Clinical Variant Interpretation Research Articles

Predicting functional UTR variants by integrating region-specific features.

The untranslated region (UTR) of messenger ribonucleic acid (mRNA), including the 5'UTR and 3'UTR, plays a critical role in regulating gene expression and translation. Variants within the UTR can lead to changes associated with human traits and diseases; however, computational prediction of UTR variant effect is challenging. Current noncoding variant prediction mainly focuses on the promoters and enhancers, neglecting the unique sequence of the UTR and thereby limiting their predictive accuracy. In this study, using consolidated datasets of UTR variants from disease databases and large-scale experimental data, we systematically analyzed more than 50 region-specific features of UTR, including functional elements, secondary structure, sequence composition and site conservation. Our analysis reveals that certain features, such as C/G-related sequence composition in 5'UTR and A/T-related sequence composition in 3'UTR, effectively differentiate between nonfunctional and functional variant sets, unveiling potential sequence determinants of functional UTR variants. Leveraging these insights, we developed two classification models to predict functional UTR variants using machine learning, achieving an area under the curve (AUC) value of 0.94 for 5'UTR and 0.85 for 3'UTR, outperforming all existing methods. Our models will be valuable for enhancing clinical interpretation of genetic variants, facilitating the prediction and management of disease risk.

Clinical Interpretation of Genetic Variants in the Evaluation and Management of Thoracic Aortic Aneurysm and Dissection

We aimed to elucidate clinical implications of genetic variant interpretation in assessing disease severity and progression in thoracic aortic aneurysm and dissection (TAAD) patients. Consecutive TAAD patients with aortic root and/or ascending aortic aneurysms seen between 2011 and 2020 were included. Serial echocardiography, family history of TAAD, and management information were retrospectively collected and analyzed. Patients were classified into gene-positive (Gen-P), variants of uncertain significance, and gene-negative (Gen-N) groups. A total of 407 patients were included: mean age 53.7±15.4 years, 64.4% women, and 38% with reported family history of TAAD. Thirty-seven (9.1%) were Gen-P; 147 (36.1%) had a variant of uncertain significance. Maximal aneurysm diameter was 4.78 mm larger in Gen-P than the other groups (P=.0003). In 162 unoperated TAAD patients with serial echocardiographic measurements, aneurysms enlarged at a significantly higher rate in the Gen-P (1.36 mm/year, 95% CI: 0.77-1.95) than variants of uncertain significance and Gen-N groups (0.83 mm/year vs 0.89 mm/year, respectively; P<.001). Aneurysms were 20% more likely to require surgical intervention for every millimeter increase in diameter. When considered on an individual basis, the highest growth rates were found in the variants of uncertain significance group. While aneurysms linked to variants of uncertain significance demonstrate average growth rates comparable to those in Gen-N, close follow-up and genetic counseling in the variants of uncertain significance group are recommended for assessment of pathogenicity on a case-by-case basis. Early familial gene testing in TAAD is important to develop individualized preventive and therapeutic criteria.

Pacybara: accurate long-read sequencing for barcoded mutagenized allelic libraries.

Long-read sequencing technologies, an attractive solution for many applications, often suffer from higher error rates. Alignment of multiple reads can improve base-calling accuracy, but some applications, e.g. sequencing mutagenized libraries where multiple distinct clones differ by one or few variants, require the use of barcodes or unique molecular identifiers. Unfortunately, sequencing errors can interfere with correct barcode identification, and a given barcode sequence may be linked to multiple independent clones within a given library. Here we focus on the target application of sequencing mutagenized libraries in the context of multiplexed assays of variant effects (MAVEs). MAVEs are increasingly used to create comprehensive genotype-phenotype maps that can aid clinical variant interpretation. Many MAVE methods use long-read sequencing of barcoded mutant libraries for accurate association of barcode with genotype. Existing long-read sequencing pipelines do not account for inaccurate sequencing or nonunique barcodes. Here, we describe Pacybara, which handles these issues by clustering long reads based on the similarities of (error-prone) barcodes while also detecting barcodes that have been associated with multiple genotypes. Pacybara also detects recombinant (chimeric) clones and reduces false positive indel calls. In three example applications, we show that Pacybara identifies and correctly resolves these issues. Pacybara, freely available at https://github.com/rothlab/pacybara, is implemented using R, Python, and bash for Linux. It runs on GNU/Linux HPC clusters via Slurm, PBS, or GridEngine schedulers. A single-machine simplex version is also available.

