Required for normal viability, growth and fertility.
Amine and polyamine biosynthesis; spermine biosynthesis; spermine from spermidine: step 1/1.
Defects in SMS are the cause of Snyder-Robinson syndrome (SRS) [MIM:309583]; 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.
Belongs to the spermidine/spermine synthase family.
Composed of 3 domains: the N-terminal domain has structural similarity to S-adenosylmethionine decarboxylase, the central domain is made up of four beta strands and the C-terminal domain is similar in structure to spermidine synthase. The N- and C-terminal domains are both required for activity.