The present invention includes crystalline forms of 2-amino-3-methyl-N-(2-morpholinoethyl)-pentanamide disulfate and crystalline forms of 2-amino-3-methyl-N-(2-morpholinoethyl)-pentanamide monosulfate. Furthermore, the present invention provides compositions comprising the crystalline forms and therapeutic use of the crystalline forms. In one embodiment, the crystal-line compound is (2S,3S)-2-amino-3-methyl-N-(2-morpholinoethyl)-pentanamide.