BONE MINERALIZATION IN AN OSTEOGENESIS IMPERFECTA MOUSE MODEL STUDIEDBY SMALL-ANGLE X-RAY-SCATTERING

We have studied the size and orientation of mineral crystals in cortic al bone of oim/oim mice, which are known to produce only alpha 1(I) co llagen homotrimers and which may serve as a model for human osteogenes is imperfecta. Long bones (femur and tibia) from young (5 wk old) oim/ oim mice and from unaffected heterozygous counterparts were investigat ed by small-angle x-ray scattering (SAXS), which is sensitive to struc tures smaller than 50 nm. Mineral crystals were compared in terms of t heir thickness and their alignment with respect to the long bone axis. While electron microscopic tomography has recently shown the existenc e of large mineral blocks (with all dimensions typically exceeding 50 nm) in mineralized tendons of oim/oim mice, SAXS revealed a family of thin, possibly needle-like, crystals in cortical bone. These crystals were similar in shape to those observed previously in normal mice, but they were thinner and less well aligned in oim/oim mice relative to h eterozygotes. Moreover, the crystal thickness and their alignment with the bone axis were more variable in oim/oim bone, with a close correl ation (r = 0.94, P < 0.001) between the two parameters. The presence o f smaller crystals with more variable alignment in corticalis of oim/o im mice may contribute to the brittleness of their bone, similar to th at of human osteogenesis imperfecta.