AIMS:To characterize the clinical, electrophysiological, and genetic spectrum of pediatric CMS and evaluate genotype-informed outcomes using an integrated phenotype-electrophysiology-genomics approach. METHODS:We retrospectively reviewed 36 pediatric CMS patients evaluated at a single center between 2015 and 2025. Clinical features, RNS, targeted NGS/WES variants, ventilator use, treatments, ACMG/AMP classifications, and MG-ADL outcomes were analyzed. RESULTS:Of 36 patients, 28 (77.8%) developed symptoms in the neonatal period or infancy. Biallelic variants involved 17 CMS genes; postsynaptic CMS was most common (55.6%, 20/36). COLQ and CHRNE were the most frequent genes (13.9%, 5/36 each), followed by CHAT (11.1%, 4/36). VUS were detected in 19 patients (52.8%, 19/36), including 8 with biallelic VUS supported by phenotype, neuromuscular transmission findings, treatment response, and follow-up. RNS showed a ≥ 10% decrement in 16/21 tested patients (76.2%). CHAT-CMS was associated with higher ventilator use (3/4 vs. 6/32; p = 0.041) and early mortality (3/4 vs. 1/32; p = 0.002). Median MG-ADL improved from 5 to 3 after genotype-informed therapy. CONCLUSION:Pediatric CMS shows marked genetic heterogeneity and frequent VUS-related uncertainty. Integrating phenotype, electrophysiology, and genomics supports diagnosis and mechanism-guided therapy. CHAT-CMS is high risk for early respiratory failure and mortality.

This study aims to explore the clinical characteristics of patients with NAD(P)HX metabolic deficiency and their prognosis after nicotinamide treatment. This study retrospectively analyzed the clinical characteristics, efficacy of nicotinamide treatment, and prognosis of patients with genetically confirmed NAD(P)HX metabolic defects admitted to Beijing Children’s Hospital from January 2016 to January 2025, as well as cases previously reported in the literature. The log-rank test was used for survival analysis, and the prognosis was evaluated using the Modified Rankin Scale (mRS). Nine patients were analyzed, including eight with NAXE deficiency and one with NAXD deficiency, seven of whom received nicotinamide treatment (180–500 mg/day). With a median follow-up of 3.92 years [range: 0.50–6 years, interquartile range (IQR) = 2.42 years], the overall prognosis was favourable. All seven treated patients survived, three of whom were able to attend school normally, and no significant adverse reactions were observed during treatment. Combined with previous studies, a total of 59 patients were included for analysis (14 cases of NAXD deficiency and 45 cases of NAXE deficiency), with an overall mortality rate of 66.7

AIM:To systematically characterize the phenotypic spectrum, neuroimaging features, heteroplasmy-phenotype correlation, and prognosis of the m.10191 T > C mutation. METHODS:We collected and analyzed data from 52 patients (14 newly recruited; 38 from literature). Phenotypes were pre-classified as Leigh syndrome (LS), Leigh-like syndrome (LLS), MELAS/LS overlap syndrome, and MELAS-like syndrome. Neuroimaging data were subjected to statistical analysis to explore inter-lesional associations and lesion-symptom correlations. Heteroplasmy level underwent k-means clustering and latent class analysis (LCA) to define data-driven subgroups and model genotype-phenotype correlations. Prognostic factors were evaluated through Bayesian logistic regression, and survival analysis was conducted. RESULTS:The cohort exhibited phenotypic heterogeneity, dominated by LS (46.2%). Key features included epilepsy, developmental delay, and dystonia. Globus pallidus involvement frequently co-occurred with midbrain and pontine lesions. Heteroplasmy level differed significantly across phenotypes. LCA identified three classes corresponding to clinical phenotypes. High heteroplasmy level, medullary involvement, and severe hyperlactatemia were associated with disease progression. Survival analysis indicated a 5 year survival rate of 80.0%, with high heteroplasmy level, hypotonia, and cerebellar lesions predicting poorer survival. INTERPRETATION:The m.10191 T > C mutation is linked to a continuous clinical spectrum correlated with heteroplasmy level. Specific clinical and neuroimaging features serve as valuable biomarkers for phenotypic classification and prognostic assessment.

