the relevant physiological regulators remain unknown. Disease-associated RIT1 mutations cluster around the P-loop and Switch II regions. In this transient overexpression screening system, however, these mutations had only a modest effect on the canonical MAPK, PI3K/AKT, and JNK signaling pathways in HEK293T overexpression experiments. This suggests the existence of additional context-specific effectors and regulatory factors. We demonstrate that RIT1 and RIT2 interact with membrane lipids via a basic C-terminal extension. The KRLK-containing region contributes to the binding of phosphatidylserine and phosphoinositides. Charge-reversal mutations disrupt lipid interactions and liposome binding, supporting the functional importance of this region. In a reconstituted liposome system, galectin-3 and LZTR1, but not galectin-1, reduced the interaction of GDP-loaded RIT1 and RIT2 with liposomes. These results suggest that accessory proteins may influence RIT membrane interactions. However, their cellular relevance requires further validation. Together, our findings provide biochemical insights into RIT GTPase regulation and its interactions with membrane lipids under cell-free conditions.

The emergence of resistance-associated mutations in coronavirus main protease (Mpro) poses a significant challenge to the development of broad-spectrum antiviral therapeutics. In this study, we improved and accelerated a mutation-aware machine learning (ML) framework to predict the binding score of Nirmatrelvir analogue ligands against wild-type and mutant MERS-CoV Mpro. A library of 15,889 Nirmatrelvir derivatives generated through systematic scaffold modification was docked against the wild-type and five variants of the Mpro, producing a total of 95,334 structural and docking score datasets of these protein-ligand complexes. During the ML model development phase, ligand effects were learned from RDKit molecular descriptors and graph-based representations, and the mutation-induced effects were captured through delta-encoded physicochemical properties (hydrophobicity, charge, aromaticity, and polarity) of the active-site residues. Among the evaluated models, the CatBoost regressor tree-based algorithm achieved the lowest mean absolute error (MAE) value of 0.23 Kcal/mol and an R2 of 0.87. Further improvement was achieved by creating a weighted ensemble model combining the CatBoost regressor, XGBoost and LightGBM regressor, resulting in a prediction accuracy with a MAE of 0.19 Kcal/mol and an R2 of 0.90 relative to docking scores. Model robustness was further evaluated through random-, ligand group- and scaffold group- K-fold cross-validation along with their Y-randomization. Moreover, the models were also tested with a new set of 1000 structurally diverse compounds. SHAP analysis was conducted, which identified 20 molecular descriptors critical for accurate predictions. The ensemble model accurately predicted the binding affinities of Nirmatrelvir and its four analogues (E1-E4), reproducing the experimental pIC50 trend and correctly identifying the most potent inhibitors. The ensemble model also showed consistent performance across all MERS-CoV Mpro variants, S147Y, S142G, L144A, S142G/S147Y, and S142G/L144A/S147Y, demonstrating its potential for rapidly discovering mutation-resistant antiviral drugs.

BACKGROUND: CHARGE syndrome (OMIM #214800) is a rare autosomal dominant multisystem disorder, most commonly attributable to de novo heterozygous loss-of-function pathogenic variants in the CHD7 gene. Pathogenic Pathogenic variants of CHD7 are distributed throughout the entire coding region, with nonsense and frameshift pathogenic variants predominating, and the vast majority constitute private mutations. Owing to its broad phenotypic spectrum and marked variability in expressivity, early diagnosis remains challenging. This article presents the long-term follow-up data of a female patient with genetically confirmed CHARGE syndrome, with particular emphasis on her clinical trajectory and outcomes achieved through multidisciplinary management. CASE PRESENTATION: The patient was a full-term female born via spontaneous vaginal delivery in 2017, presenting with respiratory distress and feeding difficulties immediately after birth. Comprehensive evaluation revealed multisystem abnormalities involving the respiratory, cardiovascular, neurological, and sensory systems. Trio-based whole-exome sequencing identified a de novo heterozygous nonsense pathogenic variant, c.6292(EXON31)C>T (p.Arg2098*), in the CHD7 gene. Literature review indicated that this pathogenic variant had been previously reported in cases that all resulted in infantile death. In contrast, our patient, following active multidisciplinary management, achieved significant improvement in multiple organ functions and survived to school age, where she now adapts well to a special education school environment. This case provides the first evidence that this pathogenic variant is compatible with a favorable long-term outcome, highlighting substantial phenotypic heterogeneity and prognostic diversity even among individuals carrying an identical genetic alteration. CONCLUSION: This case highlights the critical importance of early genetic diagnosis and coordinated multidisciplinary management in CHARGE syndrome. By presenting divergent outcomes associated with the same pathogenic variant, our findings enrich the clinical evidence on CHD7 genotype-phenotype correlations. Even with severe neonatal multisystem involvement, proactive and individualized management can achieve favorable long-term outcomes.

CHARGE syndrome is a rare congenital disorder primarily attributed to heterozygous pathogenic variants of the CHD7 gene. Most pathogenic CHD7 variants are loss-of-function (LoF) variants, whereas the interpretation of missense variants remains challenging in the absence of functional evidence for their pathogenicity. We report a female infant presenting with clinical features characteristic of CHARGE syndrome. Targeted sequencing identified a heterozygous CHD7 variant (NM_017780.4:c.5273A>G), initially annotated as a missense substitution p.Asp1758Gly. This variant has been previously reported and registered with conflicting pathogenicity classifications; however, its transcript-level consequences remain unclear. Long-PCR-based RNA sequencing of total RNA from peripheral blood mononuclear cells revealed two aberrant splicing patterns associated with the variant: a predominant transcript carrying a 28-bp deletion due to cryptic donor splice-site activation, and a minor transcript with partial intron 24 retention. Both transcripts were predicted to result in premature termination codons. These findings demonstrate that c.5273A>G functions as a LoF variant through dual aberrant splicing rather than a simple missense substitution. This case underscores the importance of RNA-level splicing analysis for the accurate interpretation and classification of CHD7 missense variants.

Developmental senescence has recently emerged as a physiological program that contributes to tissue remodeling, morphogenesis and growth regulation during vertebrate embryogenesis. While transient and non-pathological under normal conditions, this program requires strict spatial and temporal control. Here we argue that its misregulation represents a source of congenital defects. In particular, we suggest that the deficiency of the chromatin remodeler CHD7, the major genetic cause of CHARGE syndrome, may disrupt the spatiotemporal boundaries of developmental senescence. This hypothesis is supported by several lines of evidence in vertebrate models: first, CHD7 expression domains during development largely overlap with regions where physiological embryonic senescence has been described. Second, CHD7 reduction is associated with altered cell proliferation and misregulation of key senescence-related pathways including those driven by p53, p21 and TGFβ. Disruption of this regulatory balance may alter the timing of cellular growth arrest, clearance and tissue differentiation, providing a plausible mechanistic framework for the multisystemic anomalies observed in CHARGE syndrome.