ALPL and hypophosphatasia: TNSALP also converts pyridoxal 5’-phosphate (PLP) to PL so that the active metabolite of vitamin B6 can pass through the cell membrane.[1] Patients with HPP show clinical features such as skeletal hypomineralization, hypercalcemia, vitamin B6-dependent convulsion, muscular hypotonia, failure to thrive, and developmental delay.