Human Phosphoinositol Kinase Family Genes encode Phosphoinositol Kinases, enzymes that phosphorylate at various positions the inositol group in membrane-bound phosphatidylinositol, often in response to extracellular signals through G-Protein Coupled Receptors or Receptor Tyrosine Kinases. The resultant phosphoinositides act as selective membrane docking sites for signal transduction proteins with diverse PH domains. Phosphorylated inositols are released as second messengers by enzymatic cleavage of the phosphoinositides. [ ]