An HNRNPK-specific DNA methylation signature makes sense of missense variants and expands the phenotypic spectrum of Au-Kline syndrome

A Novel Intronic Variant in the KH3 Domain of HNRNPK Leads to a Mild Form of Au-Kline Syndrome

Despite the massive adoption of sequencing technologies, disease-specific diagnosis remains challenging, particularly for genes with highly homologous pseudogenes like HNRNPK. Pathogenic HNRNPK variants cause Au-Kline syndrome (AKS), a neurodevelopmental disorder with malformations and distinctive facial features. We validated a novel de novo HNRNPK intronic variant (c.1192-3 C>A, p.Leu398ValfsTer21) in a patient previously misdiagnosed with Kabuki Syndrome (KS). By combining sequencing, in vitro splicing assays, molecular modelling, and protein function analysis, we characterised the molecular defect. A unique DNA methylation (DNAm) signature was recently identified in AKS, with missense variants showing an intermediate DNAm pattern, suggesting an epi-genotype-phenotype correlation linked to milder clinical features. The DNAm signature is a valuable tool for variant interpretation, especially in unclear AKS cases. We demonstrate that two independent approaches-functional characterisation and DNAm evaluation-confirmed a partial loss of HNRNPK function and validated an AKS diagnosis with a mild phenotype. Our findings highlight that a multidisciplinary approach integrating genomic and epigenomic analyses with functional studies and clinical assessment significantly improves rare disease diagnosis.

Artificial intelligence-driven genotype-epigenotype-phenotype approaches to resolve challenges in syndrome diagnostics

BACKGROUND

Decisions to split two or more phenotypic manifestations related to genetic variations within the same gene can be challenging, especially during the early stages of syndrome discovery. Genotype-based diagnostics with artificial intelligence (AI)-driven approaches using next-generation phenotyping (NGP) and DNA methylation (DNAm) can be utilized to expedite syndrome delineation within a single gene.

METHODS

We utilized an expanded cohort of 56 patients (22 previously unpublished individuals) with truncating variants in the MN1 gene and attempted different methods to assess plausible strategies to objectively delineate phenotypic differences between the C-Terminal Truncation (CTT) and N-Terminal Truncation (NTT) groups. This involved transcriptomics analysis on available patient fibroblast samples and AI-assisted approaches, including a new statistical method of GestaltMatcher on facial photos and blood DNAm analysis using a support vector machine (SVM) model.

FINDINGS

RNA-seq analysis was unable to show a significant difference in transcript expression despite our previous hypothesis that NTT variants would induce nonsense mediated decay. DNAm analysis on nine blood DNA samples revealed an episignature for the CTT group. In parallel, the new statistical method of GestaltMatcher objectively distinguished the CTT and NTT groups with a low requirement for cohort number. Validation of this approach was performed on syndromes with known DNAm signatures of SRCAP, SMARCA2 and ADNP to demonstrate the effectiveness of this approach.

INTERPRETATION

We demonstrate the potential of using AI-based technologies to leverage genotype, phenotype and epigenetics data in facilitating splitting decisions in diagnosis of syndromes with minimal sample requirement.

FUNDING

The specific funding of this article is provided in the acknowledgements section.

Recruitment of chromatin remodelers by XIST B-repeat region is variably dependent on HNRNPK

X-chromosome inactivation is triggered by the long non-coding RNA XIST, whose structure is characterized by tandem repeats that modularly recruit different proteins and chromatin remodelers. Previously, we reported that the addition of the mouse PID region to a transgene with human repeat regions A, F and E (miniXIST; 5.1 kb) enabled binding of HNRNPK and also enabled the induction of silencing and recruitment of H3K27me3, UbH2A and H4K20me1, but only partially. As the 680 bp PID region enabled so many features of inactivation, we hypothesized that augmenting the PID with more mouse or human sequences rich in CCC motifs would allow us to design a short transgene which was as effective as Full XIST. Three new transgenes using the A, F and E human domains as a backbone were tested for ability to induce silencing and heterochromatic mark recruitment. The all human-derived BhB-BhB transgene (4.9 kb) was as good as our previous miniXIST, suggesting that these domains are the human equivalent of the mouse PID region. A PID-PID transgene (5.8 kb) was not statistically different from Full XIST and could be potentially used for chromosome therapy. Adding BhB to PID (BhB-PID, 5.4 kb) had an intermediate efficacy compared to the other two transgenes, suggesting that the most important component for silencing and heterochromatic mark recruitment is the number of CCC motifs, not the species of origin. Finally, we created a heterozygous HNRNPK deletion and observed a disproportionate impact on HNRNPK and UbH2A recruitment to XIST, reflecting complex roles for the PID and HNRNPK in X-chromosome inactivation.

