Noonan's cardiomyopathy: a non-hypertrophic variant

Genotype-Phenotype Associations with Restrictive Cardiomyopathy Induced by Pathogenic Genetic Mutations

Restrictive cardiomyopathy (RCM) is an uncommon cardiac muscle disease characterized by impaired ventricular filling and severe diastolic dysfunction with or without systolic dysfunction. The patients with RCM present poor prognosis and high prevalence of sudden cardiac death, especially in the young. The etiology of RCM may be idiopathic, familial or acquired predispositions from various systemic diseases. The genetic background of familial RCM is often caused by mutations in genes encoding proteins of sarcomeres and a significant minority by mutations in non-sarcomeric proteins and transthyretin proteins. It is important to identify the associations between genotype and phenotype to guide clinical diagnosis and treatment. Here, we have summarized the reported index cases with RCM involving genetic etiology to date and highlighted the most significant phenotype results.

Low-dose dasatinib rescues cardiac function in Noonan syndrome

Noonan syndrome (NS) is a common autosomal dominant disorder that presents with short stature, craniofacial dysmorphism, and cardiac abnormalities. Activating mutations in the PTPN11 gene encoding for the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase-2 (SHP2) causes approximately 50% of NS cases. In contrast, NS with multiple lentigines (NSML) is caused by mutations that inactivate SHP2, but it exhibits some overlapping abnormalities with NS. Protein zero-related (PZR) is a SHP2-binding protein that is hyper-tyrosyl phosphorylated in the hearts of mice from NS and NSML, suggesting that PZR and the tyrosine kinase that catalyzes its phosphorylation represent common targets for these diseases. We show that the tyrosine kinase inhibitor, dasatinib, at doses orders of magnitude lower than that used for its anticancer activities inhibited PZR tyrosyl phosphorylation in the hearts of NS mice. Low-dose dasatinib treatment of NS mice markedly improved cardiomyocyte contractility and functionality. Remarkably, a low dose of dasatinib reversed the expression levels of molecular markers of cardiomyopathy and reduced cardiac fibrosis in NS and NSML mice. These results suggest that PZR/SHP2 signaling is a common target of both NS and NSML and that low-dose dasatinib may represent a unifying therapy for the treatment of PTPN11-related cardiomyopathies.

Suberoylanilide Hydroxamic Acid Restores Estrogen Reduced-cTnI Expression in Neonatal Hearts of Mice

Diastolic cardiac dysfunction can be caused by abnormality in cTnI expression during cardiogenesis. In this study, we investigated the effects of estrogen on the abnormal expression of cTnI in the hearts of neonatal mice and its potential epigenetic mechanisms. We then evaluated suberoylanilide hydroxamic acid (SAHA), a HDAC inhibitor, as a new target treatment of diastolic cardiac dysfunction. Postnatal day 0.5 C57BL/6 mice were injected with estrogen for 1 week, then the hearts of 7-day-old neonatal mice were retrieved for examination. The activities of HDAC and HAT were assayed by colorimetry, and the interaction of cTnI with HDAC5 in mice hearts were examined using chromatin immunoprecipitation assays. The expression of cTnI was tested by quantitative real-time RT-PCR and Western blot. Estrogen treated groups displayed a significantly increased HDAC activity in the hearts of neonatal mice while HAT activity remained unchanged. Additionally, HDAC5 was higher at the cTnI promoter, as compared to the saline treated control groups. The acetylation of histone H3K9ac on cTnI promoter significantly decreased in the hearts of neonatal mice treated with estrogen, and the expression of cTnI at transcriptional and protein levels also decreased. SAHA was shown to increase the acetylation of histone H3K9ac and upregulate the expression of cTnI. The data demonstrated that SAHA can correct cTnI expression abnormality caused by estrogen through inhibiting the binding of HDAC5 to the promoter of cTnI. J. Cell. Biochem. 117: 2377-2384, 2016. © 2016 Wiley Periodicals, Inc.

