DeNovoCNN: a deep learning approach to de novo variant calling in next generation sequencing data.

De novo mutations (DNMs) are an important cause of genetic disorders. The accurate identification of DNMs from sequencing data is therefore fundamental to rare disease research and diagnostics. Unfortunately, identifying reliable DNMs remains a major challenge due to sequence errors, uneven coverage, and mapping artifacts. Here, we developed a deep convolutional neural network (CNN) DNM caller (DeNovoCNN), that encodes the alignment of sequence reads for a trio as 160$ \times$164 resolution images. DeNovoCNN was trained on DNMs of 5616 whole exome sequencing (WES) trios achieving total 96.74% recall and 96.55% precision on the test dataset. We find that DeNovoCNN has increased recall/sensitivity and precision compared to existing DNM calling approaches (GATK, DeNovoGear, DeepTrio, Samtools) based on the Genome in a Bottle reference dataset and independent WES and WGS trios. Validations of DNMs based on Sanger and PacBio HiFi sequencing confirm that DeNovoCNN outperforms existing methods. Most importantly, our results suggest that DeNovoCNN is likely robust against different exome sequencing and analyses approaches, thereby allowing the application on other datasets. DeNovoCNN is freely available as a Docker container and can be run on existing alignment (BAM/CRAM) and variant calling (VCF) files from WES and WGS without a need for variant recalling.

Accepting or declining preconception expanded carrier screening: An exploratory study with 407 couples.

Rapidly evolving genomic technologies have made genetic expanded carrier screening (ECS) possible for couples considering a pregnancy. The aim of ECS is to identify couples at risk of having a child affected with a severe disorder and to facilitate their reproductive decision-making process. The ECS test we offer at our center, called BeGECS (Belgian Genetic ECS), consists of 1268 autosomal recessive (AR) and X-linked pathogenic genes, including severe childhood-onset disorders. However, thus far data are scarce regarding the actual uptake of preconception ECS in a clinical setting. Therefore, our aim was to describe the characteristics of 407 couples to whom ECS was offered at the Center for Medical Genetics of the University Hospital Ghent (CMGG). In addition, we aimed to identify their reasons for accepting or declining BeGECS. Between October 2019 and January 2023, 407 preconception couples were offered BeGECS and were asked to fill in a questionnaire after their decision. Of the 407 couples participating in the survey, 270 (66%) decided to take the test and 137 (34%) declined. We observed that age, highest education level as well as indication for consultation were statistically different between the group that accepted to take the test and the group that declined (p = 0.037). In particular, age and education level were substantially higher in the group that accepted the test. Major reasons for taking BeGECS include prevention, wishing to obtain all information possible, helping preparing their future reproductive decision and increasing their sense of control by being informed. However, couples that do not chose to take BeGECS stated that too much information would make them anxious, that the result would not change their decision to have children, that they do not want to spend money on something that will not happen and that they do not worry about their family history. These findings show that the majority of preconception couples that were offered ECS, accepted the test.

G protein-coupled receptor kinase 6 (GRK6) regulates insulin processing and secretion via effects on proinsulin conversion to insulin.

Recent studies identified a missense mutation in the gene coding for G protein-coupled receptor kinase 6 (GRK6) that segregates with type 2 diabetes (T2D). To better understand how GRK6 might be involved in T2D, we used pharmacological inhibition and genetic knockdown in the mouse ß-cell line, MIN6, to determine whether GRK6 regulates insulin dynamics. We show inhibition of GRK5 and GRK6 increased insulin secretion but reduced insulin processing while GRK6 knockdown revealed these same processing defects with reduced levels of cellular insulin. GRK6 knockdown cells also had attenuated insulin secretion but enhanced proinsulin secretion consistent with decreased processing. In support of these findings, we demonstrate GRK6 rescue experiments in knockdown cells restored insulin secretion after glucose treatment. The altered insulin profile appears to be caused by changes in the proprotein convertases, the enzymes responsible for proinsulin to insulin conversion, as GRK6 knockdown resulted in significantly reduced convertase expression and activity. To identify how the GRK6-P384S mutation found in T2D patients might affect insulin processing, we performed biochemical and cell biological assays to study the properties of the mutant. We found that while GRK6-P384S was more active than WT GRK6, it displayed a cytosolic distribution in cells compared to the normal plasma membrane localization of GRK6. Additionally, GRK6 overexpression in MIN6 cells enhanced proinsulin processing, while GRK6-P384S expression had little effect. Taken together, our data show that GRK6 regulates insulin processing and secretion in a glucose-dependent manner and provide a foundation for understanding the contribution of GRK6 to T2D.