Validation of a hypomorphic variant in CDK13 as the cause of CHDFIDD with autosomal recessive inheritance through determination of an episignature

Autosomal dominant CDK13-related disease is characterized by congenital heart defects, dysmorphic facial features, and intellectual developmental disorder (CHDFIDD). Heterozygous pathogenic variants, particularly missense variants in the kinase domain, have previously been described as disease causing. Using the determination of a methylation pattern and comparison with an established episignature, we reveal the first hypomorphic variant in the kinase domain of CDK13, leading to a never before described autosomal recessive form of CHDFIDD in a boy with characteristic features. This highlights the utility of episignatures in variant interpretation, as well as a potential novel diagnostic approach in unsolved cases or for disease prognosis.

Clinical and molecular characteristics of Korean patients with Kabuki syndrome

INTRODUCTION

Kabuki syndrome (KS) is a rare disorder characterized by typical facial features, skeletal anomalies, fetal fingertip pad persistence, postnatal growth retardation, and intellectual disabilities. Heterozygous variants of the KMT2D and KDM6A genes are major genetic causes of KS. This study aimed to report the clinical and genetic characteristics of KS.

METHODS

This study included 28 Korean patients (14 boys and 14 girls) with KS through molecular genetic testing, including direct Sanger sequencing, whole-exome sequencing, or whole-genome sequencing.

RESULTS

The median age at clinical diagnosis was 18.5 months (IQR 7-58 months), and the median follow-up duration was 80.5 months (IQR 48-112 months). Molecular genetic testing identified different pathogenic variants of the KMT2D (n = 23) and KDM6A (n = 3) genes, including 15 novel variants. Patients showed typical facial features (100%), such as long palpebral fissure and eversion of the lower eyelid; intellectual disability/developmental delay (96%); short stature (79%); and congenital cardiac anomalies (75%). Although 71% experienced failure to thrive in infancy, 54% of patients showed a tendency toward overweight/obesity in early childhood. Patients with KDM6A variants demonstrated severe genotype-phenotype correlation.

CONCLUSION

This study enhances the understanding of the clinical and genetic characteristics of KS.

Pathogenic variants in KMT2C result in a neurodevelopmental disorder distinct from Kleefstra and Kabuki syndromes

Trithorax-related H3K4 methyltransferases, KMT2C and KMT2D, are critical epigenetic modifiers. Haploinsufficiency of KMT2C was only recently recognized as a cause of neurodevelopmental disorder (NDD), so the clinical and molecular spectrums of the KMT2C-related NDD (now designated as Kleefstra syndrome 2) are largely unknown. We ascertained 98 individuals with rare KMT2C variants, including 75 with protein-truncating variants (PTVs). Notably, ∼15% of KMT2C PTVs were inherited. Although the most highly expressed KMT2C transcript consists of only the last four exons, pathogenic PTVs were found in almost all the exons of this large gene. KMT2C variant interpretation can be challenging due to segmental duplications and clonal hematopoesis-induced artifacts. Using samples from 27 affected individuals, divided into discovery and validation cohorts, we generated a moderate strength disorder-specific KMT2C DNA methylation (DNAm) signature and demonstrate its utility in classifying non-truncating variants. Based on 81 individuals with pathogenic/likely pathogenic variants, we demonstrate that the KMT2C-related NDD is characterized by developmental delay, intellectual disability, behavioral and psychiatric problems, hypotonia, seizures, short stature, and other comorbidities. The facial module of PhenoScore, applied to photographs of 34 affected individuals, reveals that the KMT2C-related facial gestalt is significantly different from the general NDD population. Finally, using PhenoScore and DNAm signatures, we demonstrate that the KMT2C-related NDD is clinically and epigenetically distinct from Kleefstra and Kabuki syndromes. Overall, we define the clinical features, molecular spectrum, and DNAm signature of the KMT2C-related NDD and demonstrate they are distinct from Kleefstra and Kabuki syndromes highlighting the need to rename this condition.

