The genetic basis of pediatric cardiovascular disease

A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model

D-2-hydroxyglutaric aciduria (D2HGA) type II is a rare neurometabolic disorder caused by germline gain-of-function mutations in isocitrate dehydrogenase 2 (IDH2), resulting in accumulation of D-2-hydroxyglutarate (D2HG). Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span. Currently, there are no effective therapeutic interventions. We generated a D2HGA type II mouse model by introducing the Idh2R140Q mutation at the native chromosomal locus. Idh2R140Q mice displayed significantly elevated 2HG levels and recapitulated multiple defects seen in patients. AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function. We observed differential expression of multiple genes and metabolites that are associated with cardiomyopathy, which were largely reversed by AGI-026. These findings demonstrate the potential therapeutic benefit of an IDH2R140Q inhibitor in patients with D2HGA type II.

D-2-hydroxyglutarate produced by mutant IDH2 causes cardiomyopathy and neurodegeneration in mice

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) have been discovered in several cancers, and these mutant enzymes exhibit neomorphic activity resulting in production of D2-hydroxyglutaric acid (D-2HG). Akbay et al. find that adult transgenic mice with conditionally activated IDH2^R140Q and IDH2^R172K alleles exhibit dilated cardiomyopathy and muscular dystrophy. These phenotypes were even more pronounced in embryos. Cardiac hypertrophy was also observed in nude mice implanted with IDH2^R140Q-expressing xenografts. Silencing of IDH2^R140Q in mice with an inducible transgene restored heart function by lowering 2HG levels.

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) have been discovered in several cancer types and cause the neurometabolic syndrome D2-hydroxyglutaric aciduria (D2HGA). The mutant enzymes exhibit neomorphic activity resulting in production of D2-hydroxyglutaric acid (D-2HG). To study the pathophysiological consequences of the accumulation of D-2HG, we generated transgenic mice with conditionally activated IDH2^R140Q and IDH2^R172K alleles. Global induction of mutant IDH2 expression in adults resulted in dilated cardiomyopathy, white matter abnormalities throughout the central nervous system (CNS), and muscular dystrophy. Embryonic activation of mutant IDH2 resulted in more pronounced phenotypes, including runting, hydrocephalus, and shortened life span, recapitulating the abnormalities observed in D2HGA patients. The diseased hearts exhibited mitochondrial damage and glycogen accumulation with a concordant up-regulation of genes involved in glycogen biosynthesis. Notably, mild cardiac hypertrophy was also observed in nude mice implanted with IDH2^R140Q-expressing xenografts, suggesting that 2HG may potentially act in a paracrine fashion. Finally, we show that silencing of IDH2^R140Q in mice with an inducible transgene restores heart function by lowering 2HG levels. Together, these findings indicate that inhibitors of mutant IDH2 may be beneficial in the treatment of D2HGA and suggest that 2HG produced by IDH mutant tumors has the potential to provoke a paraneoplastic condition.

Rapamycin reverses hypertrophic cardiomyopathy in a mouse model of LEOPARD syndrome-associated PTPN11 mutation

LEOPARD syndrome (LS) is an autosomal dominant "RASopathy" that manifests with congenital heart disease. Nearly all cases of LS are caused by catalytically inactivating mutations in the protein tyrosine phosphatase (PTP), non-receptor type 11 (PTPN11) gene that encodes the SH2 domain-containing PTP-2 (SHP2). RASopathies typically affect components of the RAS/MAPK pathway, yet it remains unclear how PTPN11 mutations alter cellular signaling to produce LS phenotypes. We therefore generated knockin mice harboring the Ptpn11 mutation Y279C, one of the most common LS alleles. Ptpn11(Y279C/+) (LS/+) mice recapitulated the human disorder, with short stature, craniofacial dysmorphia, and morphologic, histologic, echocardiographic, and molecular evidence of hypertrophic cardiomyopathy (HCM). Heart and/or cardiomyocyte lysates from LS/+ mice showed enhanced binding of Shp2 to Irs1, decreased Shp2 catalytic activity, and abrogated agonist-evoked Erk/Mapk signaling. LS/+ mice also exhibited increased basal and agonist-induced Akt and mTor activity. The cardiac defects in LS/+ mice were completely reversed by treatment with rapamycin, an inhibitor of mTOR. Our results demonstrate that LS mutations have dominant-negative effects in vivo, identify enhanced mTOR activity as critical for causing LS-associated HCM, and suggest that TOR inhibitors be considered for treatment of HCM in LS patients.

