550
These results suggest that some novel mutations should exist on one of the alleles in some unknown region of the GCH1 gene , and may decrease the GCH1 mRNA causing the HPD / DRD symptoms . .
 HPD, DRD
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease 
Text: {0} 
Answer:
 HPD, DRD