Diagnostic utility and reporting recommendations for clinical DNA methylation episignature testing in genetically undiagnosed rare diseases

PURPOSE

This study aims to assess the diagnostic utility and provide reporting recommendations for clinical DNA methylation episignature testing based on the cohort of patients tested through the EpiSign Clinical Testing Network.

METHODS

The EpiSign assay utilized unsupervised clustering techniques and a support vector machine-based classification algorithm to compare each patient's genome-wide DNA methylation profile with the EpiSign Knowledge Database, yielding the result that was reported. An international working group, representing distinct EpiSign Clinical Testing Network health jurisdictions, collaborated to establish recommendations for interpretation and reporting of episignature testing.

RESULTS

Among 2399 cases analyzed, 1667 cases underwent a comprehensive screen of validated episignatures, imprinting, and promoter regions, resulting in 18.7% (312/1667) positive reports. The remaining 732 referrals underwent targeted episignature analysis for assessment of sequence or copy-number variants (CNVs) of uncertain significance or for assessment of clinical diagnoses without confirmed molecular findings, and 32.4% (237/732) were positive. Cases with detailed clinical information were highlighted to describe various utility scenarios for episignature testing.

CONCLUSION

Clinical DNA methylation testing including episignatures, imprinting, and promoter analysis provided by an integrated network of clinical laboratories enables test standardization and demonstrates significant diagnostic yield and clinical utility beyond DNA sequence analysis in rare diseases.

DNA methylation signatures for chromatinopathies: current challenges and future applications

Pathogenic variants in genes that encode epigenetic regulators are the cause for more than 100 rare neurodevelopmental syndromes also termed "chromatinopathies". DNA methylation signatures, syndrome-specific patterns of DNA methylation alterations, serve as both a research avenue for elucidating disease pathophysiology and a clinical diagnostic tool. The latter is well established, especially for the classification of variants of uncertain significance (VUS). In this perspective, we describe the seminal DNA methylation signature research in chromatinopathies; the complex relationships between genotype, phenotype and DNA methylation, and the future applications of DNA methylation signatures.

Loss of function in NSD2 causes DNA methylation signature similar to that in Wolf-Hirschhorn syndrome

Purpose

Wolf-Hirschhorn syndrome (WHS), a contiguous gene syndrome caused by heterozygous deletions of the distal short arm of chromosome 4 that includes NSD2, reportedly causes specific DNA methylation signatures in peripheral blood cells. However, the genomic loci responsible for these signatures have not been elucidated. The present study aims to define the loci underlying WHS-related DNA methylation signatures and explore the role of NSD2 in these signatures.

Methods

We conducted genome-wide methylation analysis of individuals with WHS or NSD2 variants using an array method. We studied genome-edited knockin mice and induced pluripotent stem cells to explore the function of NSD2 variants.

Results

Three undiagnosed cases with NSD2 variants showed WHS-related DNA methylation signatures. In patient-derived induced pluripotent stem cells and genome-edited knockin mice, these variants cause NSD2 loss of function, respectively. The p.Pro905Leu variant caused decreased Nsd2 protein levels and altered histone H3-lysine 36 dimethylation levels similarly to what was observed in Nsd2 knockout mice. Nsd2 knockout and p.Pro905Leu knockin mice exhibited common DNA methylation changes.

Conclusion

These results revealed that WHS-related DNA methylation signatures are dependent on NSD2 dysfunction and could be useful in identifying NSD2 variants of uncertain significance.