OBJECTIVE:Mitochondrial diseases are the most common inherited metabolic disorders, characterized by pronounced clinical and genetic heterogeneity that complicates molecular diagnosis. Although DNA-based sequencing approaches have become standard in genetic testing, up to half of patients remain without a definitive diagnosis. We aimed to perform RNA sequencing (RNA-seq) of patient-derived skin fibroblasts to enhance the molecular diagnostic efficacy of mitochondrial disease in undiagnosed cases in China. METHODS:We performed RNA-seq on skin fibroblasts from 140 pediatric patients with suspected mitochondrial disease who remained genetically undiagnosed after whole exome sequencing (WES). Aberrant RNA expression and splicing were identified using the detection of RNA outliers pipeline (DROP). Based on WES findings, patients were stratified into a candidate group (n = 28), in which RNA-seq evaluated the pathogenicity of WES-identified variants of uncertain significance and an unsolved group (n = 112), in which RNA-seq was used to pinpoint candidate genes. In six cases where RNA-seq identified the aberrant RNA event but WES did not detect the causative variants, whole genome sequencing (WGS) was performed. RESULTS:Integrative RNA-seq, WES, and WGS analysis resulted in a genetic diagnosis in 25% of patients overall (20/28 [71%] in the candidate group; 15/112 [13%] in the unsolved group). Aberrant splicing explained most candidate-group diagnoses, including variants misclassified by in silico predictors such as SpliceAI. 14% of protein-truncating variants predicted to undergo nonsense-mediated decay (NMD) escaped degradation, highlighting the functional limits of current predictions. The variants identified in the unsolved cohort included synonymous, missense, deep intronic, near-splice-site variants, and large deletions. The most frequent among them was a recurrent synonymous East Asian founder mutation in ECHS1, accounting for seven cases. Interestingly, across 233 pathogenic variants associated with aberrant RNA phenotypes compiled from this study and prior reports, half were noncoding and half were coding variants. CONCLUSION:RNA-seq substantially enhances molecular diagnosis in mitochondrial disease by exposing cryptic splicing, regulatory, and NMD-escape events invisible to DNA sequencing alone. These data advocate transcriptome analysis as an essential component of comprehensive genomic diagnostics in neurometabolic disease.

This retrospective study on X-linked PDHA1-related pyruvate dehydrogenase complex (PDHc) deficiency combined a systematic literature review with a multicentre survey exploring genotypes, phenotypes and survival. Data from 891 individuals (45% unpublished) were included. Of note, 53% of cases were females. Median age at last assessment was 6 years (range 0-80 years, n = 622). We detected 331 different (118 unpublished) PDHA1 variants, of which 75% (305/405) had occurred de novo. Variants in this study were uploaded to ClinVar (SCV006297015-SCV006297345). The 10 most frequent variants accounted for 36% of the diagnoses. Sixty-nine per cent of the variants were private; missense (50%) and frameshift (20%) variants were most common. Frameshift/nonsense (FS/N) variants in males (44/401, 11%) were confined to regions escaping nonsense-mediated decay (NMD) and were significantly less frequent than in females (151/461, 33%). Neonatal or infantile (405/529, 77%) presentations were most frequent, with pre/perinatal abnormalities reported in 47% (159/342). FS/N variants in the NMD-predicted region 3.9 [95% confidence interval (CI) 1.54-11.04] times increased the odds of fetal findings. Females presented significantly earlier [2 months, interquartile range (IQR) 7.0, n = 224] than males (8 months, IQR 16.6, n = 233), with increased risk of neonatal presentation [odds ratio (OR) 3.01 (95% CI 1.279-7.616)] when harbouring FS/N variants in the NMD-predicted region. The overall (n = 242) mean survival time was 10.9 (95% CI 9.9-11.9) years. On average, females survived 4.5 (95% CI 2.62-6.40) years longer than males despite presenting more severe phenotypes. Poor survival was associated with male sex [hazard ratio (HR) 3.3 (95% CI 1.95-5.62)], neonatal presentation [HR 5.5 (95% CI 2.17-14.09)], FS/N variants in the NMD-predicted region [HR 4.0 (95% CI 1.78, 9.16)] and splice variants [HR 2.3 (95% CI 1.15, 4.59)]. More severe clinical phenotypes were predicted by neonatal or infantile presentations and by female sex. Developmental delay (DD), intellectual disability (ID), muscle hypotonia, abnormal movements, seizures, feeding difficulties and microcephaly were the most frequent phenotypes, all occurring in more than half. Corpus callosum or basal ganglia alterations and cerebral atrophy were common. Four per cent (36/891) were reported to have mild phenotypes with no DD nor ID (25/36 males). This is the largest dataset on a nuclear-encoded defect of mitochondrial energy metabolism. The genotypic and phenotypic details further defines the disease landscape and can be used for variant interpretation. The correlations between genotypes, sex, phenotypes and survival, adds substantial improvement to counselling.

