In 2015, asfotase alfa (recombinant TNSALP) was approved in the US for perinatal-, infantile-, and juvenile-onset disease, and in 2016 it was approved in the UK for only perinatal- and infantile-onset disease with a cost cap.
 Nonstandard abbreviations: ALP, alkaline phosphatase; PLP, pyridoxal 5'-phosphate; PA, pyridoxic acid; HPP, hypophosphatasia; TNSALP, tissue-nonspecific isoenzyme of alkaline phosphatase; PPi, inorganic pyrophosphate.
Enzyme replacement therapy can be achieved by administration of asfotase alfa, a fusion of the tissue-nonspecific alkaline phosphatase (TNSALP) enzyme to Fc domains that is targeted to bone by a polyaspartic acid tail.
In addition to describing the clinical, radiographic, and biochemical features of this case, we will also report the short-term outcomes of treatment with modified human TNSALP protein.
Two heterozygous, missense mutations in the TNSALP gene were identified that have previously been reported in patients with childhood or infantile HPP but have never been described together in one patient: c.1171C > T (p.Arg391Cys) and c.1077C > G (p.Ile359Met) [10, 14, 15].
The diagnosis of HPP was confirmed biochemically (elevated serum pyridoxine phosphate and urine phosphoethanolamine) and with TNSALP mutation analysis (2 missense mutations identified).
In this case, mutational testing revealed that the patient is most likely a compound heterozygote with 2 heterozygous, missense mutations in the TNSALP gene.
In this study, we aimed to examine the clinical and laboratory characteristics of HPP cases and heterozygote carriers with normal laboratory findings, including TNSALP levels.
Identification of fifteen novel mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene in European patients with severe hypophosphatasia.
The clinical severity is associated with the age at diagnosis and the lack of TNSALP activity, except for odontohypophosphatasia where only the teeth are affected.
Recently, clinical trials have been undertaken using recombinant human TNSALP especially in a small number of infants and young children with severe HPP as well as in juveniles and adults, with promising results for bones, and pulmonary and physical functions (18).
Perinatal hypophosphatasia: radiology, pathology and molecular biology studies in a family harboring a splicing mutation (648+1A) and a novel missense mutation (N400S) in the tissue-nonspecific alkaline phosphatase (TNSALP) gene.