Genetic linkage of a novel autosomal dominant restrictive cardiomyopathy locus

Cardiomyopathy in Children: Classification and Diagnosis: A Scientific Statement From the American Heart Association

In this scientific statement from the American Heart Association, experts in the field of cardiomyopathy (heart muscle disease) in children address 2 issues: the most current understanding of the causes of cardiomyopathy in children and the optimal approaches to diagnosis cardiomyopathy in children. Cardiomyopathies result in some of the worst pediatric cardiology outcomes; nearly 40% of children who present with symptomatic cardiomyopathy undergo a heart transplantation or die within the first 2 years after diagnosis. The percentage of children with cardiomyopathy who underwent a heart transplantation has not declined over the past 10 years, and cardiomyopathy remains the leading cause of transplantation for children >1 year of age. Studies from the National Heart, Lung, and Blood Institute-funded Pediatric Cardiomyopathy Registry have shown that causes are established in very few children with cardiomyopathy, yet genetic causes are likely to be present in most. The incidence of pediatric cardiomyopathy is ≈1 per 100 000 children. This is comparable to the incidence of such childhood cancers as lymphoma, Wilms tumor, and neuroblastoma. However, the published research and scientific conferences focused on pediatric cardiomyopathy are sparcer than for those cancers. The aim of the statement is to focus on the diagnosis and classification of cardiomyopathy. We anticipate that this report will help shape the future research priorities in this set of diseases to achieve earlier diagnosis, improved clinical outcomes, and better quality of life for these children and their families.

Role of Whole-exome Sequencing in Phenotype Classification and Clinical Treatment of Pediatric Restrictive Cardiomyopathy

Background:

Restrictive cardiomyopathy (RCM) is the least common cardiomyopathy in which the walls are rigid and the heart is restricted from stretching and filling properly. Cardiac troponin I (cTnI) mutation-caused myofibril Ca²⁺ hypersensitivity has been shown to be associated with impaired diastolic function. This study aimed to investigate the linkage between the genotype and clinical therapy of RCM.

Methods:

Five sporadic pediatric RCM patients confirmed by echocardiography were enrolled in this study. Whole-exome sequencing (WES) was performed for the cohort to find out candidate causative gene variants. Sanger sequencing confirmed the WES-identified variants.

Results:

TNNI3 variants were found in all of the five patients. R192H mutation was shared in four patients while R204H mutation was found only in one patient. Structure investigation showed that the C terminus of TNNI3 was flexible and mutation on the C terminus was possible to cause the RCM. Catechins were prescribed for the five patients once genotype was confirmed. Ventricular diastolic function was improved in three patients during the follow-up.

Conclusions:

Our data demonstrated that TNNI3 mutation-induced RCM1 is the most common type of pediatric RCM in this study. In addition, WES is a reliable approach to identify likely pathogenic genes of RCM and might be useful for the guidance of clinical treatment scheme.

Precision medicine approach to genetic cardiomyopathy

Precision medicine aims to achieve improved survival by strategies that recognize the genetic and phenotypic individuality of patients and stratify treatment accordingly. Genetic cardiomyopathies represent an ideal disease group to fully embark on this concept: they are in total frequent diseases with a marked morbidity and mortality and there is ample knowledge about their predisposing genetic factors and associated functional mechanisms. The current review highlights the genetic etiology and gives examples of the diverse treatment strategies that are envisaged in the future.

Titin mutation in familial restrictive cardiomyopathy

BACKGROUND

Familial restrictive cardiomyopathy (RCM) caused by a single gene mutation is the least common of the inherited cardiomyopathies. Only a few RCM-causing mutations have been described. Most mutations causing RCM are located in sarcomere protein genes which also cause hypertrophic cardiomyopathy (HCM). Other genes associated with RCM include the desmin and familial amyloidosis genes. In the present study we describe familial RCM with severe heart failure triggered by a de novo mutation in TTN, encoding the huge muscle filament protein titin.

METHODS AND RESULTS

Family members underwent physical examination, ECG and Doppler echocardiogram studies. The family comprised 6 affected individuals aged 12-35 years. Linkage to candidate loci was performed, followed by gene sequencing. Candidate loci/gene analysis excluded 18 candidate genes but showed segregation with a common haplotype surrounding the TTN locus. Sequence analysis identified a de novo mutation within exon 266 of the TTN gene, resulting in the replacement of tyrosine by cysteine. p.Y7621C affects a highly conserved region in the protein within a fibronectin-3 domain, belonging to the A/I junction region of titin. No other disease-causing mutation was identified in cardiomyopathy genes by whole exome sequencing.

CONCLUSIONS

Our study shows, for the first time, that mutations in TTN can cause restrictive cardiomyopathy. The giant filament titin is considered to be a determinant of a resting tension of the sarcomere and this report provides genetic evidence of its crucial role in diastolic function.

Pediatric restrictive cardiomyopathy associated with a mutation in beta-myosin heavy chain

Most children do not have a known cause of cardiomyopathy which limits the potential for disease-specific therapies. Of the different phenotypic presentations of cardiomyopathy, the restrictive form carries the poorest prognosis and has the lowest rate of identification of etiology. We present the first description of a beta-myosin heavy chain gene mutation in an infant with restrictive cardiomyopathy requiring cardiac transplantation. As demonstrated by three-dimensional protein structure modeling, the missense mutation is in a highly conserved amino acid at the critical binding region for the essential light chain. This case emphasizes that mutations in sarcomeric proteins, which are known to cause hypertrophic cardiomyopathy in adults, may be associated with the development of restrictive physiology in childhood. Identification of the genetic basis of pediatric cardiomyopathy has important implications for management and genetic counseling.