Human plasticity-related genes (PRGs, lipid phosphate phosphatase-related proteins LPPRs) comprise 5 members expressed in the CNS. They are membrane-spanning enzymes thought to mediate the extracellular concentration and signal transduction of lipid phosphate esters such as lysophosphatidic acid (LPA) and spingosine-1 phosphate (S1P) by hydrolysing their phosphate groups. LPPR4 has been shown to act as an ecto-enzyme in axon growth and regenerative sprouting by mediating LPA levels (Brauer et al. 2003). The activity of the other LPPR members has yet to be defined (Strauss & Brauer 2013).