This paper presents an approach to provide of lexical adaptation in Automatic Speech Recognition (ASR) of the disordered speech from a group of young impaired speakers. The outcome of an Acoustic Phonetic Decoder (APD) is used to learn new lexical variants of the 57-word vocabulary and add them to a lexicon personalized to each user. The possibilities of combination of this lexical adaptation with acoustic adaptation achieved through traditional Maximum A Posteriori (MAP) approaches are further explored, and the results show the importance of matching the lexicon in the ASR decoding phase to the lexicon used for the acoustic adaptation.