IRF2BPL Is Associated with Neurological Phenotypes.

Interferon regulatory factor 2 binding protein-like (IRF2BPL) encodes a member of the IRF2BP family of transcriptional regulators. Currently the biological function of this gene is obscure, and the gene has not been associated with a Mendelian disease. Here we describe seven individuals who carry damaging heterozygous variants in IRF2BPL and are affected with neurological symptoms. Five individuals who carry IRF2BPL nonsense variants resulting in a premature stop codon display severe neurodevelopmental regression, hypotonia, progressive ataxia, seizures, and a lack of coordination. Two additional individuals, both with missense variants, display global developmental delay and seizures and a relatively milder phenotype than those with nonsense alleles. The IRF2BPL bioinformatics signature based on population genomics is consistent with a gene that is intolerant to variation. We show that the fruit-fly IRF2BPL ortholog, called pits (protein interacting with Ttk69 and Sin3A), is broadly detected, including in the nervous system. Complete loss of pits is lethal early in development, whereas partial knockdown with RNA interference in neurons leads to neurodegeneration, revealing a requirement for this gene in proper neuronal function and maintenance. The identified IRF2BPL nonsense variants behave as severe loss-of-function alleles in this model organism, and ectopic expression of the missense variants leads to a range of phenotypes. Taken together, our results show that IRF2BPL and pits are required in the nervous system in humans and flies, and their loss leads to a range of neurological phenotypes in both species.

Mutations in ATP6V1E1 or ATP6V1A Cause Autosomal-Recessive Cutis Laxa.

Defects of the V-type proton (H+) ATPase (V-ATPase) impair acidification and intracellular trafficking of membrane-enclosed compartments, including secretory granules, endosomes, and lysosomes. Whole-exome sequencing in five families affected by mild to severe cutis laxa, dysmorphic facial features, and cardiopulmonary involvement identified biallelic missense mutations in ATP6V1E1 and ATP6V1A, which encode the E1 and A subunits, respectively, of the V1 domain of the heteromultimeric V-ATPase complex. Structural modeling indicated that all substitutions affect critical residues and inter- or intrasubunit interactions. Furthermore, complexome profiling, a method combining blue-native gel electrophoresis and liquid chromatography tandem mass spectrometry, showed that they disturb either the assembly or the stability of the V-ATPase complex. Protein glycosylation was variably affected. Abnormal vesicular trafficking was evidenced by delayed retrograde transport after brefeldin A treatment and abnormal swelling and fragmentation of the Golgi apparatus. In addition to showing reduced and fragmented elastic fibers, the histopathological hallmark of cutis laxa, transmission electron microscopy of the dermis also showed pronounced changes in the structure and organization of the collagen fibers. Our findings expand the clinical and molecular spectrum of metabolic cutis laxa syndromes and further link defective extracellular matrix assembly to faulty protein processing and cellular trafficking caused by genetic defects in the V-ATPase complex.

A clinical scoring system for congenital contractural arachnodactyly.

PURPOSE: Congenital contractural arachnodactyly (CCA) is an autosomal dominant connective tissue disorder manifesting joint contractures, arachnodactyly, crumpled ears, and kyphoscoliosis as main features. Due to its rarity, rather aspecific clinical presentation, and overlap with other conditions including Marfan syndrome, the diagnosis is challenging, but important for prognosis and clinical management. CCA is caused by pathogenic variants in FBN2, encoding fibrillin-2, but locus heterogeneity has been suggested. We designed a clinical scoring system and diagnostic criteria to support the diagnostic process and guide molecular genetic testing. METHODS: In this retrospective study, we assessed 167 probands referred for FBN2 analysis and classified them into a FBN2-positive (n = 44) and FBN2-negative group (n = 123) following molecular analysis. We developed a 20-point weighted clinical scoring system based on the prevalence of ten main clinical characteristics of CCA in both groups. RESULTS: The total score was significantly different between the groups (P < 0.001) and was indicative for classifying patients into unlikely CCA (total score <7) and likely CCA (total score ≥7) groups. CONCLUSIONS: Our clinical score is helpful for clinical guidance for patients suspected to have CCA, and provides a quantitative tool for phenotyping in research settings.

