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To derive an animal model for the Lesch - Nyhan syndrome , we have used cultured mouse embryonic stem cells , mutagenized by retroviral insertion and selected for loss of HPRT activity , to construct chimaeric mice .
 Lesch - Nyhan syndrome
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease 
Text: {0} 
Answer:
 Lesch - Nyhan syndrome