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Missense mutations in the proteolipid protein 1 ( PLP1 ) gene cause a wide spectrum of hypomyelinating disorders , from mild spastic paraplegia type 2 to severe Pelizaeus - Merzbacher disease ( PMD ) .
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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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