Human Mutation

Our labs have been studying neurofibromin function and phenotype for over a decade with the intent of generating targeted therapeutics for Neurofibromatosis type 1 (NF1). In the process, we have generated numerous human cell lines containing variants within the NF1 gene. Herein, we present data characterizing these cell lines and make them publicly available for use by researchers both within and outside the NF1 community. We describe lines that contain both well-characterized patient-specific variants either at their endogenous locus or as exogenous cDNAs, as well as variants of uncertain significance (VUS), engineered as heterozygous, homozygous, and compound heterozygous variants. Methods to generate each line and subsequent validation steps are detailed including targeted sequencing, Western blot analysis for neurofibromin expression and ERK activation. The utility of each line is dependent on the variant of interest, the parental cell line, and the mechanism of action relevant to possible therapeutic targeting.

Background: Small nuclear RNAs (snRNAs) are RNA components of the major and minor spliceosomes that play a core role in splice-site recognition and control of the splicing process. Variants in genes that produce snRNAs are increasingly recognised as major contributors to rare disorders, including neurodevelopmental disorders (NDD) and retinal dystrophies (collectively termed RNUopathies, a subset of spliceosomopathies). Clinical interpretation of variants in snRNAs is, however, challenging and existing guidance to support clinical variant classification does not adequately capture the unique features of snRNAs that necessitate a bespoke approach. Methods: We quantified the elevated background mutation rate in snRNA genes using de novo variants from 12,007 trios and assessed mutation density in 76,215 genome sequenced individuals in gnomAD. We convened a panel of clinical, research, and industry scientists with wide-ranging expertise in clinical variant interpretation and classification and expert knowledge in snRNA genes to draft and refine a guidance document. Results: We detail important considerations for variant classification in snRNA genes. These include: the difficulties of variant identification which requires genome or targeted sequencing approaches, the large number of gene paralogs with high sequence identity that complicate read mapping and variant calling, and historical inaccuracies in snRNA gene annotation. Further we show a ~50-fold increase in de novo mutation rate in snRNA genes compared to intergenic sequence and discuss the implications of this for variant classification. We provide a set of specific recommendations for classifying variants in snRNA genes. Finally, we introduce RNUdb, an interactive web-based tool to support snRNA variant annotation and classification. Conclusions: We provide the first guidance for clinical variant classification in snRNA genes and anticipate that this will support routine screening and analysis of snRNA genes in clinical genetic testing.

Purpose: Pathogenic variants in NFIX cause Marshall-Smith syndrome and Malan syndrome (MALNS). We identified a severe subtype of MALNS characterized by adolescent-onset musculoskeletal deterioration and investigated functional consequences of underlying variants. Methods: Clinical data were collected from seven individuals with pathogenic NFIX variants. Wild-type and mutated recombinant NFIX DNA-binding domains (DBDs) were evaluated using biochemical, structural, and DNA-binding assays. Results: Six individuals carrying R116W, R116P, K125E, or G147E NFIX substitutions developed progressive muscle wasting, markedly reduced body mass index, and rapidly progressive scoliosis after the typical childhood features of MALNS; two died from disease-related complications. A seventh individual with R116G did not develop this severe phenotype. Functional studies on recombinant NFIX DBDs showed complete or near-complete loss of DNA-binding activity for R116W, R116P, K125E, and G147E despite preserved protein folding, consistent with disrupted DNA recognition and a potential dominant-negative mechanism. In contrast, R116G exhibited a 7.7{degrees}C decrease in thermal stability, which may support haploinsufficiency mediated by protein degradation. Conclusion: Specific NFIX missense variants define a severe subtype of MALNS associated with progressive musculoskeletal deterioration. In vitro functional studies support variant-specific disruption of DNA binding, providing a mechanistic basis of genotype-phenotype correlations and informing prognosis, clinical surveillance, and therapy development.

