The zebrafish runzel (ruz) carries a mutation in the titin gene resulting in muscle degeneration and embryonic lethality. At the onset of the visible phenotype (3-3.5 days post fertilization), RNA expression of the tail and trunk (primarily skeletal muscle) was compared between ruz mutants and wildtype siblings using the Affymetrix Zebrafish Gene Chip. Mutant RNA was matched with RNA of wildtype siblings from the same clutch. 3 separate clutches were used (n=3). RNA was labeled, sheered, and hybridized as in Shephard et al. (Shepard et al., 2005) and the data analyzed as in Choe et al. and Weber et al. (Choe et al., 2005; Weber et al., 2005). Results suggest a novel mechanism of titin muscular dystrophy pathogenesis including upregulation of heat shock proteins.