Clinical Validation of Tagmentation-Based Genome Sequencing for Germline Disorders.

Genome sequencing (GS) is a powerful clinical tool used for the comprehensive diagnosis of germline disorders. GS library preparation typically involves mechanical DNA fragmentation, end repair, and bead-based library size selection followed by adapter ligation, which can require a large amount of input genomic DNA. Tagmentation using bead-linked transposomes can simplify the library preparation process and reduce the DNA input requirement. Here we describe the clinical validation of tagmentation-based PCR-free GS as a clinical test for rare germline disorders. Compared with the Genome-in-a-Bottle Consortium benchmark variant sets, GS had a recall >99.7% and a precision of 99.8% for single nucleotide variants and small insertion-deletions. GS also exhibited 100% sensitivity for clinically reported sequence variants and the copy number variants examined. Furthermore, GS detected mitochondrial sequence variants above 5% heteroplasmy and showed reliable detection of disease-relevant repeat expansions and SMN1 homozygous loss. Our results indicate that while lowering DNA input requirements and reducing library preparation time, GS enables uniform coverage across the genome as well as robust detection of various types of genetic alterations. With the advantage of comprehensive profiling of multiple types of genetic alterations, GS is positioned as an ideal first-tier diagnostic test for germline disorders.

Alström syndrome caused by maternal uniparental disomy.

Purpose: To describe a case of Alström syndrome arising from maternal uniparental disomy. Observations: A 13-month-old boy with poor vision and nystagmus was diagnosed with Alström syndrome based on genetic testing that identified a homozygous pathogenic variant, ALMS1 c.2141_2141del (p.Ser714Tyrfs*6), that was only found in his mother and not his father. In contrast to the usual autosomal recessive inheritance pattern in which a child inherits a variant from each parent, multi-step genetic testing of the child and both parents confirmed uniparental disomy as the mechanism of inheritance. Conclusions and Importance: Confirmation of uniparental disomy in autosomal recessive disorders allows for parental assurance that future offspring will be unaffected.

Aminoglycoside induced ototoxicity risk in the cystic fibrosis population: The utility of large-scale screening.

BACKGROUND: MT-RNR1 variants are a well-known cause of aminoglycoside-induced hearing loss (AIHL). Individuals with cystic fibrosis (CF) routinely receive aminoglycosides and are at high risk of AIHL. However, genetic testing before treatment is not routinely performed due to perceived rarity of risk, and cost ineffectiveness with traditional technologies. AIM: Assess the utility of large-scale screening for AIHL risk in the CF population, using digital droplet polymerase chain reaction (ddPCR), a novel and scalable low-cost molecular technique. METHODS: Using a clinically validated ddPCR assay, we performed retrospective testing on 122 and prospective testing on 32 individuals with CF for the two most common pathogenic variants associated with AIHL, MT-RNR1 m.1555 A > G and m.1494 C > T. Our study screened the largest known cohort of pediatric cases of CF (94/154) for these specific alterations. RESULTS: We identified two individuals positive for MT-RNR1 m.1555 A > G and no positives for m.1494 C > T. Of 32 prospective cases, 17 had aminoglycoside exposure. The positive case in our prospective group recently began inhaled tobramycin and denied hearing issues. The clinician adjusted to care for both the patient and sibling with CF (not included in cohort) who is presumed positive for m.1555 A > G due to the nature of mitochondrial inheritance. CONCLUSION: Our findings demonstrate the utility of pretreatment screening in the cystic fibrosis population for AIHL risk using ddPCR, a scalable and robust testing methodology at a fraction of the cost as compared to other sequencing-based methods. Therefore, the use of large-scale screening for AIHL risk in the cystic fibrosis community should be re-visited.

Best practices for the interpretation and reporting of clinical whole genome sequencing.

Whole genome sequencing (WGS) shows promise as a first-tier diagnostic test for patients with rare genetic disorders. However, standards addressing the definition and deployment practice of a best-in-class test are lacking. To address these gaps, the Medical Genome Initiative, a consortium of leading health care and research organizations in the US and Canada, was formed to expand access to high quality clinical WGS by convening experts and publishing best practices. Here, we present best practice recommendations for the interpretation and reporting of clinical diagnostic WGS, including discussion of challenges and emerging approaches that will be critical to harness the full potential of this comprehensive test.