Heterozygous missense mutations in MORC2 have been implicated in various clinical entities, ranging from early-onset neurodevelopmental disorders to late-onset neuropathies. The mechanism underlying the phenotypic heterogeneity and pleiotropic effects of MORC2 has remained elusive. Here, we analysed blood and fibroblast DNA methylation, transcriptomes, proteomes and phenotypes of 53 MORC2 patients. We identified a MORC2-specific DNA methylation episignature that is universal across all MORC2-associated phenotypes and conserved across different tissues. The MORC2 episignature consists mainly of DNA hypermethylation in promoter regions, leading to transcriptional repression of target genes resulting in a MORC2-specific RNA signature. Concomitant downregulation of three disease-associated genes-ERCC8, NDUFAF2 and FKTN-at different levels mirrors the variable biochemical defects and clinical manifestations observed in MORC2 patients. Silencing of NDUFAF2 accounts for the Leigh syndrome manifestation, whereas dysmorphic features are due to the repression of ERCC8. Overall, we showed that pathogenic MORC2 variants cause specific episignature, whereby methylation level variability and its repression impact on target genes explains the pleiotropy and predicts phenotypic heterogeneity in MORC2-related disorders. We predict that epigenetic variation may underlie pleiotropy in other Mendelian disorders.

Background:Reversible infantile respiratory chain deficiency (RIRCD) is a rare mitochondrial myopathy caused by homoplasmic MT‑TE m.14674T>C/G variants, characterized by severe infantile onset followed by spontaneous recovery. Nuclear modifiers are thought to modulate its incomplete penetrance, but evidence for digenic inheritance remains limited. We aim to analyze the clinical, genetic, and prognostic features of RIRCD, explore the roles of nuclear modifiers and digenic inheritance. Case Description:We report three Chinese RIRCD patients carrying the homoplasmic m.14674T>C variant. All presented with recurrent respiratory infections and feeding difficulties, with gradual developmental recovery after 1 year of age. Notably, we report a case of a homoplasmic m.14674T>C variant (maternal) and a pathogenic EARS2 heterozygous variant (paternal), indicating digenic inheritance of EARS2. Additionally, we report another case of a homoplasmic m.14674T>C variant and a maternally inherited CLCN4 variant associated with language delay and autistic features after recovery from RIRCD, suggesting the presence of additional modifiers or comorbidities. Among 52 published cases and our 3 new cases, 92.16% of cases had onset within 3 months, 85.55% had neuromuscular symptoms, 70.91% required nasogastric feeding, and 43.63% needed mechanical ventilation. Elevated lactate and creatine kinase levels, ragged-red fibers, and mitochondrial ultrastructural abnormalities in muscle biopsies were common pre-recovery. Respiratory chain deficiencies included isolated complex IV and combined I + IV defects. Prognosis was favorable (32.00% full recovery, 58.00% mild residual myopathy). Twenty-four cases (43.64%) had nuclear modifiers, including EARS2 (n=9) and TRMU (n=6). Conclusions:RIRCD is a rare mitochondrial myopathy caused by mitochondrial DNA (mtDNA) variants with penetrance regulated by nuclear modifiers. Digenic inheritance contributes to phenotypic heterogeneity, supporting precise diagnosis and future therapy.

