Missing Pieces

Abstract

Familial hypertrophic cardiomyopathy (FHC)-hereditary cardiac hypertrophy in the absence of abnormal load-is arguably the best example of how genetic approaches have substantially augmented our insight into cardiac disease. For decades, it was recognized that hypertrophic cardiomyopathy could segregate in families, but only recently, with the advent of more powerful genetic tools, has it been possible to identify chromosomal loci associated with the disease and even to define specific genes as the causative factors. Linkage mapping has disclosed the existence of at least five loci associated with FHC, on chromosomes 14q11, 15q2, 1q3, 11p13-q13, and 7q3, and the culprit genes have been established for the first four of these: beta-myosin heavy chain (beta-MHC), [1] alpha-tropomyosin, [2] cardiac troponin T, [2] and myosin binding protein C (MyBP-C), [3,4] respectively. Thus, each of the reported FHC disease genes encodes a protein that is localized to the sarcomere of cardiac muscle. The resulting paradigm of FHC as a disease of the sarcomere [2] provides a rational basis for this unifying phenotype to arise from multiple genetic anomalies and fosters the prediction that disease genes yet to be identified will include additional components of the sarcomere or, potentially, regulators of sarcomere function. Of the proteins implicated in FHC to date, MyBP-C is by far the least familiar and least well understood. MyBP-C first was discovered more than 20 years ago as a contaminant associated with myosin preparations and was subsequently shown to belong to the intracellular immunoglobulin super-family, with fiber-specific isoforms. [5] MyBP-C is localized to the A band of sarcomeres (more specifically, to the cross-bridge-bearing C region) and is aligned transversely in a series of periodic stripes, suggesting …