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Background: The international study ThromboGenomics has evaluated the diagnostic rate using a targeted multigene panel test for the screening of inherited bleeding, thrombotic and platelet disorders., Objectives: We retrospectively analyzed the results of the implementation of genetic testing for inherited bleeding, thrombotic and platelet disorders in Belgian clinical practice and evaluated possible reclassification of reported variants., Patients/methods: We implemented a Thrombosis-Hemostasis multigene panel test using whole exome sequencing to diagnose 487 patients recruited by 27 different Belgian hospitals with the implementation of stringent laboratory accreditation standards and by studying up to 100 diagnostic-grade genes., Results: This Thrombosis-Hemostasis multigene panel test was able to detect at least one genetic variant in 58% of the 487 patients of which 50% were (likely) pathogenic variants and the others were variants of unknown significance. Polygenic variants were detected in 65 patients (13%). A multi-step workflow for results discussion by multidisciplinary team meetings and patients' recalls for segregation studies and additional laboratory testing was set up. Variants were also submitted to the GoldVariants database from the International Society on Thrombosis and Haemostasis (ISTH). The aim of these approaches is to optimize variant interpretation and to (re)classify variants of unknown significance as (likely) pathogenic or (likely) benign., Conclusions: The growing implementation of multigene panel tests in clinical diagnostics comes with difficulties in interpreting genetic results. Additional efforts are needed to continuously optimize the diagnostic outcome., Competing Interests: Declaration of competing interest All authors declare they have no conflict of interest to disclose., (Copyright © 2022 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Purpose: Stringent variant interpretation guidelines can lead to high rates of variants of uncertain significance (VUS) for genetically heterogeneous disease like long QT syndrome (LQTS) and Brugada syndrome (BrS). Quantitative and disease-specific customization of American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines can address this false negative rate., Methods: We compared rare variant frequencies from 1847 LQTS (KCNQ1/KCNH2/SCN5A) and 3335 BrS (SCN5A) cases from the International LQTS/BrS Genetics Consortia to population-specific gnomAD data and developed disease-specific criteria for ACMG/AMP evidence classes-rarity (PM2/BS1 rules) and case enrichment of individual (PS4) and domain-specific (PM1) variants., Results: Rare SCN5A variant prevalence differed between European (20.8%) and Japanese (8.9%) BrS patients (p = 5.7 × 10 -18 ) and diagnosis with spontaneous (28.7%) versus induced (15.8%) Brugada type 1 electrocardiogram (ECG) (p = 1.3 × 10 -13 ). Ion channel transmembrane regions and specific N-terminus (KCNH2) and C-terminus (KCNQ1/KCNH2) domains were characterized by high enrichment of case variants and >95% probability of pathogenicity. Applying the customized rules, 17.4% of European BrS and 74.8% of European LQTS cases had (likely) pathogenic variants, compared with estimated diagnostic yields (case excess over gnomAD) of 19.2%/82.1%, reducing VUS prevalence to close to background rare variant frequency., Conclusion: Large case-control data sets enable quantitative implementation of ACMG/AMP guidelines and increased sensitivity for inherited arrhythmia genetic testing.

The application of next-generation sequencing to fetal pathology has proved to increase the diagnostic yield in fetuses with abnormal ultrasounds. We retrospectively reviewed genetic data of 30 selected cases studied through targeted resequencing of OMIM genes. In our experience, clinical data proved to be essential to support diagnostic reasoning and enhance variants' assessment. The molecular diagnosis was reached in 19/30 (63%) cases. Only in 7/19 cases the molecular diagnosis confirmed the initial diagnostic hypothesis, showing the relevance of the genotype-first approach. According to the genotype-phenotype correlation, we were able to divide the solved cases into three groups: i) the correlation is well established but it was missed due to lack of specificity, unusual presentation or recent description; ii) the clinical presentation is much more severe than currently known for the underlying condition; iii) the correlation does not recapitulate the entire phenotype, possibly due to the fetal presentation or multiple coexisting conditions. Moreover, we found a higher proportion of recessive diagnosis in abnormal fetuses compared to cohorts of individuals with developmental delay. Our findings suggest that fetal pathology may be enriched in rare alleles and/or in unusual combinations, counter-selected in postnatal genomes and thus contributing to both phenotypic extremeness and atypical presentation., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Knowledge on the influence of specific genotypes on the phenotypic expression of hypertrophic cardiomyopathy (HCM) is emerging. The objective of this study was to evaluate the genotype-phenotype relation in HCM patients and to construct a score to predict the genetic yield based to improve counseling. Unrelated HCM patients who underwent genetic testing were included in the analysis. Multivariate logistic regression was performed to identify variables that predict a positive genetic test. A weighted score was constructed based on the odds ratios. In total, 378 HCM patients were included of whom 141 carried a mutation (global yield 37%), 181 were mutation negative and 56 only carried a variant of unknown significance. We identified age at diagnosis <45 years, familial HCM, familial sudden death, arrhythmic syncope, maximal wall thickness ≥20 mm, asymmetrical hypertrophy and the absence of negative T waves in the lateral ECG leads as significant predictors of a positive genetic test. When we included these values in a risk score we found very high correlation between the score and the observed genetic yield (Pearson r = 0.98). MYBPC3 mutation carriers more frequently suffered sudden cardiac death compared to troponin complex mutations carriers (p = 0.01) and a similar trend was observed compared to MYH7 mutation carriers (p = 0.08) and mutation negative patients (p = 0.11). To conclude, a simple score system based on clinical variables can predict the genetic yield in HCM index patients, aiding in counseling HCM patients. MYBPC3 mutation carriers had a worse outcome regarding sudden cardiac death., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

