Left Ventricular Myocardial Densification Incomplete Type Of Cardiomyopathy Molecular Genetic Mechanisms

RationalLVNC is a rare primary genetic heart disease, characterized by numerous prominent trabeculars and deep intertrabecular recesses in left ventricular. It was previously termed "spongy myocardium" although this term has been abandoned because it underscores the hypothesis that the basic morphogenetic abnormality may be arrest of normal compaction of the loose interwoven mesh of myocardial fibers in the embryo. LVNC may be an isolated finding in the absence of any coexisting cardiac anomaly, called isolated ventricular noncompaction (IVNM),or may be associated with other congenital anomalies, such as Ebstein malformation, ventricular septal defect etc. It is widely accepted that LVNC is caused by noncompaction of the myocardium during embryonic development. The genetic basis of this cardiomyopathy is still largely unsolved and mechanism of the disease remains unclear. The heterogenetiy of the clinical features includes both asymptomatic and symptomatic patients with progressive deterioration in cardiac function that results in congestive heart failure, arrhythmias, thromboembolic events, and sudden cardiac death.Clinical study suggested that LVNC is often familiar with predominantly autosomal domiant inheritance. X-linked recessive inheritance and mitochondrion inheritance of neonatal LVNC also have been described. It has been linked to mutations in genes including sarcomere component (MYH7, ACTC, MYBPC3, TNNT2), cytoskeletal protein (ZASP, LMNA) and TAZ (G4.5). However, mutants in all of the above mentioned genes account for only a small percentage of patients. And mutations in the genes encoding sarcomere proteins have been associated with both hypertrophic and dilated cardiomyopathy. In addition, LVNC happened with neuromuscular diseases such as Barth syndrome. G4.5is a candidate gene for Barth syndrome, encoding a metabolism related phosphatide protein which is located in mitochondria. Based on all of these preceding works, we hypothesized that the pathology of LVNC maybe associated with mitochondria or/and abnormalities in development of myocardiocytes. Thus, expanding the scope of candidate gene scanning, even from the whole genome level, may be an effective way to uncover the pathogeny of LVNC.Aims The present study was undertaken to investigate the molecular genetic basis of LVNC by using technologies of molecular biology, molecular genetics, and high throughput sequencing.Methods and Results1) Pedigree counseling and histopathology investigationPathologic study of LVNC patients’ myocardium reaveled that, myofilament in some patients’myocardium were loosely arranged and severe fibrosis existed between myocardium. However, no common characteristic of pathology was found. Apoptosis exists in all of the four myocardium samples with some myocardium differentiation possitive; No proliferation of myocardium was found. Results from transmission electron microscope showed that, left ventricular myocardial tissue sarcomere was dissolved, and the structure and location of mitochondria was abnormal.2) The investigation to mitochondrial DNA from6LVNC patientsThe patients’ mitochondrial genomic DNA (mtDNA) of LVNC were extracted and sequenced.227abnormal variations were found, among which157variations localized in coding region and70variants localized in non-coding region. Mutant conservative index of m.9856T>C in MT-CO3localized in MT-CO3was high, however, it was excluded from candidated disease-causing gene after pedigree analysis; Results from long segment PCR amplification technology showed that, mtDNA in LVNC myocardium was3840±226.5, lowered than that of normal myocardium (8266±900.8, P<0.01).3) Whole exome sequencingWhole exome sequencing was performed by high-throughput sequencing technologies in four patients with typical LVNC (IVNC). Bioinformatics analysis combined with clinical data and pathologic study reaveled that, abnomalities in Wnt signaling pathway may be one of the causes of LVNC.ConclusionsAlthough there was no consistent pathological characteristics in six LVNC myocardium specimens, muscle fiber disorders and abnormal mitochondria ultrastructure observed by transmission electron microscope suggested that mitochondria dysfunction; Whole exome sequencing analysis revealed that, LVNC may be associated with abnormalities of cell signaling pathway during embryonic heart development. More information might have been found if the patient number were larger and further function studies of mutation genes are needed to reveal the true etiology of LVNC.