Clinical and genetic interpretation of uncertain DMD missense variants: evidence from mRNA and protein studies

BackgroundPathogenic missense variants in the dystrophin (DMD) gene are rarely reported in dystrophinopathies. Most DMD missense variants are of uncertain significance and their pathogenicity interpretation remains complicated. We aimed to investigate whether DMD missense variants would cause aberrant splicing and re-interpret their pathogenicity based on mRNA and protein studies.MethodsNine unrelated patients who had an elevated serum creatine kinase level with or without muscle weakness were enrolled. They underwent a detailed clinical, imaging, and pathological assessment. Routine genetic testing and muscle-derived mRNA and protein studies of dystrophin and sarcoglycan genes were performed in them.ResultsThree of the 9 patients presented with a Duchenne muscular dystrophy (DMD) phenotype and the remaining 6 patients had a suspected diagnosis of Becker muscular dystrophy (BMD) or sarcoglycanopathy based on their clinical and pathological characteristics. Routine genetic testing detected only 9 predicted DMD missense variants in them, of which 6 were novel and interpreted as uncertain significance. Muscle-derived mRNA studies of sarcoglycan genes didn’t reveal any aberrant transcripts in them. Dystrophin mRNA studies confirmed that 3 predicted DMD missense variants (c.2380G > C, c.4977C > G, and c.5444A > G) were in fact splicing and frameshift variants due to aberrant splicing. The 9 DMD variants were re-interpreted as pathogenic or likely pathogenic based on mRNA and protein studies. Therefore, 3 patients with DMD splicing variants and 6 patients with confirmed DMD missense variants were diagnosed with DMD and BMD, respectively.ConclusionOur study highlights the importance of muscle biopsy and aberrant splicing for clinical and genetic interpretation of uncertain DMD missense variants.

KCNQ1 p.D446E Variant as a Risk Allele for Arrhythmogenic Phenotypes: Electrophysiological Characterization Reveals a Complex Phenotype Affecting the Slow Delayed Rectifier Potassium Current (IKs) Voltage Dependence by Causing a Hyperpolarizing Shift and a Lack of Response to Protein Kinase A Activation.

Genetic testing is crucial in inherited arrhythmogenic channelopathies; however, the clinical interpretation of genetic variants remains challenging. Incomplete penetrance, oligogenic, polygenic or multifactorial forms of channelopathies further complicate variant interpretation. We identified the KCNQ1/p.D446E variant in 2/63 patients with long QT syndrome, 30-fold more frequent than in public databases. We thus characterized the biophysical phenotypes of wildtype and mutant IKs co-expressing these alleles with the β-subunit minK in HEK293 cells. KCNQ1 p.446E homozygosity significantly shifted IKs voltage dependence to hyperpolarizing potentials in basal conditions (gain of function) but failed to shift voltage dependence to hyperpolarizing potentials (loss of function) in the presence of 8Br-cAMP, a protein kinase A activator. Basal IKs activation kinetics did not differ among genotypes, but in response to 8Br-cAMP, IKs 446 E/E (homozygous) activation kinetics were slower at the most positive potentials. Protein modeling predicted a slower transition of the 446E Kv7.1 tetrameric channel to the stabilized open state. In conclusion, biophysical and modelling evidence shows that the KCNQ1 p.D446E variant has complex functional consequences including both gain and loss of function, suggesting a contribution to the pathogenesis of arrhythmogenic phenotypes as a functional risk allele.

