What causes fetishes? Are they sexual disorders?
Having one or more fetishes is very widespread, and thus rather normal.


  The prevalence of fetishism is not known with certainty.[21] The
  majority of fetishists are male.[21] In a 2011 study, 30% of men
  reported fetishistic fantasies, and 24.5% had engaged in fetishistic
  acts. Of those reporting fantasies, 45% said the fetish was intensely
  sexually arousing.[23] In a 2014 study, 26.3% of women and 27.8% of
  men acknowledged any fantasies about "having sex with a fetish or
  non-sexual object".
  https://en.wikipedia.org/wiki/Sexual_fetishism


A disorder is per definiton something abnormal


  disorder [dis-or´der] a derangement or abnormality of function;
  http://medical-dictionary.thefreedictionary.com/disorder


So the answer to your question would per definition be: No. Having fetishes is normal and not a disorder.