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Anencephaly has been suggested to develop from exencephaly ; however , there is little direct experimental evidence to support this , and the mechanism of transformation remains unclear .
 Anencephaly, exencephaly
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 Anencephaly, exencephaly