821
The limb defects , oligodactyly and syndactyly , have been traced to improper differentiation of the apical ectodermal ridge ( AER ) and shortening of the anteroposterior limb axis .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
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