Fig. 1

Clinical and histologic characteristics of Hypophosphatasia (HPP). Stress fractures and bone marrow edemas are typical musculoskeletal manifestations of HPP. a Stress fracture of the right femur diaphysis. b Stress fracture of the right second metatarsale bone. c Histological section of a bone biopsy of the os pubis in Toluidine blue staining. Mineralized bone is shown in dark blue. The arrow is showing a thick layer of non-mineralized bone (osteoid) in light blue in the sense of osteomalacia. d Typical dental changes with discoloration of teeth due to hypomineralization. e and f The reduced muscle strength can be objectified using a hand dynamometer. In the example, the patient shows a reduced hand strength (HK) on the left by 3 standard deviations (SD) below the age- and gender-specific reference values