Clinical impact of re-evaluating genes and variants implicated in dilated cardiomyopathy.

PURPOSE: Accurate interpretation of variants detected in dilated cardiomyopathy (DCM) is crucial for patient care but has proven challenging. We applied a set of proposed refined American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) criteria for DCM, reclassified all detected variants in robust genes, and associated these results to patients' phenotype. METHODS: The study included 902 DCM probands from the Maastricht Cardiomyopathy Registry who underwent genetic testing. Two gene panel sizes (extended n = 48; and robust panel n = 14) and two standards of variant classification (standard versus the proposed refined ACMG/AMP criteria) were applied to compare genetic yield. RESULTS: A pathogenic or likely pathogenic (P/LP) variant was found in 17.8% of patients, and a variant of uncertain significance (VUS) was found in 32.8% of patients when using method 1 (extended panel (n = 48) + standard ACMG/AMP), compared to respectively 16.9% and 12.9% when using method 2 (robust panel (n = 14) + standard ACMG/AMP), and respectively 14% and 14.5% using method 3 (robust panel (n = 14) + refined ACMG/AMP). Patients with P/LP variants had significantly lower event-free survival compared to genotype-negative DCM patients. CONCLUSION: Stringent gene selection for DCM genetic testing reduced the number of VUS while retaining ability to detect similar P/LP variants. The number of genes on diagnostic panels should be limited to genes that have the highest signal to noise ratio.

A mutation update for the FLNC gene in myopathies and cardiomyopathies.

Filamin C (FLNC) variants are associated with cardiac and muscular phenotypes. Originally, FLNC variants were described in myofibrillar myopathy (MFM) patients. Later, high-throughput screening in cardiomyopathy cohorts determined a prominent role for FLNC in isolated hypertrophic and dilated cardiomyopathies (HCM and DCM). FLNC variants are now among the more prevalent causes of genetic DCM. FLNC-associated DCM is associated with a malignant clinical course and a high risk of sudden cardiac death. The clinical spectrum of FLNC suggests different pathomechanisms related to variant types and their location in the gene. The appropriate functioning of FLNC is crucial for structural integrity and cell signaling of the sarcomere. The secondary protein structure of FLNC is critical to ensure this function. Truncating variants with subsequent haploinsufficiency are associated with DCM and cardiac arrhythmias. Interference with the dimerization and folding of the protein leads to aggregate formation detrimental for muscle function, as found in HCM and MFM. Variants associated with HCM are predominantly missense variants, which cluster in the ROD2 domain. This domain is important for binding to the sarcomere and to ensure appropriate cell signaling. We here review FLNC genotype-phenotype correlations based on available evidence.

Hypertrophic remodelling in cardiac regulatory myosin light chain (MYL2) founder mutation carriers.

AIMS: Phenotypic heterogeneity and incomplete penetrance are common in patients with hypertrophic cardiomyopathy (HCM). We aim to improve the understanding in genotype-phenotype correlations in HCM, particularly the contribution of an MYL2 founder mutation and risk factors to left ventricular hypertrophic remodelling. METHODS AND RESULTS: We analysed 14 HCM families of whom 38 family members share the MYL2 c.64G > A [p.(Glu22Lys)] mutation and a common founder haplotype. In this unique cohort, we investigated factors influencing phenotypic outcome in addition to the primary mutation. The mutation alone showed benign disease manifestation with low penetrance. The co-presence of additional risk factors for hypertrophy such as hypertension, obesity, or other sarcomeric gene mutation increased disease penetrance substantially and caused HCM in 89% of MYL2 mutation carriers (P = 0.0005). The most prominent risk factor was hypertension, observed in 71% of mutation carriers with HCM and an additional risk factor. CONCLUSION: The MYL2 mutation c.64G > A on its own is incapable of triggering clinical HCM in most carriers. However, the presence of an additional risk factor for hypertrophy, particularly hypertension, adds to the development of HCM. Early diagnosis of risk factors is important for early treatment of MYL2 mutation carriers and close monitoring should be guaranteed in this case. Our findings also suggest that the presence of hypertension or another risk factor for hypertrophy should not be an exclusion criterion for genetic studies.