Consanguinity increases the risk of autosomal recessive disorders and may result in the co-segregation of multiple pathogenic variants within the same family. Although most affected families are explained by a single genetic diagnosis, multilocus pathogenic variation can produce complex and overlapping clinical phenotypes. We investigated a consanguineous Pakistani family with three affected siblings, including dizygotic twins presenting with neurodevelopmental disorder and hearing loss, using detailed clinical evaluation, long-read whole-genome sequencing, bulk transcriptomics, protein profiling, and segregation analysis to determine the underlying molecular diagnoses. One sibling presented with isolated non-syndromic hearing loss, whereas the dizygotic twins exhibited severe neurodevelopmental impairment characterized by global developmental delay, spastic quadriplegic cerebral palsy, microcephaly, and white matter abnormalities. Long-read whole-genome sequencing identified a homozygous start-loss variant in HPDL (c.3G>C) in both twins, consistent with HPDL-related neurodevelopmental disorder with progressive spasticity and brain white matter abnormalities (NEDSWMA). In addition, a novel homozygous nonsense variant in EPS8 (c.1294C>T) was identified in one twin and the sibling with isolated hearing loss, explaining the auditory phenotype. Long-read transcriptomic analysis demonstrated absence of detectable EPS8 transcripts in both individuals homozygous for the nonsense variant, providing transcript-level evidence consistent with a loss-of-function mechanism. Genome-wide comprehensive proteomic profiling (SomaScan) identified distinct protein abundance profiles across family members, with the most pronounced alterations observed in the twins affected by HPDL-related neurodevelopmental disease, particularly the individual harboring pathogenic variants in both EPS8 and HPDL. This study expands the mutational spectrum of EPS8 and highlights the independent segregation of two autosomal recessive disorders within the complex consanguineous family, resulting in distinct and blended phenotypes.

Background Large-scale functional assays, including multiplex assays of variant effect, have substantial potential to resolve variants of uncertain significance (VUS), particularly for rare missense variants where clinical and population evidence are limited. The ClinGen assay-level clinical validation framework described by Brnich et al provided baseline guidance for the use of functional data for variant classification. However, clear consensus regarding construction of variant 'truthsets' by which to clinically validate functional data remains lacking. Methods CanVIG-UK developed consensus recommendations for truthset construction through an iterative national consultation process involving the CanVIG Steering Advisory Group (CStAG), wider CanVIG-UK membership, and engagement with international functional genomics experts. Consultation was based on previous analyses of 2,120 truthset constructions examining the impact of truthset composition on evidence point allocation within the ClinGen assay-level clinical validation framework. Results Across several consultations, CanVIG-UK established nine guiding principles and seven best-practice recommendations for assay-level clinical validation, using the assumed context of an assay for a cancer susceptibility gene where loss-of-function is the mechanism of pathogenicity. The principal recommendation stipulates, where assays are intended for use in interpretation of largely missense variants, the truthset used to validate should comprise only missense variants. Rather than mixtures of different variant types which may serve to over-estimate assay performance. Additional recommendations support option for relaxation of truthset stringency to improve power, augmentation of benign missense truthsets with systematically derived 'proxy-clinical' benign variants, independent clinical validation separate from assayist-defined validation, and careful evaluation of missense score distributions against that of protein-truncating and synonymous variants. Guidance is also provided for scenarios with limited pathogenic truthset availability and for assays reporting multiple deleterious zones or readouts. Conclusions The CanVIG-UK principles and recommendations for truthset construction upon the ClinGen assay-level clinical validation framework, while aiming to form a baseline for future discussion regarding other functional and disease contexts and helping to address the gap between publication of new data and routine clinical implementation.

