Tissue-nonspecific alkaline phosphatase (TNSALP) (TNSALP)

Tissue-nonspecific alkaline phosphatase (TNSALP), encoded by the ALPL gene, is a membrane-bound enzyme essential for skeletal mineralization (UniProt P05186). It functions by hydrolyzing extracellular substrates, most notably inorganic pyrophosphate (PPi), which is a potent inhibitor of hydroxyapatite crystal growth (Millán & Whyte, 2016). By reducing PPi levels, TNSALP allows for the proper deposition of calcium and phosphate in bone and teeth. It also plays a critical role in Vitamin B6 metabolism by dephosphorylating pyridoxal 5'-phosphate (PLP) to pyridoxal, which can then cross the blood-brain barrier (Mornet, 2018). Deficiencies in this enzyme lead to hypophosphatasia (HPP), a disorder characterized by rickets, osteomalacia, and potentially fatal seizures in infants (StatPearls, 2023). The primary therapeutic approach is enzyme replacement therapy using Asfotase alfa, which restores enzymatic activity and normalizes substrate levels to improve clinical outcomes (FDA, Strensiq Label).

Other names

ALPLTNAPAlkaline phosphatase, liver/bone/kidney typeAP-TNAPAlkaline phosphatase 2

Enzyme replacement therapy (Asfotase alfa) restores the hydrolysis of inorganic pyrophosphate (PPi) to inorganic phosphate (Pi), thereby promoting hydroxyapatite crystal formation and skeletal mineralization.