Genetic testing in motor neurone disease

A minority (10%–15%) of cases of amyotrophic lateral sclerosis (ALS), the most common form of motor neurone disease (MND), are currently attributable to pathological variants in a single identifiable gene. With the emergence of new therapies targeting specific genetic subtypes of ALS, there is an increasing role for routine genetic testing for all those with a definite diagnosis. However, potential harm to both affected individuals and particularly to asymptomatic relatives can arise from the indiscriminate use of genetic screening, not least because of uncertainties around incomplete penetrance and variants of unknown significance. The most common hereditary cause of ALS, an intronic hexanucleotide repeat expansion in C9ORF72, may be associated with frontotemporal dementia independently within the same pedigree. The boundary of what constitutes a possible family history of MND has therefore extended to include dementia and associated psychiatric presentations. Notwithstanding the important role of clinical genetics specialists, all neurologists need a basic understanding of the current place of genetic testing in MND, which holds lessons for other neurological disorders.

Clinical Spectrum of SCN5A Channelopathy in Children with Primary Electrical Disease and Structurally Normal Hearts

Sodium voltage-gated channel α subunit 5 (SCN5A)-mutations may cause an array of arrhythmogenic syndromes most frequently as an autosomal dominant trait, with incomplete penetrance, variable expressivity and male predominance. In the present study, we retrospectively describe a group of Mexican patients with SCN5A-disease causing variants in whom the onset of symptoms occurred in the pediatric age range. The study included 17 patients with clinical diagnosis of primary electrical disease, at least one SCN5A pathogenic or likely pathogenic mutation and age of onset <18 years, and all available first- and second-degree relatives. Fifteen patients (88.2%) were male, and sixteen independent variants were found (twelve missense, three truncating and one complex inframe deletion/insertion). The frequency of compound heterozygosity was remarkably high (3/17, 17.6%), with early childhood onset and severe disease. Overall, 70.6% of pediatric patients presented with overlap syndrome, 11.8% with isolated sick sinus syndrome, 11.8% with isolated Brugada syndrome (BrS) and 5.9% with isolated type 3 long QT syndrome (LQTS). A total of 24/45 SCN5A mutation carriers were affected (overall penetrance 53.3%), and penetrance was higher in males (63.3%, 19 affected/30 mutation carriers) than in females (33.3%, 5 affected/15 carriers). In conclusion, pediatric patients with SCNA-disease causing variants presented mainly as overlap syndrome, with predominant loss-of-function phenotypes of sick sinus syndrome (SSS), progressive cardiac conduction disease (PCCD) and ventricular arrhythmias.

Systems biology analysis of human genomes points to key pathways conferring spina bifida risk

Spina bifida (SB) is a debilitating birth defect caused by multiple gene and environment interactions. Though SB shows non-Mendelian inheritance, genetic factors contribute to an estimated 70% of cases. Nevertheless, identifying human mutations conferring SB risk is challenging due to its relative rarity, genetic heterogeneity, incomplete penetrance, and environmental influences that hamper genome-wide association studies approaches to untargeted discovery. Thus, SB genetic studies may suffer from population substructure and/or selection bias introduced by typical candidate gene searches. We report a population based, ancestry-matched whole-genome sequence analysis of SB genetic predisposition using a systems biology strategy to interrogate 298 case-control subject genomes (149 pairs). Genes that were enriched in likely gene disrupting (LGD), rare protein-coding variants were subjected to machine learning analysis to identify genes in which LGD variants occur with a different frequency in cases versus controls and so discriminate between these groups. Those genes with high discriminatory potential for SB significantly enriched pathways pertaining to carbon metabolism, inflammation, innate immunity, cytoskeletal regulation, and essential transcriptional regulation consistent with their having impact on the pathogenesis of human SB. Additionally, an interrogation of conserved noncoding sequences identified robust variant enrichment in regulatory regions of several transcription factors critical to embryonic development. This genome-wide perspective offers an effective approach to the interrogation of coding and noncoding sequence variant contributions to rare complex genetic disorders.