Pathogenic mutations in the ABCA4 gene cause several inherited retinal diseases, particularly Stargardt disease (STGD1). However, many missense variants remain classified as variants of uncertain significance (VUS) due to inconclusive evidence regarding their pathogenic impact. The missense VUS span across all the domains of ABCA4, with the majority found in the larger extracellular domains (ECDs). The largest uncharacterized region of ABCA4 is located in ECD1, where limited structural information and inconsistent computational predictions hinder clinical interpretation of missense VUS in this region. Here, we integrated in silico analysis with in vitro functional assays to evaluate the pathogenicity of VUS in this region and improve their diagnostic classification. Missense VUS in the ECD1 uncharacterized region were curated from ClinVar. Six multiallelic sites were identified in the uncharacterized region and 13 missense VUS on these multiallelic sites were characterized using the integrated analysis. In the in silico platform, the pathogenicity of the VUS were predicted using multiple algorithms, and the structural effects of the variants were analyzed compared to the wild type. Recombinant variants were expressed in virus-like particles (VLPs), and protein expression, membrane localization, and ATPase activity were quantified relative to wild type to identify potential disease-causing variants. From the integrated analysis, variants with pronounced structural destabilization, impaired membrane trafficking, and reduced or absent N-retinylidene-phosphatidylethanolamine (NRPE) substrate stimulated ATPase activities were identified as potentially deleterious. Notably, VUS at p.H193P and p.I214N showed loss of function, with p.I214N reflecting selectively impaired membrane targeting and p.H193P reflecting combined expression and trafficking defects. Additionally, NRPE-stimulated ATPase activities were impaired in VUS, p.V195L, p.V195I, p.D197H, p.I214F and p.N269S. Overall structural destabilization interfered with the NRPE-stimulated ATPase activities of p.N269S, while the lack of NRPE-stimulated ATPase activities of p.D197H, p.V195L, p.V195I and p.I214F are thought to be due to impaired NRPE interactions with ABCA4. All the VUS at p.R140, p.H193Y, p.D197N and p.N269H showed both the basal and NRPE-stimulated ATPase activities but less than that of the wild type, displaying a mild functional deficit. Together, these findings demonstrated that certain VUS within the unresolved ECD1 region disrupt ABCA4 stability and function, supporting their contribution to disease pathogenesis. This integrative approach highlights key residues likely to be pathogenic and advances the interpretation of VUS in inherited retinal disorders.

BackgroundAcrodysostosis type 2 (ACRDYS2) is a rare autosomal dominant disease characterized by skeletal defects and cognitive deficit, with clinical symptoms observed in multiple other tissues including the skin. It is caused by mutations in a phosphodiesterase, PDE4D, a key regulator of cAMP/PKA (cyclic adenosine monophosphate / protein kinase A) signalling. Despite its well-defined genetic causes, the molecular mechanisms underlying the disease remain poorly understood, with studies based largely on engineered cellular models reaching conflicting interpretations. MethodsTo investigate how endogenous dynamics are affected by PDE4D mutations in unmanipulated cells, we studied PDE4D transcript and protein expression, activity and downstream signalling in native dermal fibroblast from ACRDYS2 patients and healthy controls. ResultsSignificant reduction in total PDE4D expression in patient cells was observed both at the transcript and protein level, with marked decreases in the long isoforms PDE4D4 and PDE4D7; a reduction in PDE4D9 mRNA was also observed. PDE4D enzymatic activity was reduced in ACRDYS2 fibroblasts, though total PDE activity was largely preserved. Reduced PDE4D expression was associated with an increase in the phosphorylated form of the cAMP-responsive transcription factor CREB and elevated PRKAR1A (PKA type 1 regulatory subunit alpha) transcript levels, suggesting altered downstream signalling. Interestingly, expression of the related phosphodiesterase family member PDE4B was increased, consistent with a compensatory response to reduced PDE4D function. ConclusionsThis is the first study demonstrating reduced PDE4D expression and isoform-specific dysregulation in native ACRDYS2 cells. Together, our results support a model in which reduction in PDE4D activity and compensatory changes in other PDE4 family members contribute to the molecular pathology of ACRDYS2, providing new insights into the molecular mechanisms underlying this disorder.

Distinguishing loss-of-function (LOF) from gain-of-function (GOF) effects of missense variants is fundamental to understanding disease mechanisms and guiding therapeutic strategy, yet no large-scale, expert-curated benchmark has been publicly available for this task. Here we present GLOF (Gain and Loss Of Function), a dataset of 112,399 missense variants across 2,809 human genes, each classified as LOF, GOF, or neutral by board-certified clinical geneticists following ACMG guidelines. Pathogenic variants were sourced from ClinVar and annotated with their functional mechanism based on published functional studies, phenotype correlations, and established gene-disease relationships. Neutral variants were drawn from gnomAD v3.1 and validated against v4.1 using stringent population frequency filters. The dataset spans diverse protein families, includes 97 genes with bidirectional mechanisms (containing both LOF and GOF variants), and has been validated against well-characterized variants in the literature. GLOF is publicly available on Kaggle (https://www.kaggle.com/datasets/maricatovictor/loss-and-gain-of-function-variants) and Hugging Face (https://huggingface.co/datasets/victormaricato/glof), and provides a standardized resource for developing and benchmarking computational methods that predict variant functional mechanisms.