Multisite clinical cross-validation and variant interpretation of a next generation sequencing panel for lymphoid cancer prognostication

AimsGenomic sequencing of lymphomas is under-represented in routine clinical testing despite having prognostic and predictive value. Clinical implementation is challenging due to a lack of consensus on reportable targets and...

A Study on the Retrospective Reinterpretation of BRCA1 and BRCA2 Variants.

Hereditary breast/ovarian cancer is associated with BRCA gene mutations. As large volumes of clinical data on BRCA variants are continuously updated, their clinical interpretation may change, leading to their reclassification. This study analyzed the class and proportion of the changed clinical interpretations of BRCA variants to validate the need for periodic reviews of these variants. This retrospective study reinterpreted previously reported BRCA1 and BRCA2 exon variants according to the 2015 American College of Medical Genetics and Genomics guidelines and the clinical significance of the recent public genomic database. Reanalyzed results were obtained for patients tested for BRCA genetic mutation for 10 years and 4 months. We included data from 4,058 patients, with 595 having at least one pathogenic variant (P), likely pathogenic variant (LP), or variant of uncertain significance (VUS) at a detection rate of 14.66%. The numbers of exon and intron variants were 562 (87.81%) and 78 (12.19%), respectively. BRCA1 exhibited a significantly higher P/LP detection rate of 6.96% compared to that of BRCA2 at 6.89% (p < 0.001). Conversely, BRCA2 demonstrated a significantly higher VUS rate of 10.38% compared to that of BRCA1 at 5.08% (p < 0.001). Among BRCA1 mutations, substitutions were the most prevalent in P/LP and VUS. Among BRCA2 mutations, deletions were most prevalent in P/LP, and substitutions were most prevalent in VUS. Among the 131 patients with P/LP in BRCA1 exons, the clinical interpretation was reclassified in two cases (1.53%), one VUS and one benign/likely benign (B/LB), and 48 cases (48.00%) with VUS were reclassified; one to P/LP and 47 to B/LB. Among the 138 patients with P/LP in BRCA2 exons, the clinical interpretation was reclassified in six (4.35%), five to VUS, and one to B/LB, and all 74 with VUS were reclassified to B/LB. We determined the class and proportion of reclassified BRCA variants. In conclusion, reviews are required to provide clinical guidance, such as determining treatment direction and preventive measures in the future.

Whole Exome Sequencing of Patients with Adult-Onset Evans Syndrome: A Cohort of 80 Patients

