[Bones and bone marrow of the newborn " op " osteopetrotic rat, and the early diagnosis of the disease].

It is possible to make an early diagnosis of rat " op " osteopetrosis. The growth of the mandibular incisor is stopped at birth by failure of bone resorption around the dental root. The primary trabeculae of the long bones fail to undergo resorption: osteoblasts differentiate along them, but osteoclasts are missing and reticular cells are not distinguishable. When 2 and 3 days old, the medullary cavity is obstructed by osseous trabeculae, vascular system is lacking, hemopoietic cells no longer differentiate, osteoclasts are scarce and degenerative; medullary tissue is compact, including numerous osteoblastic cells. Bone marrow smears clearly show medullary cell deficiency, weakening hemopoiesis, prevalent osteoblasts and a lack of osteoclasts. Marrow is taken out "in vivo" from an excised metatarsal bone, at birth and over the next few days. Osteopetrotic rats identified in this way in litters issued from heterozygote pair can be treated from the first week.