Myhre syndrome: A first familial recurrence and broadening of the phenotypic spectrum.

Myhre syndrome is a rare multisystem connective tissue disorder, characterized by short stature, facial dysmorphology, variable intellectual disability, skeletal abnormalities, arthropathy, cardiopathy, laryngotracheal anomalies, and stiff skin. So far, all molecularly confirmed cases harbored a de novo heterozygous gain-of-function mutation in SMAD4, encoding the SMAD4 transducer protein required for both transforming growth factor-beta and bone morphogenic proteins signaling. We report on four novel patients (one female proband and her two affected children, and one male proband) with Myhre syndrome harboring the recurrent c.1486C>T (p.Arg496Cys) mutation in SMAD4. The female proband presented with a congenital heart defect, vertebral anomalies, and facial dysmorphic features. She developed severe tracheal stenosis requiring a total laryngectomy. With assisted reproductive treatment, she gave birth to two affected children. The second proband presented with visual impairment following lensectomy in childhood, short stature, brachydactyly, stiff skin, and decreased peripheral sensitivity. Transmission electron microscopy (TEM) of the dermis shows irregular elastin cores with globular deposits and almost absent surrounding microfibrils and suggests age-related increased collagen deposition. We report on the first familial case of Myhre syndrome and illustrate the variable clinical spectrum of the disorder. Despite the primarily fibrotic nature of the disease, TEM analysis mainly indicates elastic fiber anomalies.

Genetic Defects in TAPT1 Disrupt Ciliogenesis and Cause a Complex Lethal Osteochondrodysplasia.

The evolutionarily conserved transmembrane anterior posterior transformation 1 protein, encoded by TAPT1, is involved in murine axial skeletal patterning, but its cellular function remains unknown. Our study demonstrates that TAPT1 mutations underlie a complex congenital syndrome, showing clinical overlap between lethal skeletal dysplasias and ciliopathies. This syndrome is characterized by fetal lethality, severe hypomineralization of the entire skeleton and intra-uterine fractures, and multiple congenital developmental anomalies affecting the brain, lungs, and kidneys. We establish that wild-type TAPT1 localizes to the centrosome and/or ciliary basal body, whereas defective TAPT1 mislocalizes to the cytoplasm and disrupts Golgi morphology and trafficking and normal primary cilium formation. Knockdown of tapt1b in zebrafish induces severe craniofacial cartilage malformations and delayed ossification, which is shown to be associated with aberrant differentiation of cranial neural crest cells.

arrEYE: a customized platform for high-resolution copy number analysis of coding and noncoding regions of known and candidate retinal dystrophy genes and retinal noncoding RNAs.

PURPOSE: Our goal was to design a customized microarray, arrEYE, for high-resolution copy number variant (CNV) analysis of known and candidate genes for inherited retinal dystrophy (iRD) and retina-expressed noncoding RNAs (ncRNAs). METHODS: arrEYE contains probes for the full genomic region of 106 known iRD genes, including those implicated in retinitis pigmentosa (RP) (the most frequent iRD), cone-rod dystrophies, macular dystrophies, and an additional 60 candidate iRD genes and 196 ncRNAs. Eight CNVs in iRD genes identified by other techniques were used as positive controls. The test cohort consisted of 57 patients with autosomal dominant, X-linked, or simplex RP. RESULTS: In an RP patient, a novel heterozygous deletion of exons 7 and 8 of the HGSNAT gene was identified: c.634-408_820+338delinsAGAATATG, p.(Glu212Glyfs*2). A known variant was found on the second allele: c.1843G>A, p.(Ala615Thr). Furthermore, we expanded the allelic spectrum of USH2A and RCBTB1 with novel CNVs. CONCLUSION: The arrEYE platform revealed subtle single-exon to larger CNVs in iRD genes that could be characterized at the nucleotide level, facilitated by the high resolution of the platform. We report the first CNV in HGSNAT that, combined with another mutation, leads to RP, further supporting its recently identified role in nonsyndromic iRD.Genet Med 19 4, 457-466.