Juvenile-onset multifocal atrial arrhythmias, atrial standstill and compound heterozygosity of genetic variants in TAF1A: sentinel event for evolving dilated cardiomyopathy-a case report.

Background: Juvenile onset of extensive atrial electromechanical failure, including atrial standstill, is a rare disease entity that may precede ventricular cardiomyopathy. Genetic variants associated with early-onset atrioventricular (AV) cardiomyopathy are increasingly recognized. Case summary: A 16-year-old patient presented with atrial brady- and tachyarrhythmias and concomitant impaired atrial electromechanical function (atrial standstill). The atrial phenotype preceded the development of a predominantly right-sided AV dilated cardiomyopathy with pronounced myocardial fibrosis. A His-bundle pacemaker was installed for high-degree AV conduction block and sinus arrest. Using familial-based whole-exome sequencing, a missense mutation and a copy number variant deletion (compound heterozygosity) of the TAF1A gene (involved in ribosomal RNA synthesis) were identified. Discussion: Juvenile onset of severe atrial electromechanical failure with atrial arrhythmias should prompt deep pheno- and genotyping and calls for vigilance for downstream cardiomyopathic deterioration.

Diagnostic and prognostic relevance of using large gene panels in the genetic testing of patients with dilated cardiomyopathy.

It was previously suggested that increasing the number of genes on diagnostic gene panels could increase the genetic yield in patient with dilated cardiomyopathy (DCM). We explored the diagnostic and prognostic relevance of testing DCM patients with an expanded gene panel. The current study included 225 consecutive DCM patients who had no genetic diagnosis after a 48-gene cardiomyopathy-panel. These were then evaluated using an expanded gene panel of 299 cardiac-associated genes. A likely pathogenic/pathogenic (P/LP) variant was detected in 13 patients. Five variants were reclassifications of variants found in genes which were already detected using the 48 gene panel. Only one of the other eight variants could explain the phenotype of the patient (KCNJ2). The panel detected 186 VUSs in 127 patients (of which 6 also had a P/LP variant). The presence of a VUS was significantly associated with the combined end-point of mortality, heart failure hospitalization, heart transplantation or life-threatening arrhythmias(HR, 2.04 [95% CI, 1.15 to 3.65]; p = 0.02). The association of a VUS with prognosis remained when we only included VUSs in robust DCM-associated genes (high suspicious VUSs), but disappeared when we only included VUSs in non-robust DCM-associated genes (low suspicious VUSs), highlighting the importance of weighing of VUSs. Overall, the use of large gene panels for genetic testing in DCM does not increase the diagnostic yield, although a VUS in a robust DCM-associated gene is associated with an adverse prognosis. Altogether, current diagnostic gene panels should be limited to the robust DCM-associated genes.

Prevalence and Clinical Consequences of Multiple Pathogenic Variants in Dilated Cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy (DCM) was considered a monogenetic disease that can be caused by over 60 genes. Evidence suggests that the combination of multiple pathogenic variants leads to greater disease severity and earlier onset. So far, not much is known about the prevalence and disease course of multiple pathogenic variants in patients with DCM. To gain insight into these knowledge gaps, we (1) systematically collected clinical information from a well-characterized DCM cohort and (2) created a mouse model. METHODS: Complete cardiac phenotyping and genotyping was performed in 685 patients with consecutive DCM. Compound heterozygous digenic (LMNA [lamin]/titin deletion A-band) with monogenic (LMNA/wild-type) and wild-type/wild-type mice were created and phenotypically followed over time. RESULTS: One hundred thirty-one likely pathogenic/pathogenic (LP/P) variants in robust DCM-associated genes were found in 685 patients with DCM (19.1%) genotyped for the robust genes. Three of the 131 patients had a second LP/P variant (2.3%). These 3 patients had a comparable disease onset, disease severity, and clinical course to patients with DCM with one LP/P. The LMNA/Titin deletion A-band mice had no functional differences compared with the LMNA/wild-type mice after 40 weeks of follow-up, although RNA-sequencing suggests increased cardiac stress and sarcomere insufficiency in the LMNA/Titin deletion A-band mice. CONCLUSIONS: In this study population, 2.3% of patients with DCM with one LP/P also have a second LP/P in a different gene. Although the second LP/P does not seem to influence the disease course of DCM in patients and mice, the finding of a second LP/P can be of importance to their relatives.

