Figure 2. Light micrographs of sections taken from hearts of an HCM patient (A, B) and an unaffected individual (C). Sections were stained with Masson’s Tricombe (A) and hematoxylin and eosin (B, C) and magnified 200-fold. vidual in order to search all known HCM disease genes for mutations (Table 1). A variety of methods, including single-strand conformation polymorphism, denaturing gradient gel electrophoresis, and denaturing high-pressure liquid chromatography, have been proposed to identify mutations that cause autosomal dominant disease (for a discussion of these various methods, see Dracopoli et al. 2002). The concern with these techniques is that none of them detects all genetic variants with absolute certainty. That is, investigators using each of these methods have demonstrated that some variant sequences cannot be distinguished from normal sequences. High-throughput DNA sequencing detects almost all sequence variants. Unfortunately, the cost of screening large numbers of DNA samples is high both because DNA sample preparation requires expensive reagents and because reading DNA sequence traces is labor-intensive. Nevertheless, we have elected to use high-throughput DNA sequence analyses to search for HCM-causing mutations because of the high mutation detection rate of this method. The extreme genetic heterogeneity of HCM is presumed to occur because affected individuals have a reduced life expectancy, hence over the course of many years such mutations are lost from the population (for review, see Towbin 2000; Watkins 2000; Seidman and Seidman 2001). No strong founder effect has been demonstrated for any known HCM-causing mutation. Rather, instances of de novo mutations arising in affected families have been documented. Poison polypeptides can be encoded by two different types of mutationally altered genes. One class of poison polypeptides are caused by missense mutations that alter only a single nucleotide. To date, mutations in β-cardiac MHC and α-tropomyosin all fall in this category. The other class of poison polypeptides are encoded by mutations that cause protein truncation. Many cardiac MyBP-C and cardiac troponin T mutations are of this type. These mutations frequently alter sequences that control RNA splicing. Because we hypothesize that the number of different mutational alterations that can create poison polypeptides by creating missense peptides is finite, we hypothesize that if we sequence the β-cardiac MHC and α-tropomyosin genes of enough affected individuals we will define the complete set of simple genetic alterations that can generate functional dominant-acting mutationally altered sarcomere proteins. The complete set of mutations in these sarcomere protein genes that can cause HCM may eventually provide clues as to the mechanism by which these mutant proteins cause disease, as well as allow the production of useful diagnostic tools for affected individuals. Most previous searches of HCM-causing mutations have been in patients from tertiary referral centers (for discussion, see Spirito et al. 1997; Maron 2002). These individuals, and often one or more family members, demonstrate clinical symptoms associated with HCM. Here we have attempted to search for HCM-causing mutations among individuals who are either self-referred or referred by local cardiologists and may thus constitute a different population of HCM patients. Because these individuals may have milder disease than individuals who are in tertiary care centers and may have life-threatening clinical features, the distribution of HCM-causing mutations in this population may be different from the …