Purpose: To identify transcript-level variants in crystallin genes in paediatric patients with unilateral cataracts. Methods: Anterior capsulorhexis (n=12) from patients underwent surgical management of congenital unilateral cataracts was collected. Total RNA was isolated from lens epithelial cells, and complementary DNA (cDNA) was synthesized. Full-length RNA transcripts of 10 lens-specific crystallin genes were PCR-amplified and analysed via Sanger sequencing. Identified transcript variants were further validated using genomic DNA (gDNA) through Sanger sequencing. In addition, the full-length (~7,535 bp) CRYBA1 genomic region was sequenced using Oxford Nanopore Technology. Results: Aberrant low molecular weight (LMW) amplicons (~370 bp) of the CRYBA1 transcript were identified in three patients presented with unilateral cataract. Of 3 patients, 2 had persistent fetal vasculature (PFV) and 1 had pre-existing posterior capsular defect (PPCD). Sanger sequencing revealed a precise loss of exons 2 to 4 in the CRYBA1 RNA transcript. No coding, splice-site, or large deletion variants were detected in the genomic DNA of the patients or their parents. In silico analysis predicted two possible truncated proteins arising from these alternatively spliced transcripts: one comprising the first 11 amino acids of the N-terminal region with a loss of all Greek key motifs, and another comprising 90 amino acids encoded by exons 5 and 6, initiated from an alternative start codon in exon 5, and loss of Greek key motifs 1 & 2. Conclusion: The precise skipping of exons 2 to 4, consistent with canonical splicing signals (5-prime-GU...AG-3-prime), in the absence of genomic alterations, suggests the presence of alternatively spliced (AS) CRYBA1 transcripts in human lenses. This is the first report documenting AS-CRYBA1 transcripts in association with childhood cataracts with PFV and PPCD.

Rare diseases (RDs) remain a major diagnostic challenge. Genetic and phenotypic heterogeneity, incomplete knowledge of disease mechanisms, and limitations in variant clinical interpretation leave many patients without a molecular diagnosis. Meanwhile, the growing volume of genomic data generated in clinical practice offers an opportunity to develop data-driven methodologies for exploring disease mechanisms and improving the reanalysis of unsolved cases. We aggregated real-world genomic data from 11,084 unrelated patients with suspected RD. Patients were clinically classified into 122 diseases. We built a multi-disease genomic variant frequency database (FJD-DB), which enabled the development of variant and gene-disease association scores by means of case-control subcohort comparisons across 32 disease groups. Functional enrichment analyses were then used to highlight disease-associated protein domains, pathways, biological processes, and phenotypes. Finally, the resulting knowledge was integrated into a data-driven framework for the guided reanalysis of unsolved RD patients applied to Inherited Retinal Dystrophies (IRD) patients as first use case. FJD-DB contained more than 45 million unique variants, including ~185,000 potentially pathogenic variants. Disease-specific analyses identified disease-associated pathogenic variants and highlighted both established and candidate disease genes. We detected 179 significantly enriched protein domains across 23 diseases, 124 Human Phenotype Ontology terms across 13 diseases, 79 Reactome pathways across 10 diseases, and 72 Gene Ontology biological processes across 8 diseases, revealing highly disease-specific functional signatures. Integration of disease-specific variant, gene, and functional association signals enabled the development of a data-driven framework for guided reanalysis of unsolved RD cases. Applied to more than 1,100 unsolved IRD cases, the framework generated clinically relevant findings in 26 patients, including four molecular diagnoses, seven candidate diagnoses, and 15 cases upgraded from non-informative findings to variants of uncertain significance. Aggregated real-world genomic data can be leveraged to identify disease-associated molecular signals generating novel biological hypotheses. A unified analytical framework provides a scalable strategy for knowledge discovery and guided reanalysis, facilitating the identification of overlooked and potentially novel genetic causes of RDs.