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.

Genetics of restrictive cardiomyopathy

Restrictive physiology, a severe form of diastolic dysfunction, is characteristically observed in the setting of constrictive pericarditis and myocardial restriction. The latter is commonly due to systemic diseases, some of which are inherited as mendelian traits (eg, hereditary amyloidosis), while others are multifactorial (eg, sarcoidosis). When restrictive physiology occurs as an early and dominant feature of a primary myocardial disorder, it may be termed restrictive cardiomyopathy. In the past decade, clinical and genetic studies have demonstrated that restrictive cardiomyopathy as such is part of the spectrum of sarcomeric disease and frequently coexists with hypertrophic cardiomyopathy in affected families.

Adults with genetic syndromes and cardiovascular abnormalities: clinical history and management

Cardiovascular abnormalities, especially structural congenital heart defects, commonly occur in malformation syndromes and genetic disorders. Individuals with syndromes comprise a significant proportion of those affected with selected congenital heart defects such as complete atrioventricular canal, interrupted arch type B, supravalvar aortic stenosis, and pulmonary stenosis. As these individuals age, they contribute to the growing population of adults with special health care needs. Although most will require longterm cardiology follow-up, primary care providers, geneticists, and other specialists should be aware of (1) the type and frequency of cardiovascular abnormalities, (2) the range of clinical outcomes, and (3) guidelines for prospective management and treatment of potential complications. This article reviews fundamental genetic, cardiac, medical, and reproductive issues associated with common genetic syndromes that are frequently associated with a cardiovascular abnormality. New data are also provided about the cardiac status of adults with a 22q11.2 deletion and with Down syndrome.

Extracardiac medical and neuromuscular implications in restrictive cardiomyopathy

Restrictive cardiomyopathy (RCMP) is characterized by restrictive filling and reduced diastolic volume of either or both ventricles with normal or near-normal systolic function and wall thickness. It may occur idiopathically or as a cardiac manifestation of systemic diseases such as scleroderma, amyloidosis, Churg-Strauss syndrome, cystinosis, sarcoidosis, lymphoma, Gaucher's disease, hemochromatosis, Fabry's disease, pseudoxanthoma elasticum, hypereosinophilic syndrome, carcinoid, Noonan's syndrome, reactive arthritis, or Werner's syndrome and various neuromuscular disorders. Whereas in idiopathic RCMP the therapeutic options are only treatment of cardiac congestion, in cases with an underlying disorder, a causal therapy may be available. Patients with RCMP should be investigated as soon as the cardiac diagnosis is established for extracardiac diseases to detect a possibly treatable cause of RCMP before the disease becomes intractable. These investigations include a diligent clinical history and examination, blood tests, and ophthalmologic, otologic, dermatologic, gastroenterologic, nephrologic, hematologic, and neurologic examinations. If extracardiac examinations do not reveal a plausible cause for RCMP, endomyocardial biopsy is indicated.

The role of somatropin therapy in children with Noonan syndrome

Patients with Noonan syndrome, which is thought to have an incidence of 1 : 1,000 to 1 : 2,500 live births, have variable hypogonadism together with features such as pulmonary valvular stenosis, dysmorphism, deafness, visual problems, cryptorchidism, clotting disorders, and short stature. Noonan syndrome is now known to be associated with mutations in the PTPN11 gene encoding the protein tyrosine phosphatase SHP-2 on chromosome 12 (12q24.1). This discovery will facilitate both knowledge of the true incidence and phenotypic diversity. There are poor genotype-phenotype correlations in Noonan syndrome, and the currently defined gene abnormalities only account for a minority of those identified on a clinical basis. Puberty in patients with Noonan syndrome generally occurs spontaneously but is typically delayed. Mean adult height is 162.5cm (men) and 153cm (women), although standards are based on relatively small samples of largely cross-sectional data and are subject to ascertainment bias. Available evidence suggests that there may be disturbance of the growth hormone/insulin-like growth factor axis in Noonan syndrome and that somatropin (growth hormone therapy) dose-dependently improves vertical growth in the short to medium-term. Final height data from a number of European studies will be available later in 2003. Noonan syndrome patients with echocardiographic features of hypertrophic cardiomyopathy may be at particular risk from somatropin therapy because of its known effects on cardiac muscle mass; these patients have generally been excluded from trials of somatropin. Unbiased evidence for the efficacy and safety of somatropin therapy in Noonan syndrome will come from appropriately controlled studies of sufficiently large numbers of patients defined on such a basis and followed to final height. This is now possible but will require international cooperation. Nevertheless, the clinical relevance of somatropin therapy in Noonan syndrome and other short stature syndromes will be dependent on looking beyond improvement in final height (even if achievable) to psychological and quality of life outcomes.