OBJECTIVE:Pathogenic variations in the mitochondrial genome are tightly linked to neurological mitochondrial disorders in children. However, the mutation spectrum of mitochondrial DNA (mtDNA) in the Chinese population remains incomplete. Therefore, the primary objective of our study was to comprehensively characterize pathogenic mtDNA variants in Chinese children with mitochondrial disorders at clinical, molecular, and functional levels. METHODS:Between February 2019 and September 2023, we analyzed pathogenic mtDNA variants in a cohort of over 600 Chinese children suspected of having mitochondrial disorders. Whole-exome sequencing (WES) and whole-mtDNA sequencing were performed on the cohort. RESULTS:We identified 54 pathogenic or likely pathogenic mtDNA variants in 227 Chinese children with neurological mitochondrial disorders. Among the eight novel heteroplasmic variants detected in seven patients, in silico analyses suggested likely pathogenic features. Functional analyses using either primary fibroblasts or cybrid cells carrying different mutant loads of mtDNA variants showed impaired mitochondrial respiration, ATP generation, and mitochondrial membrane potential in five of the eight novel variants, including m.4275G>A, m.10407G>A, m.5828G>A, m.3457G>A, and m.13112T>C. The m.8427T>C variant was identified as a rare polymorphism because, despite being located at MT-ATP8, it does not affect both the assembly and activity of mitochondrial complex V in cells carrying homoplasmic m.8427T>C variation. Transcriptome profiling further confirmed the pathogenic contributions of these five variants by altering mitochondrial pathways. CONCLUSION:In summary, we revisited the mtDNA mutation spectrum in Chinese children with mitochondrial disorders, and identified five novel pathogenic mtDNA variants with functional verification that are related to neurological mitochondrial disorders in children.

The aim was to summarise the clinical characteristics of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), evaluate patient survival status, and identify prognostic factors. This retrospective study enrolled 150 children with MELAS from 07/2004 to 07/2023. The patients were followed up for a median of 3.37 years (IQR: 2.07–6.16 years). Disease burden was assessed using the Newcastle Pediatric Mitochondrial Disease Scale (NPMDS), and Spearman’s correlation coefficient was used to analyse factors affecting disease severity. The Kaplan–Meier and Cox proportional methods were used for survival analysis. Overall, 150 patients (73 male) were enrolled, of whom 118 were followed up and 22 died. The mean age at onset was 8.2 years (0.4–15.3), and stroke-like episodes were the most common initial symptoms (54

The absence of HIBCH or ECHS1, two Leigh syndrome genes, in cultured cells results in abnormal mitochondrial morphology and respiratory defects. Fly eyes lacking either protein exhibit age-dependent degeneration. Elevated lysine methacrylation (Kmea) is observed in both HIBCH- and ECHS1-deficient cells and fly tissues. Quantitative mass spectrometry reveals that many proteins are ectopically modified by Kmea in these cells. Mimicking Kmea in proteins like CH60, FKBP4, BIP, LDHB, or DHRS2 replicates the mitochondrial morphology changes seen in HIBCH- or ECHS1-deficient cells. Reducing Kmea modification partially rescues mitochondrial morphology changes in cells and eye degeneration in flies. Fibroblasts from patients with HIBCH or ECHS1 mutations show similar mitochondrial changes and elevated Kmea, which are significantly reversed by administering N-acetyl-L-cysteine to reduce Kmea levels. We propose that ectopic Kmea modification mediates the defects caused by HIBCH- or ECHS1-deficiency. Reducing Kmea modification provides a new approach for treating HIBCH- or ECHS1-related Leigh syndrome.

BackgroundB3GALNT2 mutations cause α-dystroglycanopathy (α-DGP), a rare condition characterized by muscular dystrophy, brain malformations, and developmental delay. However, its pathogenic mechanisms remain poorly understood. To date, limited cases have been reported, and the pathogenic mechanisms remain incompletely understood.MethodsClinical and genetic data from 3 newly diagnosed Chinese patients and 28 patients previously diagnosed with B3GALNT2-related α-DGP were analyzed. Using patient-derived fibroblasts, α-dystroglycan (α-DG) glycosylation and laminin-binding capacity were assessed by immunoblotting, laminin overlay and immunofluorescence. B3GALNT2 mRNA and protein levels were quantified by real-time PCR and immunoblotting. Enzymatic activity was measured using purified recombinant B3GALNT2 proteins. Differentially expressed genes were identified via an mRNA microarray.ResultsAll three patients carried compound heterozygous variants involving one truncating and one missense mutation. Two novel mutations (c.657_658insTT and c.1384T > C) were identified. Functional studies confirmed that the missense mutations (Y436C and C462R) impaired enzymatic activity to 40-50% of wild-type levels, while splice variants caused frameshifts and likely complete loss of protein. Despite partial residual activity, all patients showed severely reduced α-DG glycosylation and loss of laminin binding, consistent with a functional threshold effect. Transcriptomic analysis revealed upregulation of CHST10 in two patients.ConclusionsThis study expands the mutational spectrum of B3GALNT2-related α-DGP and provides mechanistic insight into the pathogenicity of novel variants. Our findings support a functional threshold model for B3GALNT2 activity in α-DG glycosylation and suggest CHST10 as a potential transcriptional responder to glycosylation defects. These results deepen the understanding of B3GALNT2-related dystroglycanopathies and may inform future diagnostic and therapeutic strategies.