Accurate interpretation of rare germline variants remains a major challenge in developmental disorders (DD). Somatic mutation data represent a largely untapped source of evidence for germline variant classi-fication. Identical or nearby mutations that drive positive selection when present in somatic tissues can cause developmental disorders when present in the germline. We integrated somatic mutation data from the Catalogue Of Somatic Mutations In Cancer (COSMIC), and healthy tissues (sperm and buccal epithelium) with germline variant datasets from ClinVar and large studies of de novo mutations in DD patients. Across 970 dominant DD genes, 195 have evidence of somatic selection, with a majority demonstrating concordant mechanisms between germline and somatic contexts. We benchmark the ability of somatic data to discriminate pathogenic from benign germline missense variation across dominant DD genes, identifying 145 genes in which somatic data are informative. The strongest utility is in altered-function genes where germline and somatic mechanisms are concordant, for example the RASopathy genes. In these genes, codon-level aggregation of somatic missense counts yields predictive performance comparable to computational predictors or MAVE assays (AUC-ROC 0.895 for somatic data, versus 0.893 for REVEL). Combining somatic features with computational scores improves discrimination further. Using likelihood ratios, we map COSMIC missense codon count thresholds onto American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP)-style evidence strengths, showing that somatic data can reach strong levels of evidence in germline variant interpretation in DD and enable reclassification of variants of uncertain significance. Together, these results establish somatic mutation data as a scalable and clinically actionable evidence source for germline variant interpretation in select DD genes. Graphical abstract(Generated using FigureLabs) O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=104 SRC="FIGDIR/small/732808v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@150bec9org.highwire.dtl.DTLVardef@1dacf5org.highwire.dtl.DTLVardef@46121dorg.highwire.dtl.DTLVardef@4f5c38_HPS_FORMAT_FIGEXP M_FIG C_FIG

Pathogenic variants in the myocilin (MYOC) gene are the most common cause of Mendelian open-angle glaucoma. In 2022, the Clinical Genome Resource (ClinGen) Glaucoma Variant Curation Expert Panel (VCEP) published rule specifications for MYOC variant interpretation, including a pilot study of 81 variants. Here, we present the results of curating 271 MYOC variants reported in people with open-angle glaucoma using updated specification rules. Of all the variants, 11 were classified as benign (B), 45 as likely benign (LB), 166 as variants of uncertain significance (VUS), 35 as likely pathogenic (LP), and 14 as pathogenic (P). All LP/P variants were located within the conserved olfactomedin domain encoded by exon 3. The updated variant curation guidelines from the Glaucoma VCEP increased the number of clinically definitive classifications from 28% (74/265) to 39% (105/271), with 95% (41/43) of reclassified variants moving to greater clinical relevance. Functional evidence was lacking for 93% (154/166) of VUS. Additional functional evidence could further enhance classification by halving (85/166) the proportion of those classified as VUS. These findings highlight the role of rule calibration and rigorous functional evidence assessment toward improving variant classification with clinical utility for patients.

Evaluating the impact of genomic variation is essential for identifying underlying mechanistic causes of human diseases. The spectrum of neurodevelopmental disorders is driven by diverse genetic alterations with genes like SMARCA4 being prototypical examples. There have been significant hurdles to implementing the protein-specific and mechanism-informed variation effect predictors that are anticipated to have the highest yield of mechanistic information. Yet, there is a pressing need, for example, within SMARCA4 where 98% of the 2780 reported variants lack a disposition and remain of uncertain significance (VUS). Further, the field has yet to identify each variants specific molecular mechanism, which will inform targeted therapeutic development strategies. In this study we developed a mechanistic structure-informed helicase-specific variant effect predictor by leveraging diverse information with state-specific calculations. Our approach has 100% recall of pathogenic variants while classifying 87.23% of VUS into damaging (55.74%, n=262) versus tolerated effects (31.49%, n=148), including those with conflicting interpretations. This analysis reveals significant enrichment of integrated functional metrics, such as conservation and solvent exposure, that parallel allele frequences in health populations, and emphasizes the robustness of the method. Thus, we have demonstrated a novel approach for the development of mechanism-informed protein-specific interpretation of human genetic information.