Introduction Loss of tolerance toward several self-antigens suggests an underlying genetic predisposition. A previous study (1) conducted in children with Evans syndrome revealed a high prevalence of pathogenic mutations in genes involved in primary immunodeficiencies. Whether these findings are restricted to children is unknown. In this study, we assessed the prevalence of constitutional genetic variants in a cohort of patients with adult onset Evans syndrome. Patients and methods We consecutively included from November 2021 to June 2023 patients that had been diagnosed with adult onset (≥18 years) Evans syndrome (association of immune thrombocytopenia (ITP), warm autoimmune hemolytic anemia (wAIHA) and/or autoimmune neutropenia (AIN) according to international guidelines (2,3)), and identified in France throughout the network of the national reference center for adult' autoimmune cytopenia. We excluded patients with a systemic lupus (according to Systemic Lupus International Collaborating Clinics criteria (4)), and patients with indolent B cell malignancies at Evans syndrome onset. Clinical and biological data were retrospectively collected using a standardized form. Patients underwent whole-exome sequencing after written and informed consent was obtained. Gene variants already published and/or with in vitro confirmed consequences were considered as genetic diagnoses. Clinical interpretation of variants was performed according to the ACMG guidelines (5). A patient was classified as having a genetic diagnosis if carryinghemizygous/heterozygous pathogenic or likely pathogenic variant (for X-linked or autosomal dominant conditions), or 2 pathogenic or likely pathogenic variants in the same gene (for autosomal recessive conditions). Results We identified 80 patients (40% female, median age 31 years at Evans syndrome diagnosis [range 18-76]) with adult-onset Evans syndrome from 19 centers. Median age at first cytopenia was 28 years [range 1-73], and 13 patients (16%) were under 18 years at first cytopenia. 78 patients (96%) had ITP (chronic in 87%), 59 (73%) had wAIHA (with at least one relapse in 58%), and 38 (47%) had AIN (chronic in 74%). Median delay between first and second cytopenia was 18 months (range 0 - 329) and 28 patients (35%) had synchronous onset of cytopenia. Twenty-four patients (30%) had associated immune manifestation (involving endocrine system in 9%, lung in 9%, gastrointestinal tract in 6%, skin in 5%, central nervous system in 4%) and 28% had antinuclear antibody titers ≥ 1/160. Lymphoproliferation was found in 56%, including lymphadenopathy in 41% and splenomegaly in 35%. Nine patients (11%) had lymphoma or cancer history. Twenty patients (25%) had humoral immune defect, including 13 (16%) with a common variable immunodeficiency (CVID)-like phenotype. In the whole cohort, 9 patients (11.25%) had a genetic diagnosis that could be linked to Evans syndrome, with heterozygous variants in CTLA4, STAT3, NFKB1, CYBB, TNFAIP3, DDX41, MYH9 and homozygous variant in PIK3CG. Twenty (25%) patients had genetic testing prior to this study (targeted Sanger sequencing [N=3], or NGS panel [N=17]), resulting in 2 genetic diagnoses ( CYBB and TNFAIP3). A family history of immune manifestations in first-degree relatives was found in 56% of the patients with genetic diagnosis versus 20% of patients without (P=0.0308). However, the proportion of patients with CVID-like phenotype, associated immune disorder, lymphoproliferation, cancer/lymphoma, positive antinuclear antibodies, or pediatric onset of first cytopenia was not significantly increased in patients with genetic diagnosis. Discussion As expected, the proportion of genetic diagnoses in patients with adult onset Evans syndrome was lower that what was previously described in children, but led to a significant impact on clinical management in some patients. We did not find clinical or biological features associated with a genetic diagnosis, suggesting that genetic testing should be considered in every adult patient diagnosed with Evans syndrome in the absence of any obvious underlying cause or condition. References (1) Hadjadj J et al., Blood 2019; 134: 9-21. (2) Provan D et al., Blood Adv 2019; 3: 3780-817. (3) Jäger U et al., Blood Rev 2020; 41: 100648. (4) Petri M et al., Arthritis Rheum 2012; 64: 2677-86. (5) Richards S et al., Genet Med 2015; 17: 405-24.

Massive open online courses (MOOCs) in genomic variant interpretation: An innovative education strategy for the growing genetic counselor workforce.

The growth in genomic testing in healthcare requires a highly trained specialist workforce to ensure evidence based clinical germline variant interpretation. Genetic counselors form a core part of the clinical genomics multidisciplinary team (MDT) and represent a growing workforce participating in variant interpretation from data analysis to the patient consultation. Standardized, high-quality variant interpretation training for Genetic Counselors has historically been ad hoc and variable, with existing programs lacking capacity to reach the entire workforce. To address the requirement for scalable variant interpretation training for genomics healthcare professionals (HCPs), two Massive Open Online Courses (MOOCs) were developed. We analyzed the data from 17 Genetic counselors, as part of an evaluation cohort completing the first run of these MOOCs. Overall genetic counselors enjoyed the courses, felt they were clinically relevant and would recommend them to colleagues. Common challenges amongst the genetic counseling workforces included utilizing relevant databases and finding time in the workday to complete training. These findings suggest MOOCs could be an acceptable option to ensure a consistent and transferrable high standard of training, complimentary to existing curricula. They also hold the potential to facilitate large-scale education to update the genetic counseling workforce when changes in variant interpretation guidance occur.

