17190
In addition , further investigation of XLRP carriers may yield insight into how cone structures change over time and ultimately enable understanding of the role of RPGR and RP2 in cone cell survival . European Journal of Human Genetics advance online publication , 27 February 2013 ; doi : 10 . 1038 / ejhg . 2013 . 21 .
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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:
 None