The word dysplexia has alternate spelling of 'dysplasia' and means pathologically altered cell structure. In case of your son, doctor might be referring to altered neurons of speech area of cerebral cortex.
Boys commonly speak late and you have to wait a while at least till he is three. He must be uttering monosyllables like mama, dada etc. and understanding simple spoken commands and conversation and expressing his needs through gestures. Please act dumb at first and do not fulfill his demand instantly from gestures but make him utter words for that.
Also make him listen to lot of rhymes and songs.