Targeted precision therapies are increasingly used in the treatment of individuals with vascular anomalies (VAs). This increases the need for rapid, accurate and inexpensive genetic diagnosis. Droplet digital polymerase chain reaction (ddPCR) is an alternative to next-generation sequencing (NGS), permitting rapid, highly sensitive interrogation of recurrent pathogenic mosaic variants. We examined the feasibility of ddPCR as a primary diagnostic tool in a large cohort of individuals with VAs. Lesional tissue was collected for ddPCR of up to 46 recurrent pathogenic variants across 16 genes associated with VAs. Specimens were assessed on a subset of assays for each individual based on clinical phenotype. Most individuals who had negative ddPCR results went on to high-depth gene panel or deep exome NGS, or Sanger sequencing. Here we report the phenotypic and molecular findings for 78 newly recruited and tested individuals in addition to the 60 individuals already reported from our cohort. The overall diagnostic yield for our cohort when combined with individuals previously reported was 104/138 (75%). Of 138 individuals tested, recurrent pathogenic variants were detected in 71 (51%) on ddPCR. Variants were most frequently identified in PIK3CA (n=28), TEK (n=18), GNAQ (n=12), or MAP2K1 (n=7). In a further 33 individuals, pathogenic variants were identified on NGS or Sanger sequencing. Our findings indicate that ddPCR is an efficient method achieving a high diagnostic yield in our cohort when used prior to sequencing.

Founder mutations are variants that arose in a single ancestor and became enriched in a descendant population through a bottleneck and endogamy. Identification of pathogenic founder mutations has facilitated efficient targeted screening. More broadly, even without confirmed founder status, identifying pathogenic variants that are enriched within specific populations reveals population-specific disease burden. However, many such variants remain hidden in plain sight within existing datasets. To address this gap, we developed FIND (Founder candidates hidden IN Data), a web tool that identifies pathogenic, likely pathogenic, and predicted loss-of-function variants in gnomAD with frequencies >0.00008 in one ancestry group and at least tenfold higher than in all others (after zeroing populations with four or fewer observed alleles). Testing FIND on the genes FLNC, TMEM127, MYH7, and BRCA2 confirmed its utility and functionality by identifying nine well-known founder mutations and seven candidate founders. Candidates enriched in African American and admixed American populations were validated with the All of Us database, highlighting the utility of this approach for populations historically underrepresented in genetic studies. Source code is freely available at https://github.com/aacoder105/FIND under an MIT license, with a web interface at https://ethnic-variant-mutation-finder.onrender.com/.

Background: Clear guidance is lacking regarding how 'truthset' variants should be used for clinical validation of functional assays, namely determining the allocatable evidence points (EPs) towards clinical classification. It is argued that assays should be validated using truthsets of missense variants, as this is the variant type for which classification is most impacted by functional data. EPs will be influenced by both the number of available 'truthset' variants and their concordance with assay readouts. Methods: We first reviewed 112 sets of ClinGen gene-specific classification specifications (CSPECs) to assess methodologies they applied for truthset assembly and clinical validation of assays. We then proposed differing rules regarding variant type and stringency of classification by which truthsets might be assembled using ClinVar-extracted classifications. We then examined augmentation of ClinVar-classified truthsets with 'proxy-clinical' benign-classified missense variants systematically assembled applying ACMG/AMP rules (of differing stringencies). In total, these constituted 70 basic approaches to ClinVar-based truthset assembly, which we applied to VHL, BRCA1, BRCA2 and RAD51C. We additionally analysed the impact on the size of the truthsets of changing the specified phenotypes against which ClinVar classification had been submitted. We then applied these truthsets to quantify concordance and allocatable EPs for five large-scale multiplexed functional assays for VHL, BRCA1, BRCA2, and RAD51C. Results The EPs from clinical validation of each assay varied widely according to which truthset was used across 2,120 permutations of gene-truthset-assay combinations. For example, sequentially applying 700 different ClinVar-based truthsets to 2,268 VHL assay variant readouts (70 basic ClinVar-based approaches, augmented by examining 5 different phenotypes for each basic approach, and separate validation against two defined deleterious zones), the evidence strength allocatable for pathogenicity ranged from nil to strong evidence (0.0 to 5.6 EPs); for benignity it ranged from supporting to strong evidence (-1.5 to -6.4 EPs). Clinical validation using truthsets comprising just ClinVar-classified missense variants typically resulted in lower EPs than truthsets comprising protein truncating (PTV) and synonymous variants; this was more due to paucity of ClinVar-classified missense truthset variants than poorer concordance. Augmentation with larger 'proxy-clinical' benign-classified missense truthsets typically improved evidence allocatable for pathogenicity, with improved power negating modest reduction in concordance. Conclusions EPs can be improved by augmentation with systematically-generated 'proxy-clinical' benign-classified missense variants and/or reduction of truthset stringency. Explicit prescriptive clinical guidance is urgently required to improve consistency in clinical validation of functional assays and consequent evidence application for clinical variant classification.

