Spermine synthase（SMS) is amember of the spermidine/spermine synthase family. SMS is an enzyme which converts spermidine into spermine. The SMS enzyme is essential for normal viability， growth and fertility involved in polyamine metabolism. Defects in the SMS gene are the cause of Snyder-Robinson syndrome（SRS)， also known as X-linked mental retardation Snyder-Robinson type. SRS is categorized by moderate intellectual deficit， hypotonia， an unsteady gait， osteoporosis， kyphoscoliosis and facial asymmetry， its transmission is X-linked recessive.