A new blood DNA methylation signature for Koolen-de Vries syndrome: Classification of missense KANSL1 variants and comparison to fibroblast cells

Pathogenic variants in KANSL1 and 17q21.31 microdeletions are causative of Koolen-de Vries syndrome (KdVS), a neurodevelopmental syndrome with characteristic facial dysmorphia. Our previous work has shown that syndromic conditions caused by pathogenic variants in epigenetic regulatory genes have identifiable patterns of DNA methylation (DNAm) change: DNAm signatures or episignatures. Given the role of KANSL1 in histone acetylation, we tested whether variants underlying KdVS are associated with a DNAm signature. We profiled whole-blood DNAm for 13 individuals with KANSL1 variants, four individuals with 17q21.31 microdeletions, and 21 typically developing individuals, using Illumina's Infinium EPIC array. In this study, we identified a robust DNAm signature of 456 significant CpG sites in 8 individuals with KdVS, a pattern independently validated in an additional 7 individuals with KdVS. We also demonstrate the diagnostic utility of the signature and classify two KANSL1 VUS as well as four variants in individuals with atypical clinical presentation. Lastly, we investigated tissue-specific DNAm changes in fibroblast cells from individuals with KdVS. Collectively, our findings contribute to the understanding of the epigenetic landscape related to KdVS and aid in the diagnosis and classification of variants in this structurally complex genomic region.

Biallelic variants in RBM42 cause a multisystem disorder with neurological, facial, cardiac, and musculoskeletal involvement

Here, we report a previously unrecognized syndromic neurodevelopmental disorder associated with biallelic loss-of-function variants in the RBM42 gene. The patient is a 2-year-old female with severe central nervous system (CNS) abnormalities, hypotonia, hearing loss, congenital heart defects, and dysmorphic facial features. Familial whole-exome sequencing (WES) reveals that the patient has two compound heterozygous variants, c.304C>T (p.R102*) and c.1312G>A (p.A438T), in the RBM42 gene which encodes an integral component of splicing complex in the RNA-binding motif protein family. The p.A438T variant is in the RRM domain which impairs RBM42 protein stability in vivo. Additionally, p.A438T disrupts the interaction of RBM42 with hnRNP K, which is the causative gene for Au-Kline syndrome with overlapping disease characteristics seen in the index patient. The human R102* or A438T mutant protein failed to fully rescue the growth defects of RBM42 ortholog knockout ΔFgRbp1 in Fusarium while it was rescued by the wild-type (WT) human RBM42. A mouse model carrying Rbm42 compound heterozygous variants, c.280C>T (p.Q94*) and c.1306_1308delinsACA (p.A436T), demonstrated gross fetal developmental defects and most of the double mutant animals died by E13.5. RNA-seq data confirmed that Rbm42 was involved in neurological and myocardial functions with an essential role in alternative splicing (AS). Overall, we present clinical, genetic, and functional data to demonstrate that defects in RBM42 constitute the underlying etiology of a new neurodevelopmental disease which links the dysregulation of global AS to abnormal embryonic development.

Peripheral blood DNA methylation and neuroanatomical responses to HDACi treatment that rescues neurological deficits in a Kabuki syndrome mouse model

BACKGROUND

Recent findings from studies of mouse models of Mendelian disorders of epigenetic machinery strongly support the potential for postnatal therapies to improve neurobehavioral and cognitive deficits. As several of these therapies move into human clinical trials, the search for biomarkers of treatment efficacy is a priority. A potential postnatal treatment of Kabuki syndrome type 1 (KS1), caused by pathogenic variants in KMT2D encoding a histone-lysine methyltransferase, has emerged using a mouse model of KS1 (Kmt2d+/βGeo). In this mouse model, hippocampal memory deficits are ameliorated following treatment with the histone deacetylase inhibitor (HDACi), AR-42. Here, we investigate the effect of both Kmt2d+/βGeo genotype and AR-42 treatment on neuroanatomy and on DNA methylation (DNAm) in peripheral blood. While peripheral blood may not be considered a "primary tissue" with respect to understanding the pathophysiology of neurodevelopmental disorders, it has the potential to serve as an accessible biomarker of disease- and treatment-related changes in the brain.

METHODS

Half of the KS1 and wildtype mice were treated with 14 days of AR-42. Following treatment, fixed brain samples were imaged using MRI to calculate regional volumes. Blood was assayed for genome-wide DNAm at over 285,000 CpG sites using the Illumina Infinium Mouse Methylation array. DNAm patterns and brain volumes were analyzed in the four groups of animals: wildtype untreated, wildtype AR-42 treated, KS1 untreated and KS1 AR-42 treated.