Tissue-specific mosaicism for a lethal osteogenesis imperfecta COL1A1 mutation causes mild OI/EDS overlap syndrome.

Type I collagen is the predominant protein of connective tissues such as skin and bone. Mutations in the type I collagen genes (COL1A1 and COL1A2) mainly cause osteogenesis imperfecta (OI). We describe a patient with clinical signs of Ehlers-Danlos syndrome (EDS), including fragile skin, easy bruising, recurrent luxations, and fractures resembling mild OI. Biochemical collagen analysis of the patients' dermal fibroblasts showed faint overmodification of the type I collagen bands, a finding specific for structural defects in type I collagen. Bidirectional Sanger sequencing detected an in-frame deletion in exon 44 of COL1A1 (c.3150_3158del), resulting in the deletion of three amino acids (p.Ala1053_Gly1055del) in the collagen triple helix. This COL1A1 mutation was hitherto identified in four probands with lethal OI, and never in EDS patients. As the peaks on the electropherogram corresponding to the mutant allele were decreased in intensity, we performed next generation sequencing of COL1A1 to study mosaicism in skin and blood. While approximately 9% of the reads originating from fibroblast gDNA harbored the COL1A1 deletion, the deletion was not detected in gDNA from blood. Most likely, the mild clinical symptoms observed in our patient can be explained by the mosaic state of the mutation.

Mitral regurgitation as a phenotypic manifestation of nonphotosensitive trichothiodystrophy due to a splice variant in MPLKIP.

BACKGROUND: Nonphotosensitive trichothiodystrophy (TTDN) is a rare autosomal recessive disorder of neuroectodermal origin. The condition is marked by hair abnormalities, intellectual impairment, nail dystrophies and susceptibility to infections but with no UV sensitivity. METHODS: We identified three consanguineous Pakistani families with varied TTDN features and used homozygosity mapping, linkage analysis, and Sanger and exome sequencing in order to identify pathogenic variants. Haplotype analysis was performed and haplotype age estimated. A splicing assay was used to validate the effect of the MPLKIP splice variant on expression. RESULTS: Affected individuals from all families exhibit several TTDN features along with a heart-specific feature, i.e. mitral regurgitation. Exome sequencing in the probands from families ED168 and ED241 identified a homozygous splice mutation c.339 + 1G > A within MPLKIP. The same splice variant co-segregates with TTDN in a third family ED210. The MPLKIP splice variant was not found in public databases, e.g. the Exome Aggregation Consortium, and in unrelated Pakistani controls. Functional analysis of the splice variant confirmed intron retention, which leads to protein truncation and loss of a phosphorylation site. Haplotype analysis identified a 585.1-kb haplotype which includes the MPLKIP variant, supporting the existence of a founder haplotype that is estimated to be 25,900 years old. CONCLUSION: This study extends the allelic and phenotypic spectra of MPLKIP-related TTDN, to include a splice variant that causes cardiomyopathy as part of the TTDN phenotype.

Flexible, scalable, and efficient targeted resequencing on a benchtop sequencer for variant detection in clinical practice.

The release of benchtop next-generation sequencing (NGS) instruments has paved the way to implement the technology in clinical setting. The need for flexible, qualitative, and cost-efficient workflows is high. We used singleplex-PCR for highly efficient target enrichment, allowing us to reach the quality standards set in Sanger sequencing-based diagnostics. For the library preparation, a modified NexteraXT protocol was used, followed by sequencing on a MiSeq instrument. With an innovative pooling strategy, high flexibility, scalability, and cost-efficiency were obtained, independent of the availability of commercial kits. The approach was validated for ∼250 genes associated with monogenic disorders. An overall sensitivity (>99%) similar to Sanger sequencing was observed in combination with a positive predictive value of >98%. The distribution of coverage was highly uniform, guaranteeing a minimal number of gaps to be filled with alternative methods. ISO15189-accreditation was obtained for the workflow. A major asset of the singleplex PCR-based enrichment is that new targets can be easily implemented. Diagnostic laboratories have validated assays available ensuring that the proposed workflow can easily be adopted. Although our platform was optimized for constitutional variant detection of monogenic disease genes, it is now also used as a model for somatic mutation detection in acquired diseases.