Pathogenic variants in the BCAP31 gene have recently been associated with a severe congenital neurological phenotype, named DDCH after its key features: deafness, dystonia and central hypomyelination. BCAP31 is located at the Xq28 chromosomal region and only male individuals are currently known to be affected, the pathogenic variant being usually transmitted by healthy mothers. Here, we describe a three-year-old male child referred for severe developmental delay, failure to thrive, hearing loss and dyskinetic movements. After a conventional diagnostic workflow, including a normal array-CGH, a tentative diagnosis of dyskinetic cerebral palsy was retained. Clinical exome sequencing in the trio identified a small intragenic deletion in exon 8 of BCAP31, c.709&#95;721del (p.Val237Trpfs*69), originated de novo and not previously reported. Based on the ACMG variant classification, this variant is predicted to be 'likely pathogenic'. Given the consistent phenotypical overlap with the subjects already ascertained with DDCH, we considered this variant to be clinically relevant for this child and causative of his condition., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)

Left ventricular non-compaction (cardiomyopathy) (LVN(C)) is a rare hereditary cardiac condition, resulting from abnormal embryonic myocardial development. While it mostly occurs as an isolated condition, association with other cardiovascular manifestations such as Ebstein anomaly (EA) has been reported. This congenital heart defect is characterized by downward displacement of the tricuspid valve and leads to diminished ventricular size and function. In an autosomal dominant LVN(C) family consisting of five affected individuals, of which two also presented with EA and three with mitral valve insufficiency, we pursued the genetic disease cause using whole exome sequencing (WES). WES revealed a missense variant (p.Leu113Val) in TPM1 segregating with the LVN(C) phenotype. TPM1 encodes α-tropomyosin, which is involved in myocardial contraction, as well as in stabilization of non-muscle cytoskeletal actin filaments. So far, LVN(C)-EA has predominantly been linked to pathogenic variants in MYH7. However, one sporadic LVN(C)-EA case with a de novo TPM1 variant has recently been described. We here report the first LVN(C)-EA family segregating a pathogenic TPM1 variant, further establishing the association between EA predisposition and TPM1-related LVN(C). Consequently, we recommend genetic testing for both MYH7 and TPM1 in patients or families in which LVN(C)/non-compaction and EA coincide., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)

Background: Long QT syndrome (LQTS) is characterized by reduced penetrance and variable QT prolongation over time, resulting in an estimate of 25% carriers of a pathogenic mutation with a normal corrected QT (QTc) interval on the resting electrocardiogram (ECG)., Objective: The purpose of this study was to test the hypothesis that an individualized corrected QT interval derived from 24-hour Holter data more accurately predicts carriage of a pathogenic LQTS mutation than did QT derived from a standard 12-lead ECG and corrected using the Bazett formula (QTc interval)., Methods: Carriers of a pathogenic LQTS mutation and their genotype-negative family members who had both resting ECG and Holter recordings available were included. Automated and manual measurements of QTc were performed. QTi was derived from 24-hour Holter recordings and defined as the QT value at the intersection of an RR interval of 1000 ms, with the linear regression line fitted through QT-RR data points of each individual patient., Results: In total, 69 patients with LQTS (23 long QT type 1, 39 long QT type 2, and 7 long QT type 3) and 55 controls were selected. Demographic characteristics were comparable. A comparison of the receiver operating characteristic curves indicates that the test added diagnostic value compared to manual measurement (P = .02) or automated measurement (P = .005). The diagnostic accuracy of manually measured QTc using conventional cutoff criteria was 72%, while it was 92% using a sex-independent QTi cutoff of 445 ms. This was caused by a 39% increase in sensitivity without compromising the specificity., Conclusion: QTi derived from Holter recordings is superior to conventional QTc measured from a standard 12-lead ECG in predicting the mutation carrier state in families with LQTS., (Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Two siblings from consanguineous parents of Turkish descent presented with isolated dilated cardiomyopathy, leading to early death in infancy. The diagnosis of mitogenic cardiomyopathy was made histologically., Methods and Results: Linkage analysis combined with exome sequencing identified a homozygous deleterious mutation in the ALMS1 gene as the cause of this phenotype., Conclusions: Alström syndrome is characterized by a typically transient dilating cardiomyopathy in infancy, suggesting that mitogenic cardiomyopathy represents the extreme phenotype, resulting in demise before the other clinical symptoms become evident. This observation further illustrates the role of ALMS1 and cell cycle regulation., (Copyright © 2014. Published by Elsevier Masson SAS.)

Apert syndrome (OMIM 101200) is a rare genetic condition characterized by craniosynostosis and syndactyly of hands and feet with clinical variability. Two single nucleotides mutations in the linker region between the immunoglobulin-like domains II and IIIa of the ectodomainin the Fibroblast Growth Factor Receptor 2 gene (FGFR2, OMIM 176943) are responsible of the vast majority of cases: c.755C > G; p.Ser252Trp (65%) and c.758C > G; p.Pro253Arg (34%. Three exceptional cases carry multiple substitutions of adjacent nucleotides in the linker region. Here we present a Congolese male patient and his mother, both affected with Apert syndrome of variable severity, carrying a previously undescribed heterozygous mutation of three consecutive nucleotides (c.756&#95;758delGCCinsCTT) in the IgII-IgIIIa linker region. This is the fourth live-born patient to carry a multiple nucleotide substitution in the linker region and is the second alternative amino acid substitutions of the Pro253. Remarkably, this novel mutation was detected in the first Central African patient ever to be tested molecularly for the Apert syndrome. To discriminate between a hitherto unreported mutation and an ethnic specific polymorphism, we tested 105 Congolese controls, and no variation was detected., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)