P2T2: Protein Panoramic annoTation Tool for the interpretation of protein coding genetic variants.

MOTIVATION: Genomic data are prevalent, leading to frequent encounters with uninterpreted variants or mutations with unknown mechanisms of effect. Researchers must manually aggregate data from multiple sources and across related proteins, mentally translating effects between the genome and proteome, to attempt to understand mechanisms. MATERIALS AND METHODS: P2T2 presents diverse data and annotation types in a unified protein-centric view, facilitating the interpretation of coding variants and hypothesis generation. Information from primary sequence, domain, motif, and structural levels are presented and also organized into the first Paralog Annotation Analysis across the human proteome. RESULTS: Our tool assists research efforts to interpret genomic variation by aggregating diverse, relevant, and proteome-wide information into a unified interactive web-based interface. Additionally, we provide a REST API enabling automated data queries, or repurposing data for other studies. CONCLUSION: The unified protein-centric interface presented in P2T2 will help researchers interpret novel variants identified through next-generation sequencing. Code and server link available at github.com/GenomicInterpretation/p2t2.

Disease-specific ACMG/AMP guidelines improve sequence variant interpretation for hearing loss.

PURPOSE: The ClinGen Variant Curation Expert Panels (VCEPs) provide disease-specific rules for accurate variant interpretation. Using the hearing loss-specific American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines, the Hearing Loss VCEP (HL VCEP) illustrates the utility of expert specifications in variant interpretation. METHODS: A total of 157 variants across nine HL genes, previously submitted to ClinVar, were curated by the HL VCEP. The curation process involved collecting published and unpublished data for each variant by biocurators, followed by bimonthly meetings of an expert curation subgroup that reviewed all evidence and applied the HL-specific ACMG/AMP guidelines to reach a final classification. RESULTS: Before expert curation, 75% (117/157) of variants had single or multiple variants of uncertain significance (VUS) submissions (17/157) or had conflicting interpretations in ClinVar (100/157). After applying the HL-specific ACMG/AMP guidelines, 24% (4/17) of VUS and 69% (69/100) of discordant variants were resolved into benign (B), likely benign (LB), likely pathogenic (LP), or pathogenic (P). Overall, 70% (109/157) variants had unambiguous classifications (B, LB, LP, P). We quantify the contribution of the HL-specified ACMG/AMP codes to variant classification. CONCLUSION: Expert specification and application of the HL-specific ACMG/AMP guidelines effectively resolved discordant interpretations in ClinVar. This study highlights the utility of ClinGen VCEPs in supporting more consistent clinical variant interpretation.

Impact of integrated translational research on clinical exome sequencing.

PURPOSE: Exome sequencing often identifies pathogenic genetic variants in patients with undiagnosed diseases. Nevertheless, frequent findings of variants of uncertain significance necessitate additional efforts to establish causality before reaching a conclusive diagnosis. To provide comprehensive genomic testing to patients with undiagnosed disease, we established an Individualized Medicine Clinic, which offered clinical exome testing and included a Translational Omics Program (TOP) that provided variant curation, research activities, or research exome sequencing. METHODS: From 2012 to 2018, 1101 unselected patients with undiagnosed diseases received exome testing. Outcomes were reviewed to assess impact of the TOP and patient characteristics on diagnostic rates through descriptive and multivariate analyses. RESULTS: The overall diagnostic yield was 24.9% (274 of 1101 patients), with 174 (15.8% of 1101) diagnosed on the basis of clinical exome sequencing alone. Four hundred twenty-three patients with nondiagnostic or without access to clinical exome sequencing were evaluated by the TOP, with 100 (9% of 1101) patients receiving a diagnosis, accounting for 36.5% of the diagnostic yield. The identification of a genetic diagnosis was influenced by the age at time of testing and the disease phenotype of the patient. CONCLUSION: Integration of translational research activities into clinical practice of a tertiary medical center can significantly increase the diagnostic yield of patients with undiagnosed disease.

