The addition of a third phosphate to obtain PtdIns(4,5)P2 can be performed by two enzymes, which either add the phosphate at the D4 or D5 position in the inositol ring. This last phosphorylation step is depending on where the second phosphphate is located (D5 or D4 repectively). Rephrased from [PMID: 9367159]: "The type I enzyme PIP-4-kinase phosphorylates PtdIns-4-P at the D-5 position (of the inositol ring).The type II enzyme however ( abundant in some tissues), phosphorylates PtdIns-5-P at the D-4 position, and thus should be considered as a 4-OH kinase, or PIP(4)K."