The Collaborative International Dictionary of English v.0.48:

Predisponent \Pre`dis*po"nent\, a.
   Disposing beforehand; predisposing. -- n. That which
   predisposes.
   [1913 Webster]

   Predisponent causes. (Med.) See Predisposing causes,
      under Predispose. --Dunglison.
      [1913 Webster]