Clinical phenotype and genetic analysis of patients with left ventricular noncompaction caused by the biallelic mutation of MYBPC3 and MYH7

Objective: To explore the relationship between pathogenic gene, mutation and phenotype of left ventricular noncompaction (LVNC) patients and their family members. Methods: The subjects were the proband with LVNC and her family members. The medical history including electrocardiogram, echocardiography and cardiac magnetic resonance examination of the proband and family members were collected. Whole exome sequencing of the proband was performed, bioinformatics analysis focused on the genes related to hereditary cardiomyopathy. Candidate pathogenic sites were validated by Sanger sequencing. The clinical interpretation of sequence variants were classified according to American College of Medical Genetics and Genomics (ACMG) guidelines. Results: The proband carried a heterozygous variation of the MYBPC3 gene c.C2827T and the MYH7 gene c.G2221C. The proband's sister carried heterozygous variation of MYBPC3 gene c.C2827T. According to the ACMG guidelines, the variant was determined to be pathogenic. Conclusion: The missense variant of MYBPC3 gene c.C2827T and MYH7 gene c.G2221C are identified from the proband with LVNC and her family member, which provides a genetic basis for clinical diagnosis and genetic counseling of the patients and the family members with LVNC.

Should secondary pharmacogenomic variants be actively screened and reported when diagnostic genome-wide sequencing is performed in a child?

This white paper was prepared by the Global Alliance for Genomics and Health Regulatory and Ethics Work Stream’s Pediatric Task Team to review and provide perspective with respect to ethical, legal, and social issues regarding the return of secondary pharmacogenomic variants in children who have a serious disease or developmental disorder and are undergoing exome or genome sequencing to identify a genetic cause of their condition. We discuss actively searching for and reporting pharmacogenetic/genomic variants in pediatric patients, different methods of returning secondary pharmacogenomic findings to the patient/parents and/or treating clinicians, maintaining these data in the patient's health record over time, decision supports to assist using pharmacogenetic results in future treatment decisions, and sharing information in public databases to improve the clinical interpretation of pharmacogenetic variants identified in other children. We conclude by presenting a series of points to consider for clinicians and policymakers regarding whether, and under what circumstances, routine screening and return of pharmacogenomic variants unrelated to the indications for testing is appropriate in children who are undergoing genome-wide sequencing to assist in the diagnosis of a suspected genetic disease.

Clinical relevance of genetic variants in the von Willebrand factor according to in-silico methods.

Clinical interpretation of genetic variants in the context of the patient's phenotype is a time-consuming and costly process. In-silico analysis using in-silico prediction tools, and molecular modeling have been developed to predict the influence of genetic variants on the quality and/or quantity of the resulting translated protein, and in this way, to alert clinicians of disease likelihood in the absence of previous evidence. Our objectives were to evaluate the success rate of the in-silico analysis in predicting the disease-causing variants as pathogenic and the single-nucleotide variants as neutral, and to establish the reliability of in-silico analysis for determining pathogenicity or neutrality of von Willebrand factor gene-associated genetic variants. Using in-silico analysis, we studied pathogenicity in 31 disease-causing variants, and neutrality in 61 single-nucleotide variants from patients previously diagnosed as type 2 von Willebrand disease. Disease-causing variants and non-synonymous single-nucleotide variants were explored by in-silico tools that analyze the amino acidic sequence. Intronic and synonymous single-nucleotide variants were analyzed by in-silico methods that evaluate the nucleotidic sequence. We found a consistent agreement between predictions achieved by in-silico prediction tools and molecular modeling, both for defining the pathogenicity of disease-causing variants and the neutrality of single-nucleotide variants. Based on our results, the in-silico analysis would help to define the pathogenicity or neutrality in novel genetic variants observed in patients with clinical and laboratory phenotypes suggestive of von Willebrand disease.

