Mutations in the muscle LIM protein and (alpha)-actinin-2 genes in dilated cardiomyopathy and endocardial fibroelastosis

Dilated cardiomyopathy (DCM) is a major cause of morbidity and mortality. Two genes have been identified for the X-linked forms (dystrophin and tafazzin), while mutations in multiple genes cause autosomal dominant DCM. Muscle LIM protein (MLP) is a member of the cysteinerich protein (CRP) family and has been implicated in both myogenesis and sarcomere assembly. In the latter role, it binds zyxin and (alpha)-actinin, both of which are involved in actin organization. An MLP-deficient mouse has been described; these mice develop dilated cardiomyopathy and heart failure. Based upon these data, and the recent descriptions of mutations in MLP in patients with DCM or hypertrophic cardiomyopathy, we screened patients for mutations in the MLP and (alpha)actinin-2 genes. We identified a patient with DCM and EFE, having a mutation in MLP with the residue lysine 69 substituted by arginine (K69R). This is within a highly conserved region adjacent to the first LIM domain involved in (alpha)-actinin binding. Analysis in cell culture systems demonstrated that the mutation abolishes the interaction between MLP and (alpha)-actinin-2 and the cellular localization of MLP was altered. In another individual with DCM, a W4R mutation was identified. However, this mutation did not segregate with disease in this family. In another patient with DCM, a Q9R mutation was identified in (alpha)-actinin-2. This mutation also disrupted the interaction with MLP and appeared to inhibit (alpha)-actinin function in cultured cells, in respect to the nuclear localization of actinin and the initiation of cellular differentiation.