Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy (TMA) characterized by dysregulation of the alternative pathway of complement. Heterozygous variants in complement and complement regulatory proteins may increase risk for aHUS and, to date, the highest frequency of disease-causing variants in aHUS has been identified in the CFH gene encoding complement factor H. Clinical laboratory classification of variants identified in CFH can be challenging, particularly in the case of novel variants. In this report, we describe 6 patients with aHUS found to have rare variants in CFH and highlight challenges faced with variant classification in rare disorders such as aHUS.
Abstract Gonadotropin independent sexual precocity (SP) may be due to congenital adrenal hyperplasia (CAH), and its timing usually depends on the type of mutation in the
Background— Postmortem genetic testing for heritable cardiovascular (CV) disorders is often lacking because ideal specimens (ie, whole blood) are not retained routinely at autopsy. Formalin-fixed paraffin-embedded tissue (FFPET) is ubiquitously collected at autopsy, but DNA quality hampers its use with traditional sequencing methods. Targeted next-generation sequencing may offer the ability to circumvent such limitations, but a method has not been previously described. The primary aim of this study was to develop and evaluate the use of FFPET for heritable CV disorders via next-generation sequencing. Methods and Results— Nineteen FFPET (heart) and blood (whole blood or dried blood spot) specimens underwent targeted next-generation sequencing using a custom panel of 101 CV-associated genes. Nucleic acid yield and quality metrics were evaluated in relation to FFPET specimen age (6 months to 15 years; n=14) and specimen type (FFPET versus whole blood and dried blood spot; n=12). Four FFPET cases with a clinical phenotype of heritable CV disorder were analyzed. Accuracy and precision were 100% concordant between all sample types, with read depths >100× for most regions tested. Lower read depth, as low as 40×, was occasionally observed with FFPET and dried blood spot. High-quality DNA was obtained from FFPET samples as old as 15 years. Genomic analysis of FFPET from the 4 phenotype-positive/genotype unknown cases all revealed putative disease-causing variants. Conclusions— Similar performance characteristics were observed for next-generation sequencing of FFPET, whole blood, and dried blood spot in the evaluation of inherited CV disorders. Although blood is preferable for genetic analyses, this study offers an alternative when only FFPET is available.
Protein-truncating variants in the TTN gene are a well-established cause of dilated cardiomyopathy (DCM). We report a novel case of DCM caused by a mobile element insertion (MEI) in TTN, through which we highlight the key features of MEIs in next-generation sequencing data. Because of the rarity of MEIs, the next-generation sequencing data features associated with these events may be mistaken as noise, potentially leading to missed diagnoses. Next-generation sequencing gene panel testing for DCM was performed on a 17-year-old male patient presenting with severe left ventricular dilatation and systolic dysfunction. Manta was used for structural variant detection, followed by manual review of NGS data for potential structural variants. Manta detected a potential insertion in TTN. Manual review identified hallmark features consistent with a LINE-1 MEI. This finding was orthogonally confirmed by long-range polymerase chain reaction and gel electrophoresis, which indicated an insertion of approximately 4 to 5 kilobase pairs. The insertion disrupted the reading frame of TTN within an A-band exon, resulting in protein truncation that was classified as likely pathogenic. This case expands the mutational spectrum of TTN protein-truncating variants. It also underscores the importance of recognizing rarer types of pathogenic variants (eg, MEIs) to produce accurate genetic diagnostics.
Abstract PURPOSE Variants of uncertain significance (VUS) are a common result of diagnostic genetic testing and can be difficult to manage with potential misinterpretation and downstream costs, including time investment by clinicians. We investigated the rate of VUS reported on diagnostic testing via multi-gene panels (MGPs) and exome and genome sequencing (ES/GS) to measure the magnitude of uncertain results and explore ways to reduce their potentially detrimental impact. METHODS Rates of inconclusive results due to VUS were collected from over 1.5 million sequencing test results from 19 clinical laboratories in North America from 2020 - 2021. RESULTS We found a lower rate of inconclusive test results due to VUSs from ES/GS (22.5%) compared to MGPs (32.6%; p<0.0001). For MGPs, the rate of inconclusive results correlated with panel size. The use of trios reduced inconclusive rates (18.9% vs 27.6%; p<0.001) whereas the use of GS compared to ES had no impact (22.2% vs 22.6%; p=ns). CONCLUSION The high rate of VUS observed in diagnostic MGP testing warrants examining current variant reporting practices. We propose several approaches to reduce reported VUS rates, while directing clinician resources towards important VUS follow-up.
We report a 9-year-old Chinese girl with congenital thrombotic thrombocytopenic purpura found to be a compound heterozygote for 2 pathogenic variants in the ADAMTS13 gene, including a novel variation. The girl suffered from recurrent, life-threatening episodes of thrombocytopenia and hemolysis, and laboratory testing showed ADAMST13 enzyme activity of <5%. Sequencing of the ADAMTS13 gene revealed a previously reported missense variant, c.1787C>T (p.Ala596Val), and a novel duplication defined as c.1007_1025dup19 (p.Asp343Leufs*53); the duplication is predicted to result in a premature stop codon and protein truncation. We propose that this novel variant is partly responsible for the patient’s early-onset and severe phenotype.
