Restrictive and hypertrophic cardiomyopathies in Noonan syndrome: the overlap syndromes

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.

Myocardial fragmentation associated with disruption of the Z-band in hypertrophic cardiomyopathy in Noonan syndrome

A 13-year-old female with Noonan syndrome had been diagnosed with hypertrophic cardiomyopathy, and she died of heart failure at the age of 25 years. Light microscopic and electron microscopic examination of her biopsied myocardium and autopsy heart showed myocardial fragmentation associated with Z-band disruption as well as myocardial hypertrophy and disarray with interstitial fibrosis. Myocardial fragmentation associated with Z-band disruption may be related to the progression of cardiac dysfunction.

Diagnostic work-up in cardiomyopathies: bridging the gap between clinical phenotypes and final diagnosis. A position statement from the ESC Working Group on Myocardial and Pericardial Diseases

In 2008, The ESC Working Group on Myocardial and Pericardial Diseases proposed an updated classification of cardiomyopathies based on morphological and functional phenotypes and subcategories of familial/genetic and non-familial/non-genetic disease. In this position statement, we propose a framework for the clinical approach to diagnosis in cardiomyopathies based on the recognition of diagnostic 'red flags' that can be used to guide rational selection of specialized tests including genetic analysis. The basic premise is that the adoption of a cardiomyopathy-specific mindset which combines conventional cardiological assessment with non-cardiac and molecular parameters increases diagnostic accuracy and thus improves advice and treatment for patients and families.

Survival implications: hypertrophic cardiomyopathy in Noonan syndrome

OBJECTIVES

To understand relationships and survival implications between structural heart disease and hypertrophic cardiomyopathy in Noonan syndrome (Noonan syndrome-HCM), we reviewed the clinical course of 138 children with Noonan syndrome diagnosed with cardiovascular abnormalities and compared survival with the 30 children with Noonan syndrome-HCM with 120 contemporaneous children with nonsyndromic HCM.

METHODS

Study cohorts represent consecutive cases diagnosed at our institution 1966 through 2006. Outcomes were modeled using multiphase parametric techniques followed by multivariable regression with bagging.

RESULTS

Cardiac abnormalities in Noonan syndrome: Cardiac abnormalities in the 138 Noonan syndrome children included pulmonary valve dysplasia (52%), hypertrophic cardiomyopathy (22%), atrial septal defect (20%), ventricular septal defect (10%), mitral valve dysplasia (6%), coarctation (3%), and Fallot's tetralogy (2%). Need for surgery was high but not different from children with structural defects coexisting with HCM. Overall, late survival in children with Noonan syndrome and cardiac defects was good (91 ± 3% at 15 years), although significantly worse for those with Noonan syndrome-HCM (P < .01). Noonan syndrome-HCM vs. nonsyndromic HCM: In the 30 children with Noonan syndrome-HCM, structural cardiac malformations coexisted in 18 (57%). The incidence of structural cardiac malformations in nonsyndromic HCM was instead 3/120 (2.5%, P < .001). Risk-adjusted late survival was significantly worse for Noonan syndrome-HCM than for nonsyndromic HCM (P= .02).

CONCLUSIONS

Noonan syndrome-HCM frequently coexists with structural cardiac malformations, whereas nonsyndromic HCM does not; their natural histories may therefore be different. Late survival is significantly worse for Noonan syndrome-HCM than nonsyndromic HCM.

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.