Protein aggregation cardiomyopathy is a life-threatening manifestation of a multisystem disorder caused by the exchange mutation in the gene encoding the human small heat shock protein B-crystallin (hR120GCryAB). Genetic studies in mice have established cardiac hR120GCryAB expression causes increased activity of glucose 6-phosphate dehydrogenase (G6PD) and 'reductive stress' (Rajasekeran et al., Cell. 2007;130(3):401-2). However, the initiating molecular events in the pathogenesis of this novel toxic gain-of-function mechanism remain poorly defined. In an integrated systems approach using gene expression profiling, we identified a 'biosignature' whose features can be validated to predict the onset, rate of progression, and clinical outcome of R120GCryAB cardiomyopathy. At the 3 month disease-related but compensated stage, we demonstrate that transcripts were only upregulated in three distinct pathways: stress response (e.g., Hsp70, Hsp90), glutathione metabolism (Gpx1, Gpx3, glutathione S-transferase), and complement and coagulation cascades in hR120GCryAB transgenic mouse hearts compared with either hCryAB WT transgenic mice or non-transgenic controls. In 6 month old myopathic hearts, ribosomal synthesis and cellular remodeling associated with increased cardiac hypertrophy were additional upregulated pathways. In contrast, the predominant down-regulated pathways were for oxidative phosphorylation, fatty acid metabolism, intermediate metabolism, and energetic balance, supporting their primary pathogenic roles by which G6PD-dependent reductive stress causes cardiac decompensation and overt heart failure in hR120GCryAB cardiomyopathy. This study extends and confirms our previous findings that reductive stress is a causal mechanism for hR120G CryAB cardiomyopathy and demonstrates that alteration in glutathione pathway gene expression is an early biosignature with utility for pre-symptomatic detection.