GAMT and movement disorder: Urinary Cr and guanidinoacetate (GAA) were analyzed by gas chromatography–mass spectrometry; they showed low level of Cr associated with a relatively high GAA concentration and low Cr/GAA ratio (0.45) whereas a normal value exceeds 1.3 The diagnosis of mixed movement disorders due to an atypical form of CDS was made after the determination of intermediate GAA methyltransferase (GAMT) activity in lymphoblasts.