Diastolic heart failure. Constrictive, restrictive, and pericardial

Clinical heart failure with normal systolic function is suggestive of diastolic dysfunction. This can result from myocardial or pericardial disorders. Myocardial disorders are a broad range of pathologies leading to restrictive physiology. Amyloidosis is a prototype of restrictive cardiomyopathy leading to diastolic dysfunction. Pericardial disorders leading to diastolic heart failure are usually in the form of constrictive physiology. Differentiation between restrictive and constrictive pathologies is often difficult and require careful attention to hemodynamic and Doppler echocardiographic features.

A Case of Noonan’s Syndrome with Numerous Cardiac Abnormalities

OBJECTIVE

To report a case of Noonan's syndrome in a patient with numerous cardiac abnormalities.

METHODS

We present a case report of a patient with Noonan's syndrome, including clinical, laboratory, and radiologic findings, and discuss the characteristic features of this condition.

RESULTS

A 19-year-old male patient had most of the typical clinical findings of Noonan's syndrome-dysmorphic face, short stature, ear abnormalities, cryptorchidism, webbed neck, and high palate. In addition, mitral valve prolapse, secondary mitral insufficiency, left ventricular hypertrophy, and secondary tricuspid insufficiency were diagnosed. Although some cardiac abnormalities have been reported in patients with this syndrome, a case with numerous cardiac abnormalities has not been described previously.

CONCLUSION

Noonan's syndrome is a rare disorder with characteristic clinical features and cardiac abnormalities. Although previously reported cases have described cardiovascular anomalies, on review of the literature we found no other case with numerous cardiac abnormalities.

Dilated cardiomyopathy in Noonan's syndrome

Hypertrophic cardiomyopathy, with myocardial fibre disarray, may occur in 20-25% of cases with Noonan's syndrome. However, dilated cardiomyopathy has not previously been reported. We describe a patient with Noonan's syndrome who presented with typical features of dilated cardiomyopathy with biventricular enlargement and left ventricular ejection fraction of 0.16. Endomyocardial biopsy showed focal interstitial fibrosis and fibre hypertrophy but no disarray. This is the first report in the world literature of an association between Noonan's syndrome and dilated cardiomyopathy. It is possible that this linkage with dilated rather than hypertrophic cardiomyopathy is more common in the Chinese.

Restrictive and hypertrophic cardiomyopathies in Noonan syndrome: the overlap syndromes

A woman with Noonan syndrome had clinical and haemodynamic features of restrictive cardiomyopathy. There was no ventricular hypertrophy on echocardiography but myocardial biopsies showed myocyte hypertrophy without pathological disarray. This case illustrates the overlap of the cardiac phenotypes of Noonan syndrome, restrictive cardiomyopathy, and hypertrophic cardiomyopathy.

Probable right ventricular dysplasia and patent foramen ovale presenting with cyanosis and clubbing in a patient with characteristics of Noonan syndrome

Probable right ventricular dysplasia and a patent foramen ovale resulted in cyanotic heart disease in a patient with some characteristics of Noonan syndrome.