Fig. 4.

Severe osteopetrotic phenotype exhibited by Y750Q homozygous calves. (A) Dorsoventral radiographs of extended hind legs of a one-week-old homozygous mutant calf (MUT, right) and an age-matched Belgian Blue control calf (WT, left) are presented. X-rays were performed using a digital radiograph system [Vertix Vet (150 kV/600 mA), Siemens, Germany] with 75 kV and 100 mA as technical parameters. The bone marrow cavity is clearly visible within metatarsus of the wild-type calf but absent from the mutant corresponding bone (red arrows). The mutant calf also exhibits a tibia fracture (white arrow) probably consecutive to the acknowledged increased fragility of osteopetrotic long bones. (B) Fresh transversal (left) and sagittal (right) sections of long bones (tibia) of age-matched mutant (MUT) and control (WT) calves showing an absence of central bone marrow cavity for the mutant.