Identification of Novel Mutations in RBM20 in Patients with Dilated Cardiomyopathy

Abstract

IntroductionDilated cardiomyopathy (DCM; OMIM 115200) is a debilitating primary cardiac muscle disease with a 5-year mortality approaching 50% following diagnosis.1,2 Whether familial or sporadic, DCM shows remarkably high genetic heterogeneity. 3,4 To date, the molecular basis of most of DCM cases remains unknown despite the fact that mutations in more than 30 genes have been shown to be disease causing or disease associated. 5,6 Because of this marked locus heterogeneity, the fraction of DCM patients who have a mutation in any one gene is small, and ranged from 0.3% to 5.9% in our recent resequencing studies. [7][8][9][10] Most of the genes with mutations causing DCM encode for sarcomeric proteins involved in contraction, or cytoskeletal proteins important for cell structure or force transduction. 5,6 Exceptions to this include a mutation identifi ed in the eye absent transcription factor 4 (EYA4) in a family with both DCM and sensorineural hearing loss, 11 and mutations in the genes encoding presenilin 1 and 2 ( PSEN1 and PSEN2 ) that we recently identifi ed in DCM families.10 Although the pathogenic mechanisms of EYA4 and the presenilins in DCM remain to be defi ned, both are known to play regulatory roles in the heart even though they are neither essential structural components nor contractile proteins.A recent genetic linkage and gene-mapping study demonstrated that mutations in RBM20 , a ribonucleic acid (RNA)-binding protein gene, cause DCM.12 Th is discovery is intriguing in several aspects. To our knowledge, this is the fi rst report to suggest that a genetic abnormality of an RNA-binding protein can lead to cardiomyopathy.13 It is also noteworthy that RBM20 mutations were associated with severe cases of DCM with high mortality and patients needing heart transplantation. Moreover, the fi ve mutations identifi ed in the fi rst report were concentrated in a small region of RBM20, spanning only fi ve amino acids, and encoded by a single exon. 12To further evaluate the role of RBM20 in DCM pathogenesis and the DCM clinical characteristics caused by RBM20 mutations, we genetically screened a cohort of 312 DCM probands, and their family members when a mutation was identifi ed. We found six unique mutations in six unrelated probands, four of which were novel. Th ese results expand the RBM20 mutation spectrum in DCM and further emphasize the importance of RBM20 in the myocardial disease. Materials and Methods Clinical evaluationWritten, informed consent was obtained from all subjects, and the Institutional Review Boards at the Oregon Health & Science University and the University of Miami approved the study. Th e investigation included 312 probands (290 Caucasians, of whom 7 were of Hispanic descent; 16 African-Americans, 3 Asians and 3 Native Americans/Alaskan Natives) and used methods of clinical categorization of DCM as previously described.14 Clinical data were obtained through our own evaluations, which included minimally a history and physical examination, an electrocardiogram (ECG) and an echocardiogram...

RNA Splicing

“…To date, only mutations in the splicing factor RNA-binding motif protein 20 (RBM20) have been causally linked to heart disease. [76][77][78] The lack of splicing factors in the list of heart disease-causing genes could have multiple explanations. It could be that mutations in splicing factors are severe and embryonically lethal.…”

“…Ever since, mutations in RBM20 have been found in multiple cohorts, being responsible for 3% to 5% of all familial DCM cases. 77,78 Subsequently, a molecular mechanism that links RBM20 to alternative splicing of several pivotal cardiac genes including titin was identified by Guo et al 80 Rbm20-deficient rats with a cardiac phenotype that closely resembles the DCM in individuals with RBM20 mutations were analyzed. RNA sequencing of hearts of the Rbm20-deficient rat and a human RBM20 mutation carrier revealed a set of 30 RBM20-dependent alternatively spliced genes that were conserved between rat and human.…”

Decoding Abnormal Splicing Code in Human Diseases

“…67,68 Recently, mutations in RBM20 gene have been shown to be associated with human dilated cardiomyopathy (DCM). 69,70 Deep sequencing of the cardiac transcriptome revealed aberrant splicing of the titin gene (TTN). 71 The detected aberrant TTN transcript was previously identified to be due to a loss-of-function mutation in RBM20 gene.…”

“…71 The detected aberrant TTN transcript was previously identified to be due to a loss-of-function mutation in RBM20 gene. 69,70 Subsequent analysis revealed actual ciselements on TTN that are recognized by the splicing-suppressive RBM20. 72 Transcriptome-wide RBM20-binding sites in heart were recently reported using photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) followed by highthroughput sequencing of RNA.…”

Dilated Cardiomyopathy

“…2 Discoveries made over the past 20 years have revealed a genetic basis in both inherited and hitherto idiopathic forms, with many different genes implicated. [3][4][5][6][7][8] These developments have enlightened both clinical diagnosis and investigation, and fostered informed therapeutic decisions.…”