Spermine synthase deficiency resulting in X-linked intellectual disability (Snyder-Robinson syndrome).

Polyamines, small positively charged molecules, are vital for cell proliferation and differentiation. They are found ubiquitously in eukaryotic cells. Additionally, they interact with a wide range of other molecules and some membrane associated receptors. Polyamines, spermidine and spermine, are synthesized by two aminopropyltransferases, spermidine synthase and spermine synthase. Recently, mutations in the latter enzyme have been shown to be responsible for an X-linked intellectual disability condition known as Snyder-Robinson syndrome. Spermine synthase deficiency is thus far the only known polyamine deficiency syndrome in humans.