Genome sequencing of the heterogeneous primary mitochondrial disorders (PMD) frequently reveals variants of uncertain significance that require functional tests for diagnosis, and does not identify variants in all patients. We analyzed mitochondrial enzyme assays, blue native polyacrylamide gel electrophoresis (BN-PAGE) with in-gel activity staining, complex I assembly blot, and select protein abundances in fibroblasts of a case series of 204 PMD patients divided into functional classes, in comparison to 51 controls and 53 differential diagnostic conditions. Overall, sensitivity and specificity for respiratory chain enzyme assays were 46% and 93% respectively, for BN-PAGE 40% and 98%, for complex I assembly assay 49% and 99%. The overall sensitivity of all tests was 76%, specificity 93%, with positive predictive value 96% and negative predictive value 67%. Categories with high sensitivity were isolated complex deficiencies, nuclear DNA-encoded mitochondrial protein synthesis defects, co-factor defects, and mitochondrial amino-acyl-tRNA synthetase conditions when aided by protein abundance. Mitochondrial DNA mutations and maintenance disorders showed poor sensitivities. Secondary dysfunctions were rare. A complete battery of functional tests showed strong diagnostic clinical utility in fibroblasts.

BackgroundMYORG (myogenesis-regulating glycosidase) and STRADB (STE20-related kinase adapter protein beta) were previously identified as activity-mediated skeletal muscle genes with potential roles in frailty and sarcopenia. We hypothesized that, if these genes are sustained by neuromuscular contractile activity, their expression should be consistently downregulated in muscular dystrophies, conditions defined by progressive muscle degeneration and secondary functional disuse. MethodsWe performed a systematic cross-dataset transcriptomic analysis of five publicly available GEO microarray datasets of human skeletal muscle. Discovery analysis was conducted in GSE3307 (Affymetrix HG-U133A/B; samples spanning DMD, LGMD2A/B/I, BMD, FSHD, JDM, ALS, AQM versus healthy controls). Independent external validation was performed in GSE38417 (HG-U133 Plus 2.0, DMD; n=16/6), GSE11681 (HG-U133A/B, LGMD2A; n=8-10/9-10), GSE465 (HG-U95Av2/B/C, multi-disease), and GSE1007 (HG-U95B/C/E, DMD; n=10-11/11). Raw CEL files underwent array-level quality assessment using NUSE and RLE diagnostics prior to normalization. Seven poor-quality arrays were excluded (none from Control, DMD, or LGMD groups). Remaining arrays were processed by robust multi-array average (RMA) normalization, and differential expression was assessed by limma with Benjamini-Hochberg FDR correction. ResultsMYORG was significantly downregulated in DMD (log2 fold-change [logFC] = -0.93, adj.P<0.001), LGMD2A (logFC = -0.82, adj.P<0.01), LGMD2B (logFC = -1.01, adj.P<0.01), and LGMD2I (logFC = -1.03, adj.P<0.01) in GSE3307. STRADB was significantly reduced in DMD (logFC = -0.33, adj.P<0.05) and showed a near-significant trend in LGMD2I (logFC = - 0.42, adj.P = 0.061). MYORG downregulation in DMD was independently replicated in GSE38417 (logFC = -1.40, adj.P<0.001) and GSE1007 (logFC = -0.80, adj.P<0.001). STRADB was also significantly downregulated in GSE38417 DMD (logFC = -0.45, adj.P<0.001). Deoxygalactonojirimycin, an iminosugar and an FDA/EMA-approved pharmacological chaperone (migalastat/Galafold) for Fabry disease, has been reported to be a specific molecular interactor that stabilizes MYORG protein in skeletal muscle. ConclusionsThis multi-dataset study further supports the role of MYORG and STRADB as activity-sensitive muscle genes that are robustly downregulated in DMD and LGMD. The pharmacological interaction between migalastat and MYORG provides a mechanistically grounded rationale for investigating this approved agent as an adjunct therapy in muscular dystrophies, in combination with the existing standard of care. This also supports active investigation of iminosugar analogs to target MYORG as potential therapeutics for improving skeletal muscle function in dystrophies, frailty, and sarcopenia.

