Dilated cardiomyopathy and hypertrophic cardiomyopathy arise from mutations in many genes. TTN, the gene encoding the sarcomere protein titin, has been insufficiently analyzed for cardiomyopathy mutations because of its enormous size. We analyzed TTN in 312 subjects with dilated cardiomyopathy, 231 subjects with hypertrophic cardiomyopathy, and 249 controls by using next-generation or dideoxy sequencing. We evaluated deleterious variants for cosegregation in families and assessed clinical characteristics. We identified 72 unique mutations (25 nonsense, 23 frameshift, 23 splicing, and 1 large tandem insertion) that altered full-length titin. Among subjects studied by means of next-generation sequencing, the frequency of TTN mutations was significantly higher among subjects with dilated cardiomyopathy (54 of 203 [27%]) than among subjects with hypertrophic cardiomyopathy (3 of 231 [1%], P=3×10⁻¹⁶) or controls (7 of 249 [3%], P=9×10⁻¹⁴). TTN mutations cosegregated with dilated cardiomyopathy in families (combined lod score, 11.1) with high (>95%) observed penetrance after the age of 40 years. Mutations associated with dilated cardiomyopathy were overrepresented in the titin A-band but were absent from the Z-disk and M-band regions of titin (P≤0.01 for all comparisons). Overall, the rates of cardiac outcomes were similar in subjects with and those without TTN mutations, but adverse events occurred earlier in male mutation carriers than in female carriers (P=4×10⁻⁵). TTN truncating mutations are a common cause of dilated cardiomyopathy, occurring in approximately 25% of familial cases of idiopathic dilated cardiomyopathy and in 18% of sporadic cases. Incorporation of sequencing approaches that detect TTN truncations into genetic testing for dilated cardiomyopathy should substantially increase test sensitivity, thereby allowing earlier diagnosis and therapeutic intervention for many patients with dilated cardiomyopathy. Defining the functional effects of TTN truncating mutations should improve our understanding of the pathophysiology of dilated cardiomyopathy. (Funded by the Howard Hughes Medical Institute and others.)

Nonischemic dilated cardiomyopathy is a common heart muscle disease with a prevalence of at least 1 in 2500 adults.¹ It is characterized by left ventricular cavity enlargement and impaired contractility in the absence of significant coronary artery disease.¹ The condition is associated with significant morbidity and mortality due to progressive heart failure (HF) and sudden cardiac death (SCD).² Despite therapeutic advances, 5-year mortality remains as high as 20%.² Risk stratification in dilated cardiomyopathy therefore constitutes a crucial part of patient management with implications for surveillance, treatment, and outcome. Currently, risk stratification is heavily dependent on the assessment of left ventricular ejection fraction (LVEF), as exemplified by its use as the key determinant of device implantation.³ Although LVEF is an important prognostic factor in dilated cardiomyopathy,^4,5 effective risk stratification remains challenging, particularly with respect to SCD.^6,7 Most patients who experience SCD do not have severely reduced LVEF, and many patients with significant impairment of LVEF may still be at low risk for SCD.^7,8 Identification of better independent prognostic factors is necessary to enable clinicians to more accurately stratify risk in patients with dilated cardiomyopathy and tailor management accordingly.

The accurate interpretation of variation in Mendelian disease genes has lagged behind data generation as sequencing has become increasingly accessible. Ongoing large sequencing efforts present huge interpretive challenges, but they also provide an invaluable opportunity to characterize the spectrum and importance of rare variation. We analyzed sequence data from 7,855 clinical cardiomyopathy cases and 60,706 Exome Aggregation Consortium (ExAC) reference samples to obtain a better understanding of genetic variation in a representative autosomal dominant disorder. We found that in some genes previously reported as important causes of a given cardiomyopathy, rare variation is not clinically informative because there is an unacceptably high likelihood of false-positive interpretation. By contrast, in other genes, we find that diagnostic laboratories may be overly conservative when assessing variant pathogenicity. We outline improved analytical approaches that evaluate which genes and variant classes are interpretable and propose that these will increase the clinical utility of testing across a range of Mendelian diseases.Genet Med 19 2, 192-203.

Fibroblast-specific Il-11 expression causes heart and kidney fibrosis and organ failure, whereas IL-11 inhibition prevents fibroblast activation and organ fibrosis, indicating that IL-11 inhibition is a potential therapeutic strategy to treat fibrotic diseases. Fibrosis—the overproduction of fibrous connective tissue—is a feature of many diseases and can contribute to pathology by causing scarring, thickening of tissue and interference with normal organ function. In the heart, fibrosis can cause mechanical and electrical dysfunction. Stuart Cook and colleagues identify a protein that has a crucial role in cardiac fibrosis: the cytokine IL-11. They find that, in primary human cardiac fibroblasts, transcription of IL-11 is a dominant response to transforming growth factor beta (TGFβ) exposure and that it is required for the pro-fibrotic effect of TGFβ. Loss of IL-11 reduced fibrosis in three preclinical models of cardiovascular fibrosis, leading the authors to propose IL-11 as a therapeutic target. Fibrosis is a common pathology in cardiovascular disease1. In the heart, fibrosis causes mechanical and electrical dysfunction1,2 and in the kidney, it predicts the onset of renal failure3. Transforming growth factor β1 (TGFβ1) is the principal pro-fibrotic factor4,5, but its inhibition is associated with side effects due to its pleiotropic roles6,7. We hypothesized that downstream effectors of TGFβ1 in fibroblasts could be attractive therapeutic targets and lack upstream toxicity. Here we show, using integrated imaging–genomics analyses of primary human fibroblasts, that upregulation of interleukin-11 (IL-11) is the dominant transcriptional response to TGFβ1 exposure and required for its pro-fibrotic effect. IL-11 and its receptor (IL11RA) are expressed specifically in fibroblasts, in which they drive non-canonical, ERK-dependent autocrine signalling that is required for fibrogenic protein synthesis. In mice, fibroblast-specific Il11 transgene expression or Il-11 injection causes heart and kidney fibrosis and organ failure, whereas genetic deletion of Il11ra1 protects against disease. Therefore, inhibition of IL-11 prevents fibroblast activation across organs and species in response to a range of important pro-fibrotic stimuli. These results reveal a central role of IL-11 in fibrosis and we propose that inhibition of IL-11 is a potential therapeutic strategy to treat fibrotic diseases.

A giant disruption of the heart: Certain forms of heart failure originate from genetic mutations. Understanding how the culprit mutant proteins alter normal heart function could lead to more effective treatments. One candidate is the giant protein tintin, which is mutated in a subset of patients with dilated cardiomyopathy. Through a combination of patient-derived stem cells, tissue engineering, and gene editing, Hinson et al. found that disease-associated titin mutations disrupt the function of the contractile unit in heart muscle. As a result, the heart does not respond properly to mechanical and other forms of stress. Science , this issue p. 982