Background Reversible infantile respiratory chain deficiency (RIRCD) associated with homoplasmic MT-TE m.14674T > C/G variants is characterized by severe infantile crisis followed by spontaneous recovery. Nuclear genetic modifiers may influence its phenotypic penetrance. Methods We analyzed the clinical profiles, genetic profiles, and prognosis of three patients with RIRCD and 55 published cases. Results Among the 55 cases, almost cases developed symptoms within the first 6 months. Neuromuscular symptoms were reported in 85.5%, with nasogastric feeding required in 70.9%, and mechanical ventilation in 43.6%. Pre-recovery biomarkers showed elevated lactate and creatine kinase levels. Muscle biopsies revealed ragged-red fibers, vacuolar changes, and mitochondrial ultrastructural abnormalities in most cases. Respiratory chain deficiencies included isolated complex IV and combined I + IV defects. The prognosis of RIRCD was favorable. In total, 32.0% of patients were healthy, and 58.0% had mild residual myopathy. Genetically, 96.4% harbored the homoplasmic m.14674T > C variant. Whole-exome sequencing identified nuclear modifier genes in 24 cases, including EARS2 (n = 9) and TRMU (n = 7). We reported a case of a homoplasmic m.14674T > C variant (maternal) and a pathogenic EARS2 heterozygous variant (paternal), indicating digenic inheritance of EARS2. Additionally, we reported another case of a homoplasmic m.14674T > C variant and a maternally inherited CLCN4 variant associated with RIRCD post-recovery language delay and autistic features, suggesting the presence of additional modifiers or comorbidities. Conclusion RIRCD is a rare, reversible mitochondrial myopathy, driven by homoplasmic MT-TE m.14674T > C/G variants but influenced by nuclear modifiers (e.g. EARS2) for penetrance. Understanding these modifier genes and digenic inheritance offers insights into phenotypic heterogeneity and may guide future therapy.

MTERF3, a negative regulator of mtDNA transcription, was first identified in 2007.Recent studies have revealed the pivotal role of MTERF3 throughout the entire lifecycle of mtDNA. However, no disease phenotypes have been linked to this gene till now. Genetic testing was performed on two unrelated families. Mitochondrial respiration and OXPHOS complex activity were assessed in patient-derived fibroblasts. An MTERF3 knockdown HEK293 cell line was generated, followed by rescue experiments with wild-type and mutant MTERF3. Two patients mainly presented with developmental delay. Genetic testing identified compound heterozygous variants c.635dup p.(Asn212Lysfs*7) and c.1055C > T p.(Pro352Leu) in Patient 1, and a homozygous variant c.943A > Gp.(Met315Val) in Patient 2. Patient's fibroblasts and MTERF3 knockdown cells showed impaired mitochondrial respiration and reduced levels of OXPHOS complexes I, III, and IV. Transcription of MT-ND5, ND6, COII, and COIII was reduced, while other mitochondrial genes were upregulated. Wild-type MTERF3 expression restored these defects, but the variant Pro352Leu from patient failed to rescue mitochondrial dysfunction. This study identifies a novel mitochondrial disease phenotype and establishes the first association with MTERF3, expanding the mitochondrial disease spectrum and offering insights into the clinical relevance of the MTERF family.