Chromosome 22q11 deletions in patients with conotruncal heart defects

We performed this study to determine the frequency of 22q11 deletions and associated phenotypic features and abnormalities in conotruncal heart defects. Sixty-one patients with conotruncal heart defects, including tetralogy of Fallot (TOF; n = 32), pulmonary atresia/ventricular septal defect (PAVSD; n = 12), double-outlet right ventricle (DORV; n = 5), transposition of the great arteries (TGA; n = 4 ), truncus arteriosus (TA; n = 4), subpulmonary ventricular septal defect (SPVSD; n = 3), and interrupted aortic arch (IAA; n = 1), were enrolled in this study and screened for 22q11 deletions by the fluorescence in situ hybridization technique. Phenotypic features and associated abnormalities, including submucosal cleft palate, abnormal facies, square nose, nasal voice, abnormal ears, long and slender fingers, delayed development, mental retardation, delayed growth, short stature, and hypocalcemia, were examined in these patients. Nine of 61 patients (14.8%) had 22q11 deletions, including 100% of IAA, 50% of TA, 33.3% of SPVSD, 33.3% of PAVSD, and 3.1% of TOF. Deletions were not detected in DORV and TGA. In all patients with 22q11 deletions, > or =1 phenotypic features or associated abnormalities were observed. A subgroup of patients with IAA, TA, SPVSD, and PAVSD associated with phenotypic features or abnormalities warrants evaluation for the presence of 22q11 deletions.

Identification and validation of selective upregulation of ventricular myosin light chain type 2 mRNA in idiopathic dilated cardiomyopathy

BACKGROUND AND AIMS

the etiology of idiopathic dilated cardiomyopathy (IDCM) is unknown, methods such as suppression subtractive hybridization (SSH) and DNA microarray technology can help to identify genes which might be involved in the pathogenesis of this disease.

METHODS AND RESULTS

we used SSH which compared mRNA populations extracted from the left ventricular tissue of IDCM hearts and from the control tissue to identify sequences which correspond to genes up-regulated in IDCM. We identified ventricular myosin light chain type 2 (MLC2V), skeletal alpha-actin, long-chain-acyl-CoA-synthetase and mRNA for the protein KIAA0465 as differentially up-regulated genes. Expression of MLC2V mRNA was determined by RT-PCR in patients with end-stage heart failure caused by IDCM (n=11) or coronary artery disease (CAD, n=9) who underwent heart transplantation as well as the controls (n=6). MLC2V/GAPDH ratios were 2.95+/-0.32, 0.69+/-0.03 and 0.28+/-0.08 (arbitrary unit) for the IDCM group, the CAD group and controls, respectively (P<0.05). DNA microarray analysis confirmed the finding of MLC2V upregulation in IDCM (3.7- and 1.8-fold increase in MLC2V mRNA).

CONCLUSIONS

we have demonstrated that SSH is a useful method to identify differential myocardial upregulation of genes. Upregulation of MLC2V can be judged as a specific IDCM related feature, which might be clinically helpful.

Metabolic cardiomyopathies

The energy needed by cardiac muscle to maintain proper function is supplied by adenosine Ariphosphate primarily (ATP) production through breakdown of fatty acids. Metabolic cardiomyopathies can be caused by disturbances in metabolism, for example diabetes mellitus, hypertrophy and heart failure or alcoholic cardiomyopathy. Deficiency in enzymes of the mitochondrial beta-oxidation show a varying degree of cardiac manifestation. Aberrations of mitochondrial DNA lead to a wide variety of cardiac disorders, without any obvious correlation between genotype and phenotype. A completely different pathogenetic model comprises cardiac manifestation of systemic metabolic diseases caused by deficiencies of various enzymes in a variety of metabolic pathways. Examples of these disorders are glycogen storage diseases (e.g. glycogenosis type II and III), lysosomal storage diseases (e.g. Niemann-Pick disease, Gaucher disease, I-cell disease, various types of mucopolysaccharidoses, GM1 gangliosidosis, galactosialidosis, carbohydrate-deficient glycoprotein syndromes and Sandhoff's disease). There are some systemic diseases which can also affect the heart, for example triosephosphate isomerase deficiency, hereditary haemochromatosis, CD 36 defect or propionic acidaemia.

Radiographic evaluation of the neonate with congenital heart disease

Remarkable advances in pediatric cardiology have been spurred by the explosion of technologies both in interventional and surgical techniques and the ability to manipulate the genome of experimental animals. After a brief discussion concerning the striking advances in the molecular understanding of congenital heart disease, this article focuses on clues to the diagnosis of congenital heart disease and on chest radiography and common, specific lesions of the neonate such as hypoplastic left heart, transposition of the great vessels, and severe tetralogy of Fallot. The impact of treatment protocols involving interventional cardiology in the neonate also are discussed.

Mechanisms of brain injury during infant cardiac surgery

Neurological injury is a major and often debilitating complication of congenital heart disease and open-heart surgery. Paradoxically, the full impact of this complication has been underscored by the marked decrease in mortality and the rescue of infants with desperate and previously lethal heart conditions. Although recent focus has been on mechanisms of brain injury originating during open-heart surgery, this article also emphasizes the importance of mechanisms initiated or perpetuated during the preoperative and postoperative periods. In addition to the usually implicated mechanism of hypoxia-ischemia, recent genetic advances suggest an important role for genetic deletion syndromes. Inflammatory cascades have been implicated in the end-organ injury seen after cardiopulmonary bypass and might play a role in neurological dysfunction. These mechanisms are reviewed, with an emphasis on recent developments in our understanding of brain injury in this population.