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Since mdx mice do not develop dystrophic cardiomyopathy until >= 21 months of age , we reasoned that old mdx mice may represent a better model to assess the impact of skeletal muscle rescue on dystrophic heart disease .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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