Expansion of PURA-Related Phenotypes and Discovery of a Novel PURA Variant: A Case Report.

Variants in PURA have recently been associated with an autosomal dominant form of PURA-related neurodevelopmental disorders. Using whole exome sequencing, patients with neurological phenotypes including hypotonia, developmental delay, learning disabilities, and seizures were identified to have de novo variants in PURA. We describe a proband with features similar to the previously described cases with PURA variants, but including additional features, such as short stature, delayed bone age, and delayed puberty. Exome sequencing revealed a novel pathogenic nonsense variant, c.190A>T (p.Lys64*; NM_005859), in PURA that was not inherited from the proband's mother. In the recent literature, a significant number of patients with variants in PURA have been described, but to our knowledge, none of these patients have the delayed bone age and growth plateau observed in the proband. It is therefore possible that the above PURA variant may be responsible for the novel features and thus expands the PURA-related phenotype spectrum.

Limited diagnostic impact of duplications <1 Mb of uncertain clinical significance: a 10-year retrospective analysis of reporting practices at the Mayo Clinic.

PURPOSE: Copy-number variants (CNVs) of uncertain clinical significance are routinely reported in a clinical setting only when exceeding predetermined reporting thresholds, typically based on CNV size. Given that very few genes are associated with triplosensitive phenotypes, it is not surprising that many interstitial duplications <1 Mb are found to be inherited and anticipated to be of limited or no clinical significance. METHODS: In an effort to further refine our reporting criteria to maximize diagnostic yield while minimizing the return of uncertain variants, we performed a retrospective analysis of all clinical microarray cases reported in a 10-year window. A total of 1112 reported duplications had parental follow-up, and these were compared by size, RefSeq gene content, and inheritance pattern. De novo origin was used as a rough proxy for pathogenicity. RESULTS: Approximately 6% of duplications 500 kb-1 Mb were de novo observations, compared with approximately 14% for 1-2 Mb duplications (p = 0.0005). On average, de novo duplications had higher gene counts than inherited duplications. CONCLUSION: Our data reveal limited diagnostic utility for duplications of uncertain significance <1 Mb. Considerations for revised reporting criteria are discussed and are applicable to CNVs detected by any genome-wide exploratory methodology, including exome/genome sequencing.

Development and Validation of a Next-Generation Sequencing Panel for Syndromic and Nonsyndromic Hearing Loss.

BACKGROUND: Deafness and hearing loss are common conditions that can be seen independently or as part of a syndrome and are often mediated by genetic causes. We sought to develop and validate a hereditary hearing loss panel (HHLP) to detect single nucleotide variants (SNVs), insertions and deletions (indels), and copy number variants (CNVs) in 166 genes related to nonsyndromic and syndromic hearing loss. METHODS: We developed a custom-capture next-generation sequencing (NGS) reagent to detect all coding regions, ±10 flanking bp, for the 166 genes related to nonsyndromic and syndromic hearing loss. Our validation consisted of testing 52 samples to establish accuracy, reproducibility, and analytical sensitivity. In addition to NGS, supplementary methods, including multiplex ligation-dependent probe amplification, long-range PCR, and Sanger sequencing, were used to ensure coverage of regions that had high complexity or homology. RESULTS: We observed 100% positive and negative percentage agreement for detection of SNVs (n = 362), small indels (1-22 bp, n = 25), and CNVs (gains, n = 8; losses, n = 17). Finally, we showed that this assay was able to detect variants with a variant allele frequency ≥20% for SNVs and indels and ≥30% to 35% for CNVs. CONCLUSIONS: We validated an HHLP that detects SNVs, indels, and CNVs in 166 genes related to syndromic and nonsyndromic hearing loss. The results of this assay can be utilized to confirm a diagnosis of hearing loss and related syndromic disorders associated with known causal genes.

First Report of Bilateral External Auditory Canal Cochlin Aggregates ("Cochlinomas") with Multifocal Amyloid-Like Deposits, Associated with Sensorineural Hearing Loss and a Novel Genetic Variant in COCH Encoding Cochlin.