Constructing and interpreting a large-scale variant effect map for an ultrarare disease gene: Comprehensive prediction of the functional impact of PSAT1 genotypes.

Reduced activity of the enzymes encoded by PHGDH, PSAT1, and PSPH causes a set of ultrarare, autosomal recessive diseases known as serine biosynthesis defects. These diseases present in a broad phenotypic spectrum: at the severe end is Neu-Laxova syndrome, in the intermediate range are infantile serine biosynthesis defects with severe neurological manifestations and growth deficiency, and at the mild end is childhood disease with intellectual disability. However, L-serine supplementation, especially if started early, can ameliorate and in some cases even prevent symptoms. Therefore, knowledge of pathogenic variants can improve clinical outcomes. Here, we use a yeast-based assay to individually measure the functional impact of 1,914 SNV-accessible amino acid substitutions in PSAT. Results of our assay agree well with clinical interpretations and protein structure-function relationships, supporting the inclusion of our data as functional evidence as part of the ACMG variant interpretation guidelines. We use existing ClinVar variants, disease alleles reported in the literature and variants present as homozygotes in the primAD database to define assay ranges that could aid clinical variant interpretation for up to 98% of the tested variants. In addition to measuring the functional impact of individual variants in yeast haploid cells, we also assay pairwise combinations of PSAT1 alleles that recapitulate human genotypes, including compound heterozygotes, in yeast diploids. Results from our diploid assay successfully distinguish the genotypes of affected individuals from those of healthy carriers and agree well with disease severity. Finally, we present a linear model that uses individual allele measurements to predict the biallelic function of ~1.8 million allele combinations corresponding to potential human genotypes. Taken together, our work provides an example of how large-scale functional assays in model systems can be powerfully applied to the study of ultrarare diseases.

How human genetic context can inform pathogenicity classification: FGFR1 variation in idiopathic hypogonadotropic hypogonadism.

Precision medicine requires precise genetic variant interpretation, yet many disease-associated genes have unresolved variants of unknown significance (VUS). We analyzed variants in a well-studied gene, FGFR1, a common cause of Idiopathic Hypogonadotropic Hypogonadism (IHH) and examined whether regional genetic enrichment of missense variants could improve variant classification. FGFR1 rare sequence variants (RSVs) were examined in a large cohort to (i) define regional genetic enrichment, (ii) determine pathogenicity based on the American College of Medical Genetics/Association for Molecular Pathology (ACMG/AMP) variant classification framework, and (iii) characterize the phenotype of FGFR1 variant carriers by variant classification. A total of 143 FGFR1 RSVs were identified in 175 IHH probands (n = 95 missense, n = 48 protein-truncating variants). FGFR1 missense RSVs showed regional enrichment across biologically well-defined domains: D1, D2, D3, and TK domains and linker regions (D2-D3, TM-TK). Using these defined regions of enrichment to augment the ACMG/AMP classification reclassifies 37% (20/54) of FGFR1 missense VUS as pathogenic or likely pathogenic (PLP). Non-proband carriers of FGFR1 missense VUS variants that were reclassified as PLP were more likely to express IHH or IHH-associated phenotypes [anosmia or delayed puberty] than non-proband carriers of FGFR1 missense variants that remained as VUS (76.9% vs 34.7%, p = 0.035). Using the largest cohort of FGFR1 variant carriers, we show that integration of regional genetic enrichment as moderate evidence for pathogenicity improves the classification of VUS and that reclassified variants correlated with phenotypic expressivity. The addition of regional genetic enrichment to the ACMG/AMP guidelines may improve clinical variant interpretation.

Nucleotide substitutions at the p.Gly117 and p.Thr180 mutational hot-spots of SKI alter molecular dynamics and may affect cell cycle.