A spectrum of recessiveness among Mendelian disease variants in UK Biobank

Recent work has found increasing evidence of mitigated, incompletely penetrant phenotypes in heterozygous carriers of recessive Mendelian disease variants. We leveraged whole-exome imputation within the full UK Biobank cohort (N~500K) to extend such analyses to 3,481 rare variants curated from ClinVar and OMIM. Testing these variants for association with 57 quantitative traits yielded 103 significant associations involving variants previously implicated in 35 different diseases. Notable examples included a POR missense variant implicated in Antley-Bixler syndrome that associated with a 1.76 (s.e. 0.27) cm increase in height, and an ABCA3 missense variant implicated in interstitial lung disease that associated with reduced FEV1/FVC ratio. Association analyses with 1,257 disease traits yielded five additional variant-disease associations. We also observed contrasting levels of recessiveness between two more-common, classical Mendelian diseases. Carriers of cystic fibrosis variants exhibited increased risk of several mitigated disease phenotypes, whereas carriers of spinal muscular atrophy alleles showed no evidence of altered phenotypes. Incomplete penetrance of cystic fibrosis carrier phenotypes did not appear to be mediated by common allelic variation on the functional haplotype. Our results show that many disease-associated recessive variants can produce mitigated phenotypes in heterozygous carriers and motivate further work exploring penetrance mechanisms.

Histopathological Features and Protein Markers of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a heritable heart muscle disease characterized by syncope, palpitations, ventricular arrhythmias and sudden cardiac death (SCD) especially in young individuals. It is estimated to affect 1:5,000 individuals in the general population, with &gt;60% of patients bearing one or more mutations in genes coding for desmosomal proteins. Desmosomes are intercellular adhesion junctions, which in cardiac myocytes reside within the intercalated disks (IDs), the areas of mechanical and electrical cell-cell coupling. Histologically, ACM is characterized by fibrofatty replacement of cardiac myocytes predominantly in the right ventricular free wall though left ventricular and biventricular forms have also been described. The disease is characterized by age-related progression, vast phenotypic manifestation and incomplete penetrance, making proband diagnosis and risk stratification of family members particularly challenging. Key protein redistribution at the IDs may represent a specific diagnostic marker but its applicability is still limited by the need for a myocardial sample. Specific markers of ACM in surrogate tissues, such as the blood and the buccal epithelium, may represent a non-invasive, safe and inexpensive alternative for diagnosis and cascade screening. In this review, we shall cover the most relevant biomarkers so far reported and discuss their potential impact on the diagnosis, prognosis and management of ACM.

Arrhythmogenic Right Ventricular Cardiomyopathy in Pediatric Patients: An Important but Underrecognized Clinical Entity

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy characterized by fibrofatty infiltration of predominantly the right ventricular (RV) myocardium. Affected patients typically present as young adults with hemodynamically stable ventricular tachycardia, although pediatric cases are increasingly recognized. These young subjects often have a more severe phenotype with a high risk of sudden cardiac death (SCD) and progression toward heart failure. Diagnosis of ARVC is made by combining multiple sources of information as prescribed by the consensus-based Task Force Criteria. The description of Naxos disease, a fully penetrant autosomal recessive disorder that is associated with ARVC and a cutaneous phenotype of palmoplantar keratoderma and wooly hair facilitated the identification of the genetic cause of ARVC. At present, approximately 60% of patients are found to carry a pathogenic variant in one of five genes associated with the cardiac desmosome. The incomplete penetrance and variable expressivity of these variants however implies an important role for environmental factors, of which participation in endurance exercise is a strong risk factor. Since there currently is no definite cure for ARVC, disease management is directed toward symptom reduction, delay of disease progression, and prevention of SCD. This clinically focused review describes the spectrum of ARVC among children and adolescents, the genetic architecture underlying this disease, the cardio-cutaneous syndromes that led to its identification, and current diagnostic and therapeutic strategies in pediatric ARVC subjects.