Novel pathogenic COL11A1/COL11A2 variants in Stickler syndrome detected by targeted NGS and exome sequencing.

INTRODUCTION: Stickler syndrome is caused by mutations in genes encoding type II and type XI collagens. About 85% of the pathogenic variants is found in COL2A1 (Stickler type 1), whereas a minority of mutations has been reported in COL11A1 (Stickler type 2) and COL11A2 (Stickler type 3). Beside the typical skeletal and orofacial manifestations, ocular anomalies are predominantly present in type 1 and type 2, while hearing loss is more pronounced in type 2 and type 3. METHODS: We performed COL11A1 mutation analysis for 40 type 2 Stickler patients and COL11A2 mutation analysis for five type 3 Stickler patients, previously all COL2A1 mutation-negative, using targeted next-generation sequencing (NGS) whereas whole-exome sequencing (WES) was performed in parallel for two patients. Three patients were analyzed for both genes due to unclear ocular findings. RESULTS: In total 14 COL11A1 and two COL11A2 mutations could be identified, seven of which are novel. Splice site alterations are the most frequent mutation type, followed by glycine substitutions. In addition, six variants of unknown significance (VUS) have been found. Identical mutations and variants were identified with both NGS techniques. CONCLUSION: We expand the mutation spectrum of COL11A1 and COL11A2 in Stickler syndrome patients and show that targeted NGS is an efficient and cost-effective molecular tool in the genetic diagnosis of Stickler syndrome, whereas the more standardized WES might be an alternative approach.

Mobile element insertions in rare diseases: a comparative benchmark and reanalysis of 60,000 exome samples.

Mobile element insertions (MEIs) are a known cause of genetic disease but have been underexplored due to technical limitations of genetic testing methods. Various bioinformatic tools have been developed to identify MEIs in Next Generation Sequencing data. However, most tools have been developed specifically for genome sequencing (GS) data rather than exome sequencing (ES) data, which remains more widely used for routine diagnostic testing. In this study, we benchmarked six MEI detection tools (ERVcaller, MELT, Mobster, SCRAMble, TEMP2 and xTea) on ES data and on GS data from publicly available genomic samples (HG002, NA12878). For all the tools we evaluated sensitivity and precision of different filtering strategies. Results show that there were substantial differences in tool performance between ES and GS data. MELT performed best with ES data and its combination with SCRAMble increased substantially the detection rate of MEIs. By applying both tools to 10,890 ES samples from Solve-RD and 52,624 samples from Radboudumc we were able to diagnose 10 patients who had remained undiagnosed by conventional ES analysis until now. Our study shows that MELT and SCRAMble can be used reliably to identify clinically relevant MEIs in ES data. This may lead to an additional diagnosis for 1 in 3000 to 4000 patients in routine clinical ES.

Unravelling undiagnosed rare disease cases by HiFi long-read genome sequencing.

Solve-RD is a pan-European rare disease (RD) research program that aims to identify disease-causing genetic variants in previously undiagnosed RD families. We utilised 10-fold coverage HiFi long-read sequencing (LRS) for detecting causative structural variants (SVs), single nucleotide variants (SNVs), insertion-deletions (InDels), and short tandem repeat (STR) expansions in extensively studied RD families without clear molecular diagnoses. Our cohort includes 293 individuals from 114 genetically undiagnosed RD families selected by European Rare Disease Network (ERN) experts. Of these, 21 families were affected by so-called 'unsolvable' syndromes for which genetic causes remain unknown, and 93 families with at least one individual affected by a rare neurological, neuromuscular, or epilepsy disorder without genetic diagnosis despite extensive prior testing. Clinical interpretation and orthogonal validation of variants in known disease genes yielded thirteen novel genetic diagnoses due to de novo and rare inherited SNVs, InDels, SVs, and STR expansions. In an additional four families, we identified a candidate disease-causing SV affecting several genes including an MCF2 / FGF13 fusion and PSMA3 deletion. However, no common genetic cause was identified in any of the 'unsolvable' syndromes. Taken together, we found (likely) disease-causing genetic variants in 13.0% of previously unsolved families and additional candidate disease-causing SVs in another 4.3% of these families. In conclusion, our results demonstrate the added value of HiFi long-read genome sequencing in undiagnosed rare diseases.