Background The prevalence of mitochondrial diseases is increasing, leading to a significant economic burden on families and society. However, nationwide cost data on their effects on China’s economy remain limited. This study aimed to investigate the economic cost of mitochondrial diseases in Chinese children, analyse the relevant influencing factors, and provide a foundation for strategies to reduce the healthcare burden. Methods In this single-centre, cross-sectional study, an online questionnaire was randomly administered to paediatric patients diagnosed with mitochondrial diseases between January 2012 and January 2022. The questionnaire included questions regarding demographic data, clinical information, and expenditure-related costs. Multivariate analysis of economic cost was performed using a generalised linear gamma conjugate model (A1). Results The responses to 102 questionnaires were analysed. The median direct economic cost incurred for the diagnosis of mitochondrial disease was $8,520.19, with direct medical and non-medical costs of $6,769.06 and $2,092.98, respectively, and an indirect cost of $3,162.93. Healthcare insurance covers 27.29% of direct medical expenses. Multivariate analysis showed that the economic cost of diagnosing mitochondrial diseases was significantly correlated with the year of disease onset ( P < 0.001). The median annual economic cost for treatment and symptom management after diagnosis was $12,292.79, with direct medical and non-medical costs of $10,887.53 and $1,360.44, respectively, and an indirect cost of $5,442.21. Healthcare insurance covered only 15.16% of direct medical expenses. No significant differences were observed between the subgroups after diagnosis and the annual economic costs of treatment or symptom management. Conclusion The study findings indicated that the economic burden of both the diagnosis and treatment of patients with mitochondrial diseases was substantial. Increased emphasis should be placed on primary and secondary prevention strategies to further reduce the overall economic burden of rare genetic diseases, such as mitochondrial diseases.

OBJECTIVE:To summarize clinical characteristics of the largest Chinese cohort of mitochondrial short-chain enoyl-CoA hydratase-1 deficiency (ECHS1D) and analyze the genotype-phenotype correlations. METHODS:This retrospective study enrolled 42 children with genetically diagnosed ECHS1D within the China Mitochondrial Disease Network. Patients were classified into severe infantile (SI), slowly progressive infantile (SPI), and late-onset phenotype (LP) based on onset age, disease progression rate, and gross motor impairment severity. Prognosis was assessed using the Modified Rankin Scale(mRS). RESULTS:Forty-two patients (25 male) were included, with a median onset age of 13.5 months (range 3-60). Paroxysmal dystonia (PD, 33.3 %) was the most common initial symptoms, followed by developmental delay(28.6 %) and regression(21.4 %). All patients had globus pallidus involvement and were diagnosed with Leigh syndrome (SI, n = 18; SPI, n = 13; LP, n = 11). SI cases all started with non-paroxysmal dystonia, and showed more frequent putamen (77.8 %) and caudate nucleus (72.2 %) involvement. In SPI and LP cases, PD was more common at onset, with milder symptoms and often isolated globus pallidus involvement. The proportions of elevated urinary metabolic markers 2,3-dihydroxy-2-methylbutyrate (2,3DH2MB) and S-(2-carboxypropyl) cysteamine (SCPCM) were 89.7 % and 93.1 % respectively, and the degree of their elevation was significantly correlated with phenotype severity. Regarding overall prognosis, 52.4 % of patients could walk independently (mRS < 4), with three fatalities. SI cases had the worst prognosis, followed by SPI, while LP cases showed the best outcomes (p < 0.05). In terms of genetics, all patients were compound heterozygous variants in the ECHS1 gene, with 21 novel variants identified. The most common variant was the c.489G > A (p.Pro163=) variant, which was found in 18 patients, accounting for as high as 42.8 % (allele frequency 0.214). And patients carrying this synonymous variant exhibited later onset age, longer diagnostic duration, milder phenotypes. CONCLUSIONS:This study provides a comprehensive overview of ECHS1D, summarizing its clinical and genetic spectrum, and indicating that the c.489G > A variant is a potential hotspot in the Chinese population. As findings from single-center studies may not be generalizable to a broader population, multi-center prospective studies are warranted.

