The Sarcomeric Human Cardiomyopathy Registry (SHaRe) originates from international centers deeply invested in clinical investigation and state of the art management of hypertrophic cardiomyopathy (HCM). Unlike single center studies with relatively small patient cohorts and limited follow-up, the value of SHaRe lies in amassing the scale and diversity of patient experience needed to address fundamental questions regarding the natural history of this complex disease.

Background: Mutations in desmoplakin ( DSP ), the primary force transducer between cardiac desmosomes and intermediate filaments, cause an arrhythmogenic form of cardiomyopathy that has been variably associated with arrhythmogenic right ventricular cardiomyopathy. Clinical correlates of DSP cardiomyopathy have been limited to small case series. Methods: Clinical and genetic data were collected on 107 patients with pathogenic DSP mutations and 81 patients with pathogenic plakophilin 2 ( PKP2 ) mutations as a comparison cohort. A composite outcome of severe ventricular arrhythmia was assessed. Results: DSP and PKP2 cohorts included similar proportions of probands (41% versus 42%) and patients with truncating mutations (98% versus 100%). Left ventricular (LV) predominant cardiomyopathy was exclusively present among patients with DSP (55% versus 0% for PKP2 , P <0.001), whereas right ventricular cardiomyopathy was present in only 14% of patients with DSP versus 40% for PKP2 ( P <0.001). Arrhythmogenic right ventricular cardiomyopathy diagnostic criteria had poor sensitivity for DSP cardiomyopathy. LV late gadolinium enhancement was present in a primarily subepicardial distribution in 40% of patients with DSP (23/57 with magnetic resonance images). LV late gadolinium enhancement occurred with normal LV systolic function in 35% (8/23) of patients with DSP . Episodes of acute myocardial injury (chest pain with troponin elevation and normal coronary angiography) occurred in 15% of patients with DSP and were strongly associated with LV late gadolinium enhancement (90%), even in cases of acute myocardial injury with normal ventricular function (4/5, 80% with late gadolinium enhancement). In 4 DSP cases with 18F-fluorodeoxyglucose positron emission tomography scans, acute LV myocardial injury was associated with myocardial inflammation misdiagnosed initially as cardiac sarcoidosis or myocarditis. Left ventricle ejection fraction <55% was strongly associated with severe ventricular arrhythmias for DSP cases ( P <0.001, sensitivity 85%, specificity 53%). Right ventricular ejection fraction <45% was associated with severe arrhythmias for PKP2 cases ( P <0.001) but was poorly associated for DSP cases ( P =0.8). Frequent premature ventricular contractions were common among patients with severe arrhythmias for both DSP (80%) and PKP2 (91%) groups ( P =non-significant). Conclusions: DSP cardiomyopathy is a distinct form of arrhythmogenic cardiomyopathy characterized by episodic myocardial injury, left ventricular fibrosis that precedes systolic dysfunction, and a high incidence of ventricular arrhythmias. A genotype-specific approach for diagnosis and risk stratification should be used.

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Background Heterozygous mutations in sarcomere genes in hypertrophic cardiomyopathy (HCM) are proposed to exert their effect through gain-of-function for missense mutations or loss-of-function for truncating mutations. However, allelic expression from individual mutations has not been sufficiently characterized to support this exclusive distinction in human HCM. Methods and Results Sarcomere transcript and protein levels were analyzed in septal myectomy and transplant specimens from 46 genotyped HCM patients with or without sarcomere gene mutations and 10 control hearts. For truncating mutations in MYBPC3, the average ratio of mutant:wild-type transcripts was ~1:5, in contrast to ~1:1 for all sarcomere missense mutations, confirming that nonsense transcripts are uniquely unstable. However, total MYBPC3 mRNA was significantly increased by ~9 fold in HCM samples with MYBPC3 mutations compared to control hearts and to HCM samples without sarcomere gene mutations. Full-length MYBPC3 protein content was not different between MYBPC3 mutant HCM and control samples and no truncated proteins were detected. By absolute quantification of abundance (AQUA) with multiple reaction monitoring, stoichiometric ratios of mutant sarcomere proteins relative to wild-type were strikingly variable in a mutation-specific manner, with the fraction of mutant protein ranging from 30–84%. Conclusions These results challenge the concept that haploinsufficiency is a unifying mechanism for HCM caused by MYBPC3 truncating mutations. The range of allelic imbalance for several missense sarcomere mutations suggests that certain mutant proteins may be more or less stable, or incorporate more or less efficiently into the sarcomere than wild-type proteins. These mutation-specific properties may distinctly influence disease phenotypes.