A bone targeted alkaline phosphatase comprising a polypeptide having the structure : Z-sALP-Y-spacer-X-Wn-V, wherein sALP is the extracellular domain of the alkaline phosphatase； wherein V is absent or is an amino acid sequence of at least one amino acid； X is absent or is an amino acid sequence of at least one amino acid； Y is absent or is an amino acid sequence of at least one amino acid； Z is absent or is an amino acid sequence of at least one amino acid； and Wn is a polyaspartate or a polyglutamate wherein n = 10 to 16. Kits and methods of use thereof.