527 An incidental diagnosis in a patient with SARS-CoV-2 pneumonia

Hypertrophic cardiomyopathy (HCM) is the most frequent genetic disease of the myocardium, with a prevalence of 1:500 cases in the general population. The salient feature is a hypertrophy, symmetrical or not, of the walls of the left ventricle (mainly the septum, but also less typical locations, such as the apex or the infero-lateral wall), not linked to abnormal load conditions. HCM is mostly an autosomal dominant inherited disease with incomplete penetrance and variable expressivity, mainly linked to mutations in genes coding for sarcomeric proteins. Several studies have shown an up-regulation of the ACE-2 gene, perhaps indicative of a compensatory anti-hypertrophic and anti-fibrotic response of the myocardium, in hypertrophic cardiomyopathy. Being the ACE-2 receptor target of the SARS-CoV-2 virus, these patients may have an increased risk of infection and a worse outcome. A 47-year-old man, with no known comorbidities, was hospitalized in our Emergency Medicine Department for bilateral SARS-CoV-2 pneumonia. Noninvasive mechanical ventilation c-PAP (FiO2 60%, PEEP 7.5 cmH2O) was started for hypoxemic respiratory failure and an ECG showed diffuse ventricular repolarization abnormalities suggestive of left overload (asymmetric negative T waves V4–V6, in I, II, and aVL, flat in aVF. Figure 1), with a deep Q wave in III. The patient was asymptomatic for chest pain and equivalents and D-dimer and indices of myocardionecrosis were normal. Echocardiographic evaluation was performed, with evidence of marked asymmetric concentric hypertrophy of the left ventricle (interventricular septum: 16 mm), without significant anomalies in segmental kinetics, noteworthy valvulopathies, and pericardial effusion. The family and personal medical history were negative for syncope, sudden cardiac death, and resuscitated cardiac arrest and the estimated risk of sudden cardiac death at 5 years (HCM Risk-SCD) was &lt;4% (1.33%). The diagnostic hypothesis of non-obstructive hypertrophic cardiomyopathy was advanced. During hospitalization, ECG monitoring showed no sustained ventricular arrhythmias and the patient remained asymptomatic for dyspnoea, chest pain, and equivalents. Subsequent echocardiograms showed no new changes. A progressive weaning from oxygen support was carried out and, after 30 days, the patient was discharged to home fiduciary isolation, with optimal cardiological therapy and indication to study with cardiac magnetic resonance to the negativization of the nasal swab for SARS-CoV-2. MRI, performed about 2 months later, confirmed the suspicion of hypertrophic cardiomyopathy, with no signs of late enhancement in T1-weighted sequences (Figure 2). The patient was then referred to a genetic study and cardiological follow-up, still in progress.

816 UNA Diagnosi . . . Incidentale

Hypertrophic cardiomyopathy (HCM) is the most frequent genetic disease of the myocardium, with a prevalence of 1:500 cases in the general population. The salient feature is a hypertrophy, symmetrical or not, of the walls of the left ventricle (mainly the septum, but also less typical locations, such as the apex or the infero-lateral wall), not linked to abnormal load conditions. HCM is mostly an autosomal dominant inherited disease with incomplete penetrance and variable expressivity, mainly linked to mutations in genes coding for sarcomeric proteins. Several studies have shown an up-regulation of the ACE-2 gene, perhaps indicative of a compensatory anti-hypertrophic and anti-fibrotic response of the myocardium, in hypertrophic cardiomyopathy. Being the ACE-2 receptor target of the Sars-CoV-2 virus, these patients may have an increased risk of infection and a worse outcome. A 47-year-old man, with no known comorbidities, was hospitalized in our Emergency Medicine Department for bilateral Sars-CoV-2 pneumonia. Noninvasive mechanical ventilation c-PAP (FiO2 60%, PEEP 7.5 cmH20) was started for hypoxemic respiratory failure and an ECG showed diffuse ventricular repolarization abnormalities suggestive of left overload (asymmetric negative T waves V4 to V6, in I, II and aVL, flat in aVF. Figure 1), with a deep Q wave in III. The patient was asymptomatic for chest pain and equivalents and D-dimer and indices of myocardionecrosis were normal. Echocardiographic evaluation was performed, with evidence of marked asymmetric concentric hypertrophy of the left ventricle (interventricular septum: 16 mm), without significant anomalies in segmental kinetics, noteworthy valvulopathies and pericardial effusion. The family and personal medical history were negative for syncope, sudden cardiac death and resuscitated cardiac arrest and the estimated risk of sudden cardiac death at five years (HCM Risk-SCD) was &lt;4% (1.33%). The diagnostic hypothesis of non-obstructive hypertrophic cardiomyopathy was advanced. During hospitalization, ECG monitoring showed no sustained ventricular arrhythmias and the patient remained asymptomatic for dyspnoea, chest pain and equivalents. Subsequent echocardiograms showed no new changes. A progressive weaning from oxygen support was carried out and, after thirty days, the patient was discharged to home fiduciary isolation, with optimal cardiological therapy and indication to study with cardiac magnetic resonance to the negativization of the nasal swab for Sars-CoV-2. MRI, performed about two months later, confirmed the suspicion of hypertrophic cardiomyopathy, with no signs of late enhancement in T1-weighted sequences (Figure 2). The patient was then referred to a genetic study and cardiological follow-up, still in progress. 816 Figure 1816 Figure 1