Pathogenic variants in COCH, encoding cochlin, cause DFNA9 deafness disorder with characteristic histopathologic findings of cochlin deposits in the inner and middle ears. Here, we present the first case of deafness associated with bilateral external auditory canal (EAC) cochlin deposits, previously unreported evidence suggestive of cochlin-derived amyloid formation, and a novel COCH variant. A 54-year-old woman presented with progressive sensorineural hearing loss and bilateral EAC narrowing by subcutaneous thickening. Excision and histologic evaluation of tissue from both EACs showed paucicellular eosinophilic aggregates containing multiple Congo red-positive foci with yellow and green birefringence under crossed polarization light microscopy. Mass spectrometry performed on both the Congo red-positive and Congo red-negative areas identified cochlin as the most abundant protein, as well as a low abundance of universal amyloid signature peptides only in the Congo red-positive areas. Peptides indicative of a canonical amyloid type were not detected. Electron microscopy showed haphazard, branched microfibrils (3-7 nm in diameter) consistent with cochlin, as well as swirling fibrils (10-24 nm in diameter) reminiscent of amyloid fibrils. Cochlin immunohistochemical staining showed positivity throughout the aggregates. Sequencing of the entire COCH gene coding region from the patient's blood revealed a novel variant resulting in a non-conservative amino acid substitution of isoleucine to phenylalanine (c.1621A>T, p.I541F) in the vWFA2 domain at the protein's C-terminus. Our findings reveal a new pathologic manifestation of cochlin, raise the possibility of previously undescribed cochlin-derived amyloid formation, and highlight the importance of thoroughly investigating all aggregative tissue findings in the practice of diagnostic pathology.

Type 8 long QT syndrome: pathogenic variants in CACNA1C-encoded Cav1.2 cluster in STAC protein binding site.

AIMS: Pathogenic gain-of-function variants in CACAN1C cause type-8 long QT syndrome (LQT8). We sought to describe the electrocardiographic features in LQT8 and utilize molecular modelling to gain mechanistic insights into its genetic culprits. METHODS AND RESULTS: Rare variants in CACNA1C were identified from genetic testing laboratories. Treating physicians provided clinical information. Variant pathogenicity was independently assessed according to recent guidelines. Pathogenic (P) and likely pathogenic (LP) variants were mapped onto a 3D modelled structure of the Cav1.2 protein. Nine P/LP variants, identified in 23 patients from 19 families with non-syndromic LQTS were identified. Six variants, found in 79% of families, clustered to a 4-residue section in the cytosolic II-III loop region which forms a region capable of binding STAC SH3 domains. Therefore, variants may affect binding of SH3-domain containing proteins. Arrhythmic events occurred in similar proportions of patients with II-III loop variants and with other P/LP variants (53% vs. 48%, P = 0.41) despite shorter QTc intervals (477 ± 31 ms vs. 515 ± 37 ms, P = 0.03). A history of sudden death was reported only in families with II-III loop variants (60% vs. 0%, P = 0.03). The predominant T-wave morphology was a late peaking T wave with a steep descending limb. Exercise testing demonstrated QTc prolongation on standing and at 4 min recovery after exercise. CONCLUSION: The majority of P/LP variants in patients with CACNA1C-mediated LQT8 cluster in an SH3-binding domain of the cytosolic II-III loop. This represents a 'mutation hotspot' in LQT8. A late-peaking T wave with a steep descending limb and QT prolongation on exercise are commonly seen.

Expert specification of the ACMG/AMP variant interpretation guidelines for genetic hearing loss.

