SMS (Spermine synthase) belongs to the spermidine/spermine synthase family. It is an enzyme that converts spermidine into spermine. This enzyme is required for normal viability, growth and fertility involved in polyamine metabolism. Defects in SMS are the cause of Snyder-Robinson syndrome (SRS), also known as X-linked mental retardation Snyder-Robinson type. SRS is characterized by moderate intellectual deficit, hypotonia, an unsteady gait, osteoporosis, kyphoscoliosis and facial asymmetry. Transmission is X-linked recessive. Recombinant human SMS protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.