Systematic analysis of paralogous regions in 41,755 exomes uncovers clinically relevant variation.

The short lengths of short-read sequencing reads challenge the analysis of paralogous genomic regions in exome and genome sequencing data. Most genetic variants within these homologous regions therefore remain unidentified in standard analyses. Here, we present a method (Chameleolyser) that accurately identifies single nucleotide variants and small insertions/deletions (SNVs/Indels), copy number variants and ectopic gene conversion events in duplicated genomic regions using whole-exome sequencing data. Application to a cohort of 41,755 exome samples yields 20,432 rare homozygous deletions and 2,529,791 rare SNVs/Indels, of which we show that 338,084 are due to gene conversion events. None of the SNVs/Indels are detectable using regular analysis techniques. Validation by high-fidelity long-read sequencing in 20 samples confirms >88% of called variants. Focusing on variation in known disease genes leads to a direct molecular diagnosis in 25 previously undiagnosed patients. Our method can readily be applied to existing exome data.

Hypergastrinemia, a clue leading to the identification of an atypical form of diabetes mellitus type 2.

BACKGROUND: A hitherto undescribed form of diabetes mellitus type 2 is reported in a Flemish family. In these patients, markedly elevated gastrin levels were observed, which could not be linked to gastrointestinal symptoms. MATERIALS AND METHODS: Gel permeation chromatography was performed for gastrin, insulin, and proinsulin. Proprotein convertase subtilisin/kexin type (PCSK1 and PCSK2)] were sequenced. Whole-exome sequencing was performed on the genomic DNA extracted from leukocytes of the proband of the family. RESULTS: Gel permeation chromatography revealed that the apparent hypergastrinemia was caused by the accumulation of biologically inactive progastrin. Besides, high serum concentrations of proinsulin and intact fibroblast growth factor 23 (FGF23) were also detected. Sequencing of PCSK1 and PCSK2 genes did not reveal any mutations in these genes. Whole exome sequencing revealed a c.1150C > T (p.Pro384Ser) mutation in G protein-coupled receptor kinase 6 (GRK6), which cosegregated with the disease. Expression of the mutant enzyme in mammalian cells revealed that it was mislocalized compared to the wild-type GRK6. CONCLUSIONS: In the affected patients, prohormone processing is impaired likely due to the altered function of mutant GRK6. Delayed pro-insulin processing causes hypoglycaemia episodes a couple of hours following meals. In addition, increased plasma concentrations of progastrin and intact FGF23 in the affected individuals can be explained by incomplete processing of the precursor hormones.

Shortcutting the diagnostic odyssey: the multidisciplinary Program for Undiagnosed Rare Diseases in adults (UD-PrOZA).

BACKGROUND: In order to facilitate the diagnostic process for adult patients suffering from a rare disease, the Undiagnosed Disease Program (UD-PrOZA) was founded in 2015 at the Ghent University Hospital in Belgium. In this study we report the five-year results of our multidisciplinary approach in rare disease diagnostics. METHODS: Patients referred by a healthcare provider, in which an underlying rare disease is likely, qualify for a UD-PrOZA evaluation. UD-PrOZA uses a multidisciplinary clinical approach combined with state-of-the-art genomic technologies in close collaboration with research facilities to diagnose patients. RESULTS: Between 2015 and 2020, 692 patients (94% adults) were referred of which 329 (48%) were accepted for evaluation. In 18% (60 of 329) of the cases a definite diagnosis was made. 88% (53 of 60) of the established diagnoses had a genetic origin. 65% (39 of 60) of the genetic diagnoses were made through whole exome sequencing (WES). The mean time interval between symptom-onset and diagnosis was 19 years. Key observations included novel genotype-phenotype correlations, new variants in known disease genes and the identification of three new disease genes. In 13% (7 of 53), identifying the molecular cause was associated with therapeutic recommendations and in 88% (53 of 60), gene specific genetic counseling was made possible. Actionable secondary findings were reported in 7% (12 of 177) of the patients in which WES was performed. CONCLUSION: UD-PrOZA offers an innovative interdisciplinary platform to diagnose rare diseases in adults with previously unexplained medical problems and to facilitate translational research.