5421
In past decades , the blood ( serum or plasma ) BDNF protein levels and BDNF gene alleles and genotypes to the clinical features of schizophrenia , such as age of onset , clinical subtypes , symptom severity , and drug response , have been evaluated among different populations .
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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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