Source : Webster's Revised Unabridged Dictionary (1913)

Agraphia \A*graph"i*a\, n. [Gr. 'a priv. + ? to write.]
   The absence or loss of the power of expressing ideas by
   written signs. It is one form of aphasia.

Source : WordNet®

agraphia
     n : a loss of the ability to write or to express thoughts in
         writing because of a brain lesion [syn: {anorthography},
         {logagraphia}]