Inflammation and Immune Response in Arrhythmogenic Cardiomyopathy: State-of-the-Art Review

Arrhythmogenic cardiomyopathy (ACM) is a primary disease of the myocardium, predominantly caused by genetic defects in proteins of the cardiac intercalated disc, particularly, desmosomes. Transmission is mostly autosomal dominant with incomplete penetrance. ACM also has wide phenotype variability, ranging from premature ventricular contractions to sudden cardiac death and heart failure. Among other drivers and modulators of phenotype, inflammation in response to viral infection and immune triggers have been postulated to be an aggravator of cardiac myocyte damage and necrosis. This theory is supported by multiple pieces of evidence, including the presence of inflammatory infiltrates in more than two-thirds of ACM hearts, detection of different cardiotropic viruses in sporadic cases of ACM, the fact that patients with ACM often fulfill the histological criteria of active myocarditis, and the abundance of anti–desmoglein-2, antiheart, and anti-intercalated disk autoantibodies in patients with arrhythmogenic right ventricular cardiomyopathy. In keeping with the frequent familial occurrence of ACM, it has been proposed that, in addition to genetic predisposition to progressive myocardial damage, a heritable susceptibility to viral infections and immune reactions may explain familial clustering of ACM. Moreover, considerable in vitro and in vivo evidence implicates activated inflammatory signaling in ACM. Although the role of inflammation/immune response in ACM is not entirely clear, inflammation as a driver of phenotype and a potential target for mechanism-based therapy warrants further research. This review discusses the present evidence supporting the role of inflammatory and immune responses in ACM pathogenesis and proposes opportunities for translational and clinical investigation.

Expanding the Evidence of a Semi-Dominant Inheritance in GDF2 Associated with Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) sometimes co-exists with hereditary hemorrhagic telangiectasia (HHT). Despite being clinically diagnosable according to Curaçao criteria, HHT can be difficult to diagnose due to its clinically heterogenicity and highly overlapping with PAH. Genetic analysis of the associated genes ACVRL1, ENG, SMAD4 and GDF2 can help to confirm or discard the presumptive diagnosis. As part of the clinical routine and to establish a genetic diagnosis, we have analyzed a cohort of patients with PAH and overlapping HHT features through a customized Next Generation Sequencing (NGS) panel of 21 genes, designed and validated in-house. We detected a homozygous missense variant in GDF2 in a pediatric patient diagnosed with PAH associated with HHT and a missense variant along with a heterozygous deletion in another idiopathic PAH patient (compound heterozygous inheritance). In order to establish variant segregation, we analyzed all available family members. In both cases, parents were carriers for the variants, but neither was affected. Our results expand the clinical spectrum and the inheritance pattern associated with GDF2 pathogenic variants suggesting incomplete penetrance and/or variability of expressivity with a semi-dominant pattern of inheritance.