The purpose of the sudy is to conduct a small study to gather the preliminary data for future lage scale clinical studies that will be designed test the potential beneficial effect of over-the counter study anti-oxidant drug called N-acetylcysteine (NAC) in patients with a heart muscle condition called Hypertrophic Cardiomyopathy (HCM). The present study is a pilot feasibility study, the investigators want to find out whether the investigators can recruit and retain patients with HCM in the study and whether these patients can tolerate this drug and can stay on one year. Likewise, the investigators want to find out any potential side effects that this drug might have and estimate whether it has any beneficial effects.

The primary objective is to perform a pilot study in patients with hypertrophic cardiomyopathy (HCM) and mutations in genes encoding sarcomere proteins to assess safety and gather the pre-requisite data for subsequent robust randomized placebo-controlled efficacy studies with N-acetylcysteine (NAC). Data will be gathered on the recruitment, accrual, retention, and compliance rates of HCM patients randomized to treatment with a placebo or two escalating doses of NAC. Likewise, any potential side effects will be determined and the effect size of NAC on indices of cardiac hypertrophy will be estimated. HCM, the main focus of the study team's research during the past two decades, is the most common cause of sudden cardiac death (SCD) in the young and an important cause of morbidity in the elderly. Despite its clinical impact, there is no effective pharmacological therapy for HCM. None of the current pharmacological therapies reverses or attenuates cardiac hypertrophy or reduces the risk of SCD in adults. Cardiac hypertrophy, the quintessential clinical feature of human HCM, is a major determinant of morbidity and the risk of SCD. Regression of cardiac hypertrophy is expected to improve morbidity and decrease the risk of SCD in HCM, as observed upon regression of load-dependent cardiac hypertrophy. The study team has generated transgenic rabbit and mouse models of HCM and shown that cardiac hypertrophy and fibrosis could be reversed through genetic or pharmacological interventions. Results with NAC, a precursor to glutathione, the largest intracellular thiol pool against oxidative stress, were most promising. In three independent studies in two different transgenic models of HCM (rabbits and mouse), treatment with NAC completely reversed cardiac hypertrophy and fibrosis and improved indices of diastolic function. The ultimate goal of every physician-scientist is to apply the bench discoveries at the bedside. The study team proposes to test their findings in the animal models in humans with HCM caused by sarcomere protein mutations. The use of NAC is also supported by data showing increased oxidative stress in human HCM. Moreover, NAC has been used extensively in humans and has a well-established safety profile. Resources including patients with sarcomere protein mutations are available to successfully complete a randomized placebo-controlled (N=25) pilot study to test two escalating doses of NAC (N=50), administered for one year. The study aims to determine recruitment, accrual, retention and compliance rates; tolerability, safety and side effects; and estimate the effect size of NAC on the indices of cardiac hypertrophy at the baseline and after one year of treatment. Only HCM patients with sarcomere proteins mutations will be included to exclude phenocopy. The Core centers will interpret the phenotypic data to assure homogeneity. Data Coordinating Center will assist in the research design, planning and conduct of the study and analysis of the data. The findings will set the stage for large-scale robust randomized placebo-control efficacy studies.

Inclusion Criteria:

• Patients with primary cardiac hypertrophy, non-dilated LV cavity and preserved LV systolic function, hence, the diagnosis of HCM, who have at least an LV end diastolic (LVSD) wall thickness of at least 15 mm on a 2D echocardiogram and
• Known to have mutations in genes encoding sarcomeric proteins

Exclusion Criteria:

• Hypersensitivity to NAC

• Individuals younger than 18 years old (in the pilot study)

• Phenocopy conditions, diagnosed clinically or genetically

• Patients who have undergone transcatheter (alcohol) septal ablation within 6 months.

• Individuals (typically family members) with causal mutations but an LVSD wall thickness of <15 mm

• Patients with concomitant diseases such as:

  • Significant coronary artery disease >70% luminal diameter stenosis in ny of the major coronary arteries (if known);

  • Valvular heart diseases (more than mild aortic stenosis and mitral regurgitation, the latter judged to be due to primary mitral valve abnormalities);

  • Uncontrolled hypertension, defined as systolic blood pressure of

    • 140 mmHg and diastolic blood pressure of ≥90 mmHg on medication, mean of three measurements at rest);

  • Other significant medical problems, such as moderate to severe chronic renal failure (GFR<45 ml/min/1.73m2), advanced liver disease, cancer, or other disabling conditions

• Pregnant women, nursing mothers and those who plan pregnancy during the study period

• Those with active asthma (albeit the concern is relevant to nebulizer form but not oral formulations)

12 months

The small sample size of the study prohibits from making firm conclusions about efficacy of NAC in hypertrophic cardiomyopathy (HCM).