Heterozygous deleterious variants in SKI cause Shprintzen-Goldberg Syndrome, which is mainly characterized by craniofacial features, neurodevelopmental disorder and thoracic aorta dilatations/aneurysms. The encoded protein is a member of the transforming growth factor beta signaling. Paucity of reported studies exploring the SGS molecular pathogenesis hampers disease recognition and clinical interpretation of private variants. Here, the unpublished c.349G>A, p.[Gly117Ser] and the recurrent c.539C>T, p.[Thr180Met] SKI variants were studied combining in silico and in vitro approach. 3D comparative modeling and calculation of the interaction energy predicted that both variants alter the SKI tertiary protein structure and its interactions. Computational data were functionally corroborated by the demonstration of an increase of MAPK phosphorylation levels and alteration of cell cycle in cells expressing the mutant SKI. Our findings confirmed the effects of SKI variants on MAPK and opened the path to study the role of perturbations of the cell cycle in SGS.

Functional evaluation allows ACMG/AMP-based re-classification of CNGA3 variants associated with achromatopsia

PurposeCNGA3 encoding the main subunit of the cyclic nucleotide-gated ion channel in cone photoreceptors is one of the major disease-associated genes for achromatopsia. Most CNGA3 variants are missense variants with the majority being functionally uncharacterized and therefore hampering genetic diagnosis. In light of potential gene therapy, objective variant pathogenicity assessment is essential. MethodsWe established a medium-throughput aequorin-based luminescence bioassay allowing mutant CNGA3 channel function assessment via quantification of CNGA3 channel-mediated calcium influx in a cell culture system, thereby enabling American College of Medical Genetics and Genomics/Association for Molecular Pathology–based variant re-classification. ResultsWe provide functional read-out obtained for 150 yet uncharacterized CNGA3 missense substitutions of which 55 were previously categorized as variants of uncertain significance (VUS) identifying 25 as functionally normal and 125 as functionally abnormal. These data enabled the American College of Medical Genetics and Genomics/ Association for Molecular Pathology–based variant re-classification of 52/55 VUS as either benign, likely benign, or likely pathogenic reaching a VUS re-classification rate of 94.5%. ConclusionOur aequorin-based bioassay allows functionally ensured clinical variant interpretation for 150 CNGA3 missense variants enabling and supporting VUS re-classification and assuring molecular diagnosis to patients affected by CNGA3-associated achromatopsia, hereby identifying patients eligible for future gene therapy trials on this disease.

The mutational profile in a South African cohort with inherited neuropathies and spastic paraplegia.

Limited diagnostics are available for inherited neuromuscular diseases (NMD) in South Africa and (excluding muscle disease) are mainly aimed at the most frequent genes underlying genetic neuropathy (GN) and spastic ataxias in Europeans. In this study, we used next-generation sequencing to screen 61 probands with GN, hereditary spastic paraplegia (HSP), and spastic ataxias for a genetic diagnosis. After identifying four GN probands with PMP22 duplication and one spastic ataxia proband with SCA1, the remaining probands underwent whole exome (n = 26) or genome sequencing (n = 30). The curation of coding/splice region variants using gene panels was guided by allele frequencies from internal African-ancestry control genomes (n = 537) and the Clinical Genome Resource's Sequence Variant Interpretation guidelines. Of 32 GN probands, 50% had African-genetic ancestry, and 44% were solved: PMP22 (n = 4); MFN2 (n = 3); one each of MORC2, ATP1A1, ADPRHL2, GJB1, GAN, MPZ, and ATM. Of 29 HSP probands (six with predominant ataxia), 66% had African-genetic ancestry, and 48% were solved: SPG11 (n = 3); KIF1A (n = 2); and one each of SPAST, ATL1, SPG7, PCYT2, PSEN1, ATXN1, ALDH18A1, CYP7B1, and RFT1. Structural variants in SPAST, SPG11, SPG7, MFN2, MPZ, KIF5A, and GJB1 were excluded by computational prediction and manual visualisation. In this preliminary cohort screening panel of disease genes using WES/WGS data, we solved ~50% of cases, which is similar to diagnostic yields reported for global cohorts. However, the mutational profile among South Africans with GN and HSP differs substantially from that in the Global North.

