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Fourth , the disease phenotype is significantly more severe and had an early age of onset ( 16 years ) in a subject homozygous for the expanded allele , which contrasts with Huntington disease and suggests that the expanded allele in the MJD1 gene could exert its effect either by a dominant negative effect ( putatively excluded in HD ) or by a gain of function effect as proposed for HD .
 Huntington disease, HD, HD
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease 
Text: {0} 
Answer:
 Huntington disease, HD, HD