Cardiomyopathy, Dilated ; Cardiomyopathy, Restrictive/genetics* ; Humans ; Mutation ; Pedigree ; Tropomyosin/genetics*

OBJECTIVE: To identify the pathogenesis in two patients of restrictive cardiomyopathy (RCM) using high-throughput sequencing. METHODS: Peripheral blood samples from the two patients and their parents were collected and genomic DNAs were extracted to conduct targeted next generation sequencing or whole exome sequencing. Bioinformation analysis was performed to identify the pathogenic variants in genes associated with cardiomyopathy, which were further validated by Sanger sequencing. RESULTS: By high throughput sequencing, we detected a de novo heterozygous variant c.549+1G>T in TNNI3 gene in patient 1. The variant has not been reported previously and was predicted to be pathogenic in line with American College of Medical Genetics and Genomics (ACMG) guidelines (PVS1+PS2+PM2). Another heterozygous variant c.433C>T (p.Arg145Trp) in TNNI3 gene was identified in patient 2 and his father. The variant had been reported as pathogenic variant in Clinvar and HGMD databases; based on ACMG guidelines, the variant was predicted to be likely pathogenic (PS3+PM1+PP3). CONCLUSION TNNI3 variants may be the causative gene responsible for restrictive cardiomyopathy in the two patients. High throughput sequencing results provide bases for the diagnosis of restrictive cardiomyopathy.
Cardiomyopathy, Restrictive/genetics* ; Child ; Genomics ; Heterozygote ; Humans ; Mutation ; Whole Exome Sequencing

OBJECTIVERestrictive cardiomyopathy (RCM) is rare in children, and little is known about the molecular basis of RCM. The aim of this study was to investigate the clinical and myopathological characteristics and to detect mutations on cardiac sarcomere protein genes in three idiopathic pediatric RCMs.

METHODSDetailed clinical characteristics and familiar history were obtained in three idiopathic pediatric RCMs. One hundred healthy pediatric individuals were recruited as controls. Histological evaluation was performed with heart tissue retrieved at catheterization in case-1 and case-2. The entire coding sequences of four cardiac sarcomere protein genes, including cardiac troponin T (TNNT2), cardiac troponin I(TNNI3), β-myosin heavy chain (MYH7), and α-actin (ACTC)were screened for mutations. Sequence variants were then tested in the family as well as in 100 healthy control DNAs.

RESULTSAll three index cases were diagnosed as primary RCMs without family history, and their clinical conditions deteriorated rapidly. Case-1 was in combination with ventricular septal defect. Case-2 was in combination with mid- and inferoseptal hypertrophy. In case-1, myocardial biopsies displayed extensive an isomorphism and disarray of cardiomyocytes; electron microscopy showed large stacks of severely dysmorphic megamitochondria and focal Z-disc streaming. In case-2, endomyocardial biopsy revealed moderate myocyte hypertrophy with mild interstitial fibrosis; transmission electron microscopy showed misalignment of Z-bands and unequal Z-Z band distances. Genetic analysis identified two heterozygous missense mutations in TNNI3, with R204H in case-1 and R192H in case-3 respectively. A de novo heterozygous deletion in TNNT2 (p. Asn100_Glu101del) was identified in case-2. Sequence analysis shows that all three mutations are located in a position highly conserved across many species. The three mutations were negative for their parents and controls.

CONCLUSIONThe clinical conditions in all three index cases are deteriorated rapidly after diagnosed as primary RCM. Three heterozygous mutations including two in TNNI3 and one in TNNT2 gene are identified in the three RCMs respectively, which are considered as causative mutations. These findings provide new insights into the molecular etiology responsible for pediatric RCM.

Amino Acid Sequence ; Cardiomyopathy, Restrictive ; genetics ; Child ; DNA Mutational Analysis ; Female ; Humans ; Molecular Sequence Data ; Mutation ; Troponin I ; genetics ; Troponin T ; genetics