Due to the high genetic heterogeneity of hearing loss (HL), current clinical testing includes sequencing large numbers of genes, which often yields a significant number of novel variants. Therefore, the standardization of variant interpretation is crucial to provide consistent and accurate diagnoses. The Hearing Loss Variant Curation Expert Panel was created within the Clinical Genome Resource to provide expert guidance for standardized genomic interpretation in the context of HL. As one of its major tasks, our Expert Panel has adapted the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines for the interpretation of sequence variants in HL genes. Here, we provide a comprehensive illustration of the newly specified ACMG/AMP HL rules. Three rules remained unchanged, four rules were removed, and the remaining 21 rules were specified. These rules were further validated and refined using a pilot set of 51 variants assessed by curators and disease experts. Of the 51 variants evaluated in the pilot, 37% (19/51) changed category based upon application of the expert panel specified rules and/or aggregation of evidence across laboratories. These HL-specific ACMG/AMP rules will help standardize variant interpretation, ultimately leading to better care for individuals with HL.

Developmental delay and failure to thrive associated with a loss-of-function variant in WHSC1 (NSD2).

Wolf-Hirschhorn syndrome (WHS) is a microdeletion syndrome characterized by distinctive facial features consisting of "Greek warrior helmet" appearance, prenatal and postnatal growth deficiency, developmental disability, and seizures. This disorder is caused by heterozygous deletions on chromosome 4p16.3 often identified by cytogenetic techniques. Many groups have attempted to identify the critical region within this deletion to establish which genes are responsible for WHS. Herein, clinical whole exome sequencing (WES) was performed on a child with developmental delays, mild facial dysmorphisms, short stature, failure to thrive, and microcephaly, and revealed a de novo frameshift variant, c.1676_1679del (p.Arg559Tfs*38), in WHSC1 (NSD2). While WHSC1 falls within the WHS critical region, individuals with only disruption of this gene have only recently been described in the literature. Loss-of-function de novo variations in WHSC1 were identified in large developmental delay, autism, diagnostic, and congenital cardiac cohorts, as well as recent case reports, suggesting that de novo loss-of-function WHSC1 variants may be related to disease. These findings, along with our patient suggest that loss-of-function variation in WHSC1 may lead to a mild form of Wolf-Hirschhorn syndrome, and also may suggest that the developmental delays, facial dysmorphisms, and short stature seen in WHS may be due to disruption of WHSC1 gene.

Characterization of three ciliopathy pedigrees expands the phenotype associated with biallelic C2CD3 variants.

Whole exome sequencing (WES) is utilized in diagnostic odyssey cases to identify the underlying genetic cause associated with complex phenotypes. Recent publications suggest that WES reveals the genetic cause in ~25% of these cases and is most successful when applied to children with neurological disease. The residual 75% of cases remain genetically elusive until more information becomes available in the literature or functional studies are pursued. WES performed on three families with presumed ciliopathy diagnoses, including orofaciodigital (OFD) syndrome, fetal encephalocele, or Joubert-related disorder, identified compound heterozygous variants in C2CD3. Biallelic variants in C2CD3 have previously been associated with ciliopathies, including OFD syndrome type 14 (OFD14; MIM: 615948). As three of the six identified variants were predicted to affect splicing, exon-skipping analysis using either RNA sequencing or PCR-based methods were completed to determine the pathogenicity of these variants, and showed that each of the splicing variants led to a frameshifted protein product. Using these studies in combination with the 2015 ACMG guidelines, each of the six identified variants were classified as either pathogenic or likely pathogenic, and are therefore likely responsible for our patients' phenotypes. Each of the families had a distinct clinical phenotype and severity of disease, extending from lethal to viable. These findings highlight that there is a broad phenotypic spectrum associated with C2CD3-mediated disease and not all patients present with the typical features of OFD14.

De Novo DNM1L Variant in a Teenager With Progressive Paroxysmal Dystonia and Lethal Super-refractory Myoclonic Status Epilepticus.

