Abstract: Objective　To investigate the role of TNSALP gene detection in prenatal diagnosis of HPP. Method　The clinical data and the results of complete exon sequencing of TNSALP gene  in one neonate with low alkaline phosphatase (HPP) were analyzed retrospectively. Peripheral bloods from his family members were collected. The amniotic fluid cell in fetuses at 17 weeks was tested for candidate gene mutations by Sanger sequencing. Results　Mainly manifestations in 6-day-old baby were multiple fractures, limb shortening and bending and dyspnea. He died of respiratory failure 9 days after birth. The serum alkaline phosphatase was decreased and serum calcium was decreased slightly; serum phosphorus, serum 25 hydroxyvitamin-D and parathyroid hormone were normal. X-ray showed that the whole body bone was very poorly mineralized, and the long diaphysis was enlarged with shape of a cup at the end and multiple fractures existed. Gene sequencing revealed a complex heterozygous missense mutation in the TNSALP gene, including the heterozygous missense mutation c.542C>T in exon sixth causing 181st amino acids changed from serine to leucine (p.S181L), and tenth exon heterozygous missense mutation in c.1016G>A causing 339th amino acid changed from glycine to glutamic acid (p.G339E). The parental phenotypes were normal. The c.542C>T mutation is inherited from his father and the c.1016G>A mutation is inherited from his mother. These two mutations were not detected in the fetus. Conclusion　TNSALP gene analysis can be applied to the diagnosis and prenatal diagnosis of HPP.