Splicing defects in rare diseases: transcriptomics and machine learning strategies towards genetic diagnosis.

Genomic variants affecting pre-messenger RNA splicing and its regulation are known to underlie many rare genetic diseases. However, common workflows for genetic diagnosis and clinical variant interpretation frequently overlook splice-altering variants. To better serve patient populations and advance biomedical knowledge, it has become increasingly important to develop and refine approaches for detecting and interpreting pathogenic splicing variants. In this review, we will summarize a few recent developments and challenges in using RNA sequencing technologies for rare disease investigation. Moreover, we will discuss how recent computational splicing prediction tools have emerged as complementary approaches for revealing disease-causing variants underlying splicing defects. We speculate that continuous improvements to sequencing technologies and predictive modeling will not only expand our understanding of splicing regulation but also bring us closer to filling the diagnostic gap for rare disease patients.

Novel homozygous variants in PRORP expand the genotypic spectrum of combined oxidative phosphorylation deficiency 54

Biallelic hypomorphic variants in PRORP have been recently described as causing the autosomal recessive disorder combined oxidative phosphorylation deficiency type 54 (COXPD54). COXPD54 encompasses a phenotypic spectrum of sensorineural hearing loss and ovarian insufficiency (Perrault syndrome) to leukodystrophy. Here, we report three additional families with homozygous missense PRORP variants with pleiotropic phenotypes. Each missense variant altered a highly conserved residue within the metallonuclease domain. In vitro mitochondrial tRNA processing assays with recombinant TRMT10C, SDR5C1 and PRORP indicated two COXPD54-associated PRORP variants, c.1159A>G (p.Thr387Ala) and c.1241C>T (p.Ala414Val), decreased pre-tRNAIle cleavage, consistent with both variants impacting tRNA processing. No significant decrease in tRNA processing was observed with PRORP c.1093T>C (p.Tyr365His), which was identified in an individual with leukodystrophy. These data provide independent evidence that PRORP variants are associated with COXPD54 and that the assessment of 5′ leader mitochondrial tRNA processing is a valuable assay for the functional analysis and clinical interpretation of novel PRORP variants.

Cross-protein transfer learning substantially improves disease variant prediction

BackgroundGenetic variation in the human genome is a major determinant of individual disease risk, but the vast majority of missense variants have unknown etiological effects. Here, we present a robust learning framework for leveraging saturation mutagenesis experiments to construct accurate computational predictors of proteome-wide missense variant pathogenicity.ResultsWe train cross-protein transfer (CPT) models using deep mutational scanning (DMS) data from only five proteins and achieve state-of-the-art performance on clinical variant interpretation for unseen proteins across the human proteome. We also improve predictive accuracy on DMS data from held-out proteins. High sensitivity is crucial for clinical applications and our model CPT-1 particularly excels in this regime. For instance, at 95% sensitivity of detecting human disease variants annotated in ClinVar, CPT-1 improves specificity to 68%, from 27% for ESM-1v and 55% for EVE. Furthermore, for genes not used to train REVEL, a supervised method widely used by clinicians, we show that CPT-1 compares favorably with REVEL. Our framework combines predictive features derived from general protein sequence models, vertebrate sequence alignments, and AlphaFold structures, and it is adaptable to the future inclusion of other sources of information. We find that vertebrate alignments, albeit rather shallow with only 100 genomes, provide a strong signal for variant pathogenicity prediction that is complementary to recent deep learning-based models trained on massive amounts of protein sequence data. We release predictions for all possible missense variants in 90% of human genes.ConclusionsOur results demonstrate the utility of mutational scanning data for learning properties of variants that transfer to unseen proteins.