BACKGROUND: The dynamin 1-like gene ( DNM1L) encodes a GTPase that mediates mitochondrial and peroxisomal fission and fusion. We report a new clinical presentation associated with a DNM1L pathogenic variant and review the literature. RESULTS: A 13-year-old boy with mild developmental delays and paroxysmal dystonia presented acutely with multifocal myoclonic super-refractory status epilepticus. Despite sustained and aggressive treatment, seizures persisted and care was ultimately withdrawn in the context of extensive global cortical atrophy. Rapid trio-whole exome sequencing revealed a de novo heterozygous c.1207C>T (p.R403C) pathogenic variant in DNM1L. Immunofluorescence staining of fibroblast mitochondria revealed abnormally elongated and tubular morphology. CONCLUSIONS: This case highlights the diagnostic importance of rapid whole exome sequencing within a critical care setting and reveals the expanding phenotypic spectrum associated with DNM1L variants. This now includes progressive paroxysmal dystonia and adolescent-onset super-refractory myoclonic status epilepticus contributing to strikingly rapid and progressive cortical atrophy and death.

Co-occurrence of a maternally inherited DNMT3A duplication and a paternally inherited pathogenic variant in EZH2 in a child with growth retardation and severe short stature: atypical Weaver syndrome or evidence of a DNMT3A dosage effect?

Overgrowth syndromes are a clinically heterogeneous group of disorders characterized by localized or generalized tissue overgrowth and varying degrees of developmental and intellectual disability. An expanding list of genes associated with overgrowth syndromes include the histone methyltransferase genes EZH2 and NSD1, which cause Weaver and Sotos syndrome, respectively, and the DNA methyltransferase (DNMT3A) gene that results in Tatton-Brown-Rahman syndrome (TBRS). Here, we describe a 5-year-old female with a paternally inherited pathogenic mutation in EZH2 (c.2050C>T, p.Arg684Cys) and a maternally inherited 505-kb duplication of uncertain significance at 2p23.3 (encompassing five genes, including DNMT3A) who presented with intrauterine growth restriction, slow postnatal growth, short stature, hypotonia, developmental delay, and neuroblastoma diagnosed at the age of 8 mo. Her father had tall stature, dysmorphic facial features, and intellectual disability consistent with Weaver syndrome, whereas her mother had short stature, cognitive delays, and chronic nonprogressive leukocytosis. It has been previously shown that EZH2 directly controls DNA methylation through physical association with DNMTs, including DNMT3A, with concomitant H3K27 methylation and CpG promoter methylation leading to repression of EZH2 target genes. Interestingly, NSD1 is involved in H3K36 methylation, a mark associated with transcriptional activation, and exhibits exquisite dosage sensitivity leading to overgrowth when deleted and severe undergrowth when duplicated in vivo. Although there is currently no evidence of dosage effects for DNMT3A, the co-occurrence of a duplication involving this gene and a pathogenic alteration in EZH2 in a patient with severe undergrowth is suggestive of a similar paradigm and further study is warranted.

Bi-allelic Alterations in AEBP1 Lead to Defective Collagen Assembly and Connective Tissue Structure Resulting in a Variant of Ehlers-Danlos Syndrome.

AEBP1 encodes the aortic carboxypeptidase-like protein (ACLP) that associates with collagens in the extracellular matrix (ECM) and has several roles in development, tissue repair, and fibrosis. ACLP is expressed in bone, the vasculature, and dermal tissues and is involved in fibroblast proliferation and mesenchymal stem cell differentiation into collagen-producing cells. Aebp1-/- mice have abnormal, delayed wound repair correlating with defects in fibroblast proliferation. In this study, we describe four individuals from three unrelated families that presented with a unique constellation of clinical findings including joint laxity, redundant and hyperextensible skin, poor wound healing with abnormal scarring, osteoporosis, and other features reminiscent of Ehlers-Danlos syndrome (EDS). Analysis of skin biopsies revealed decreased dermal collagen with abnormal collagen fibrils that were ragged in appearance. Exome sequencing revealed compound heterozygous variants in AEBP1 (c.1470delC [p.Asn490_Met495delins(40)] and c.1743C>A [p.Cys581∗]) in the first individual, a homozygous variant (c.1320_1326del [p.Arg440Serfs∗3]) in the second individual, and a homozygous splice site variant (c.1630+1G>A) in two siblings from the third family. We show that ACLP enhances collagen polymerization and binds to several fibrillar collagens via its discoidin domain. These studies support the conclusion that bi-allelic pathogenic variants in AEBP1 are the cause of this autosomal-recessive EDS subtype.