BackgroundThe MRPS36 gene encodes the E4 subunit of the 2-oxoglutarate dehydrogenase complex (OGDHC), a critical enzyme in the tricarboxylic acid cycle. OGDHC deficiency can lead to metabolic disorders with a clinical spectrum ranging from fatal neonatal lactic acidosis to variable degrees of global developmental delay and movement disorders. To date, a homozygous MRPS36 variant has been reported as a novel cause of Leigh syndrome in only two siblings, who presented with developmental delay, movement disorders, bilateral striatal necrosis, and reduced OGDHC activity.Case presentationWe report a third case of Leigh syndrome associated with MRPS36 variants in a 2-year-old boy. The patient exhibited with global developmental delay, dystonia, early-onset chorea, and elevated serum lactate levels. Follow-up brain magnetic resonance imaging at 2 years revealed progressive degenerative lesions in the bilateral basal ganglia. Muscle biopsy showed abnormal mitochondrial accumulation beneath the sarcolemma, and the oxygen consumption rate was reduced in skin fibroblasts. Whole-exome sequencing identified two novel compound heterozygous MRPS36 variants: c.42+1G>A (p.?) and c.296G>C (p.Arg99Pro).ConclusionThis case supports MRPS36 as a novel pathogenic cause of Leigh syndrome, further expanding the genetic spectrum of the disorder. Key clinical features include developmental delay, involuntary movement disorders, progressive basal ganglia atrophy, and a slowly progressive disease course.

This study investigated clinical and genetic characteristics of Chinese pediatric patients with single large-scale mitochondrial DNA deletions (SLSMD). We analyzed 28 patients (July 2004-March 2025) using long-range PCR and next-generation sequencing. Spearman correlation and ANOVA assessed genotype-phenotype relationships. Patients (mean age 5.52 ± 3.96 years) exhibited multi-organ involvement (5.43 ± 1.87 organs). Common initial presentations included ocular (29%), neurologic, and endocrine dysfunction. Only 14.3% had the classic 4977 bp deletion, and 23 novel deletions were identified in 25 patients. Larger deletions correlated with more deleted MRC complexes (r = 0.516, p = 0.0123) and more deleted tRNAs (r = 0.534, p = 0.0103). Kearns-Sayre syndrome (KSS) patients had later onset (p = 0.0337), larger deletions (p = 0.0263), and greater tRNA/MRC complex (p = 0.0263, p = 0.0319) involvement than non-KSS patients. SLSMD in Chinese children primarily causes KSS, Pearson syndrome (PS), and progressive ophthalmoplegia with multi-organ involvement. Genotype-phenotype correlations exist, particularly between deletion size, onset age, and disease severity. KSS patients show distinct genetic and clinical profiles, suggesting slower progression. This study expands the known SLSMD spectrum and underscores mitochondrial testing in pediatric multi-organ disorders.

NAD(P)HX dehydratase (NAXD) gene is one of the key enzymes encoding the nicotinamide nucleotide repair system, reportedly associated with Encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy, 2 (PEBEL2). Here, we generated an induced pluripotent stem cell (iPSC) line from the dermal fibroblasts (HDFs) of a PEBEL2 patient who carried biallelic mutations, c.101_102delTA(p.Thr35Phefs*63) and c.318C > G (p.Ile160Met) in NAXD. These iPSCs showed stable amplification in vitro, expressed pluripotent markers, and differentiated spontaneously into three germ layers, as well as NAXD mutations with normal karyotype.

The MELAS/Leigh overlap syndrome manifests with a blend of clinical and radiographic traits from both MELAS and LS. However, the association of MELAS/Leigh overlap syndrome with MT-CO1 gene variants has not been previously reported. In this study, we report a patient diagnosed with MELAS/Leigh overlap syndrome harboring the m.5906G > A variant in MT-CO1, with biochemical evidence supporting the pathogenicity of the variant. The variant m.5906G > A that led to a synonymous variant in the start codon of MT-CO1 was filtered as the candidate disease-causing variant of the patient. Patient-derived fibroblasts were used to generate a series of monoclonal cells carrying different m.5906G > A variant loads for further functional assays. The oxygen consumption rate, ATP production, mitochondrial membrane potential and lactate assay indicated an impairment of cellular bioenergetics due to the m.5906G > A variant. Blue native PAGE analysis revealed that the m.5906G > A variant caused a deficiency in the content of mitochondrial oxidative phosphorylation complexes. Furthermore, molecular biology assays performed for the pathogenesis, mtDNA copy number, mtDNA-encoded subunits, and recovery capacity of mtDNA were all deficient due to the m.5906G > A variant, which might be caused by mtDNA replication deficiency. Overall, our findings demonstrated the pathogenicity of m.5906G > A variant and proposed a potential pathogenic mechanism, thereby expanding the genetic spectrum of MELAS/Leigh overlap syndrome.