Objective Beckwith-Wiedemann spectrum (BWSp) is an overgrowth and cancer predisposition disorder caused by genetic and epigenetic alterations of chromosome 11p15. The 2018 international consensus produced a clinical scoring system to capture the phenotypic variability of BWSp and guide genetic testing and clinical management, including tumor screening, in patients without molecular confirmation. In this study, we evaluated BWSp predictors to identify the most informative features. Methods Supervised machine learning analyzed 25 phenotypic features in 555 patients with BWSp and 150 controls. Logistic regression, combined with a purposeful stepwise selection algorithm, identified a subset of features that can accurately classify subjects. Model performance was evaluated in a testing set and validated externally. Results The final model included six predictors: macroglossia, lateralized overgrowth, midface flattening, hepatomegaly, omphalocele, and developmental delay. Developmental delay was the only negative predictor; macroglossia (OR 46.10) and lateralized overgrowth (OR 27.87) were the strongest predictors. The proposed model and 2018 system did not differ in classification performance for testing (P = .39) or external (P = .15) sets. Conclusion A simplified diagnostic model, driven by macroglossia and lateralized overgrowth, differentiates between patients with BWSp and controls with performance comparable to the 2018 system. And may help physicians prioritize BWSp evaluation.

Germline mutations in PTPN11 cause Noonan syndrome (NS) and NS with multiple lentigines (NSML), yet how specific variants drive divergent clinical outcomes through distinct signaling and developmental mechanisms remains unclear. We find that germline and somatic mutations converge on N-SH2 and PTP domains but diverge at residue-level hotspots, reflecting distinct selective pressures. Clinical stratification of 18 pediatric patients reveals four distinct phenotypic classes including (i) the NSML-associated c.1403C>T (T468M) variant, characterized by lentigines, moderate growth impairment, and distinctive facial features; (ii) variants including the VUS c.1282G>A (V428M) and c.1432A>G (I478V), which were associated with cognitive deficits and variable growth impairment; (iii) c.1471C>A (P491T) and c.1472C>T (P491L), predominantly affecting cardiac and growth phenotypes with limited neurocognitive features; and (iv) a severe, multisystem class comprising c.172A>G (N58D), c.178G>A (G60S), c.844A>G (I282V), c.922A>G (N308D), and c.923A>G (N308S), spanning cardiac, growth, cognitive, and craniofacial abnormalities. Biochemical profiling in HEK293T cells revealed that PTPN11 variants stratify beyond simple gain/loss-of-function dichotomies into strong ERK-dependent hyperactivation, moderate ERK activation with variable protein stability and the paradoxical c.1282G>A variant, which did not increase ERK phosphorylation. In vivo, this variant drove excessive neural crest cell migration in chick embryos, suggesting that its effects on NCC migration may involve ERK-independent mechanisms or context-dependent signaling not captured by steady-state assays. ERK activation did not strictly correlate with clinical severity, yet these functional differences were associated with distinct growth, cardiac, pigmentation, and neurodevelopmental outcomes. Our data suggest lineage-specific sensitivity to SHP2 dosage, with dorsal root ganglia neurons appearing more vulnerable to reduced SHP2 stability than melanocyte precursors. Although direct correlations between specific signaling defects and individual clinical features remain complex, our findings provide a refined framework for PTPN11 variant classification, and reveal unexpected SHP2 functions in neural crest development.