RESULTS

We defined a DNAm signature in the blood of KS1 mice, that overlapped with the human KS1 DNAm signature. We also found a striking 10% decrease in total brain volume in untreated KS1 mice compared to untreated wildtype, which correlated with DNAm levels in a subset KS1 signature sites, suggesting that disease severity may be reflected in blood DNAm. Treatment with AR-42 ameliorated DNAm aberrations in KS1 mice at a small number of signature sites.

CONCLUSIONS

As this treatment impacts both neurological deficits and blood DNAm in mice, future KS clinical trials in humans could be used to assess blood DNAm as an early biomarker of therapeutic efficacy.

Germline pathogenic variants in HNRNPU are associated with alterations in blood methylome

HNRNPU encodes a multifunctional RNA-binding protein that plays critical roles in regulating pre-mRNA splicing, mRNA stability, and translation. Aberrant expression and dysregulation of HNRNPU have been implicated in various human diseases, including cancers and neurological disorders. We applied a next generation sequencing based assay (EPIC-NGS) to investigate genome-wide methylation profiling for >2 M CpGs for 7 individuals with a neurodevelopmental disorder associated with HNRNPU germline pathogenic loss-of-function variants. Compared to healthy individuals, 227 HNRNPU-associated differentially methylated positions were detected. Both hyper- and hypomethylation alterations were identified but the former predominated. The identification of a methylation episignature for HNRNPU-associated neurodevelopmental disorder (NDD) implicates HNPRNPU-related chromatin alterations in the aetiopathogenesis of this disorder and suggests that episignature profiling should have clinical utility as a predictor for the pathogenicity of HNRNPU variants of uncertain significance. The detection of a methylation episignaure for HNRNPU-associated NDD is consistent with a recent report of a methylation episignature for HNRNPK-associated NDD.

Integrative omics approaches to advance rare disease diagnostics

Over the past decade high-throughput DNA sequencing approaches, namely whole exome and whole genome sequencing became a standard procedure in Mendelian disease diagnostics. Implementation of these technologies greatly facilitated diagnostics and shifted the analysis paradigm from variant identification to prioritisation and evaluation. The diagnostic rates vary widely depending on the cohort size, heterogeneity and disease and range from around 30% to 50% leaving the majority of patients undiagnosed. Advances in omics technologies and computational analysis provide an opportunity to increase these unfavourable rates by providing evidence for disease-causing variant validation and prioritisation. This review aims to provide an overview of the current application of several omics technologies including RNA-sequencing, proteomics, metabolomics and DNA-methylation profiling for diagnostics of rare genetic diseases in general and inborn errors of metabolism in particular.

Episignature analysis of moderate effects and mosaics

DNA methylation classifiers ("episignatures") help to determine the pathogenicity of variants of uncertain significance (VUS). However, their sensitivity is limited due to their training on unambiguous cases with strong-effect variants so that the classification of variants with reduced effect size or in mosaic state may fail. Moreover, episignature evaluation of mosaics as a function of their degree of mosaicism has not been developed so far. We improved episignatures with respect to three categories. Applying (i) minimum-redundancy-maximum-relevance feature selection we reduced their length by up to one order of magnitude without loss of accuracy. Performing (ii) repeated re-training of a support vector machine classifier by step-wise inclusion of cases in the training set that reached probability scores larger than 0.5, we increased the sensitivity of the episignature-classifiers by 30%. In the newly diagnosed patients we confirmed the association between DNA methylation aberration and age at onset of KMT2B-deficient dystonia. Moreover, we found evidence for allelic series, including KMT2B-variants with moderate effects and comparatively mild phenotypes such as late-onset focal dystonia. Retrained classifiers also can detect mosaics that previously remained below the 0.5-threshold, as we showed for KMT2D-associated Kabuki syndrome. Conversely, episignature-classifiers are able to revoke erroneous exome calls of mosaicism, as we demonstrated by (iii) comparing presumed mosaic cases with a distribution of artificial in silico-mosaics that represented all the possible variation in degree of mosaicism, variant read sampling and methylation analysis.