Abstract Introduction: Given sparse RW evidence, we assessed biomarker characteristics & clinical outcomes in community oncology practices among pre-treated non-MSI-H/dMMR mCRC patients. Methods: This retrospective cohort study used structured & chart review data from iKnowMed, The US Oncology Network electronic health record data & included non-MSI-H/dMMR adult mCRC patients pre-treated with standard of care (SoC) chemo who initiated subsequent systemic anticancer treatment (SACT), best supportive care (BSC) or neither from 1/1/2016 - 12/31/2021. Index date for SACT users was the regimen start date post SoC chemo & for patients on BSC & no SACT/BSC, it was last chemo administration date. Patients were followed from index date until 8/31/2022 for overall survival (OS) & real-world progression-free survival (rwPFS). KM analyses assessed outcomes, overall & stratified by treatment, RAS status & metastasis sites. Results: Of mCRC patients with >2 visits, 70.9% received MSI/MMR testing. In 292 eligible chart review patients, 69.5% received SACT in pre-treated setting (regorafenib 14.8%, trifluridine/tipiracil (TAS-102) 12.3%, other 72.9%), 28.8% received BSC & 1.7% neither. 76.7% reported KRAS/NRAS testing with 60.7% wild-type & 39.3% mutant. Common metastasis sites were liver-only (44.2%), liver & lung (10.3%) & lung-only (8.9%). Median (range) duration of follow-up was 5.2 (2.7, 10.0) months for regorafenib, 5.3 (2.5, 8.6) for TAS-102 & 10.7 (5.3, 18.0) for the other treatments group. Median OS was 7.4 (95% CI: 5.8, 8.8) months & median rwPFS was 3.5 (95% CI: 3.2, 4.3) months (outcomes data in Table). Conclusions: 29.1% pre-treated, mCRC patients did not receive guideline recommended MSI/MMR testing, highlighting the need to improve testing. Outcomes varied by treatment, RAS status, & metastatic sites. The modest RW clinical benefit for SoC regorafenib & TAS-102, was consistent with trials & other RW studies; all highlighting an unmet need. Cohorts Median (95% CI) OS (months) Median (95% CI) rwPFS1 (months) Overall 7.4 (5.8, 8.8) 3.5 (3.2, 4.3) Regorafenib 5.6 (3.1, 9.7) 2.4 (1.8, 3.0) TAS-102 5.9 (3.4, 8.6) 3.0 (2.1, 3.4) Other SACT2 12.8 (9.8, 17.2) 4.9 (3.7, 5.8) BSC 2.4 (1.8, 3.2) - RAS mutation Wild-type 8.6 (6.6, 11.5) 4.0 (3.3, 4.9) Mutant 5.4 (3.4, 9.5) 3.2 (2.1, 4.6) Metastatic sites Liver only 8.0 (5.7, 11.7) 3.9 (3.0, 4.9) Lung only 17.0 (7.8, 35.6) 7.9 (3.3, 10.5) Liver & lung only 5.4 (2.4, 7.2) 3.5 (2.1, 5.4) Other 6.7 (4.1, 9.4) 3.2 (2.7, 3.9) Abbreviation: CI: confidence interval, TAS-102: trifluridine/tipiracil, OS: overall survival, rwPFS: real-world progression-free survival, SACT: systemic anticancer treatment 1Overall rwPFS was calculated among patients receiving subsequent SACT only (n = 203) 2Top 2 “other SACT” included irinotecan- or oxaliplatin-based treatment Citation Format: Mayur M. Amonkar, Sneha Sura, Kaushal Desai, Rishi Jain, Zhimei Liu, Nicole Niehoff, Thomas W. Wilson, Gregory Patton, David Cosgrove. Real-world (RW) biomarker characteristics and clinical outcomes in pre-treated non-MSI-H/dMMR metastatic colorectal cancer (mCRC) patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 927.