Jp. Cassella et al., AN ELECTRON-PROBE X-RAY MICROANALYTICAL STUDY OF BONE-MINERAL IN OSTEOGENESIS IMPERFECTA, Calcified tissue international, 56(2), 1995, pp. 118-122
A semiquantitative electron probe X-ray microanalytical (XRMA) techniq
ue, in conjunction with transmission electron microscopy, was used to
compare the calcium to phosphorus (Ca/P) molar ratios in calcium phosp
hate standards of known composition, in normal bone and in bone from p
atients with osteogenesis imperfecta (OI). Using a modified routine pr
ocessing and resin embedding schedule, the measured Ca/P molar ratio o
f calcium phosphates standards of known composition were found to corr
elate well with the Ca/P molar ratio based on their respective chemica
l formulae. This technique was then used to compare the Ca/P molar rat
io in normal human bone and in OI bone. The Ca/P ratio values for norm
al bone (Ca/P = 1.631) correlated well with those for chemically prepa
red hydroxyapatite (Ca/P = 1.602), but in bone from OI patients, the C
a/P molar ratio was significantly lower (Ca/P = 1.488). This study has
shown that there is a lower Ca/P molar ratio in OI bone compared with
normal, matched bone. This suggests that the mineral deviates from th
e carbanoapatite usually found in bone. Isomorphous substitutions in t
he carbanoapatite lattice could account for this although this study h
as neither proved nor disproved this. The altered bone mineral is anot
her factor that could contribute to the increased fracture rate observ
ed in OI.