Implications of Genetic Testing in Dilated Cardiomyopathy.

BACKGROUND: Genetic analysis is a first-tier test in dilated cardiomyopathy (DCM). Electrical phenotypes are common in genetic DCM, but their exact contribution to the clinical course and outcome is unknown. We determined the prevalence of pathogenic gene variants in a large unselected DCM population and determined the role of electrical phenotypes in association with outcome. METHODS: This study included 689 patients with DCM from the Maastricht Cardiomyopathy Registry, undergoing genetic evaluation using a 48 cardiomyopathy-associated gene-panel, echocardiography, endomyocardial biopsies, and Holter monitoring. Upon detection of a pathogenic variant in a patient with DCM, familial segregation was performed. Outcome was defined as cardiovascular death, heart transplantation, heart failure hospitalization, and/or occurrence of life-threatening arrhythmias. RESULTS: A (likely) pathogenic gene variant was found in 19% of patients, varying from 36% in familial to 13% in nonfamilial DCM. Family segregation analysis showed familial disease in 46% of patients with DCM who were initially deemed nonfamilial by history. Overall, 18% of patients with a nongenetic risk factor had a pathogenic gene variant. Almost all pathogenic gene variants occurred in just 12 genes previously shown to have robust disease association with DCM. Genetic DCM was independently associated with electrical phenotypes such as atrial fibrillation, nonsustained ventricular tachycardia, and atrioventricular block and inversely correlated with the presence of a left bundle branch block (P<0.01). After a median follow-up of 4 years, event-free survival was reduced in genetic versus patients with nongenetic DCM (P=0.01). This effect on outcome was mediated by the associated electrical phenotypes of genetic DCM (P<0.001). CONCLUSIONS: One in 5 patients with an established nongenetic risk factor or a nonfamilial disease still carries a pathogenic gene variant. Genetic DCM is characterized by a profile of electrical phenotypes (atrial fibrillation, nonsustained ventricular tachycardia, and atrioventricular block), which carries increased risk for adverse outcomes. Based on these findings, we envisage a broader role for genetic testing in DCM.

Mutations in PDLIM5 are rare in dilated cardiomyopathy but are emerging as potential disease modifiers.

BACKGROUND: A causal genetic mutation is found in 40% of families with dilated cardiomyopathy (DCM), leaving a large percentage of families genetically unsolved. This prevents adequate counseling and clear recommendations in these families. We aim to identify novel genes or modifiers associated with DCM. METHODS: We performed computational ranking of human genes based on coexpression with a predefined set of genes known to be associated with DCM, which allowed us to prioritize gene candidates for their likelihood of being involved in DCM. Top candidates will be checked for variants in the available whole-exome sequencing data of 142 DCM patients. RNA was isolated from cardiac biopsies to investigate gene expression. RESULTS: PDLIM5 was classified as the top candidate. An interesting heterozygous variant (189_190delinsGG) was found in a DCM patient with a known pathogenic truncating TTN-variant. The PDLIM5 loss-of-function (LoF) variant affected all cardiac-specific isoforms of PDLIM5 and no LoF variants were detected in the same region in a control cohort of 26,000 individuals. RNA expression of PDLIM5 and its direct interactors (MYOT, LDB3, and MYOZ2) was increased in cardiac tissue of this patient, indicating a possible compensatory mechanism. The PDLIM5 variant cosegregated with the TTN-variant and the phenotype, leading to a high disease penetrance in this family. A second patient was an infant with a homozygous 10 kb-deletion of exon 2 in PDLIM5 resulting in early-onset cardiac disease, showing the importance of PDLIM5 in cardiac function. CONCLUSIONS: Heterozygous PDLIM5 variants are rare and therefore will not have a major contribution in DCM. Although they likely play a role in disease development as this gene plays a major role in contracting cardiomyocytes and homozygous variants lead to early-onset cardiac disease. Other environmental and/or genetic factors are probably necessary to unveil the cardiac phenotype in PDLIM5 mutation carriers.