Autosomal dominant osteopetrosis: Bone mineral measurements of the entire skeleton of adults in two different subtypes

Abstract

Bone mineral content (BMC) and density (BMD) were measured by dual-energy X-ray absorptiometry in two subtypes of autosomal dominant osteopetrosis (ADO). Both types have been radiologically characterized by diffuse symmetrical osteosclerosis, but with characteristic differences. Increased thickness of the cranial vault is a typical finding in type I ADO, whereas endobones in the pelvis and end-plate thickening in the spine are obligate findings in type II. Eleven patients with type I from three kindreds, and seven patients with type II, one family participated in the study, and were compared with 18 age- and sex-matched normal controls. Whole-body BMC and BMD were measured, and regions of special interest were selected: head, axial, and appendicular skeleton. Moreover, lumbar spine and femoral neck scans were performed. Whole-body BMC and BMD, mostly reflecting cortical bone, were markedly increased in both types compared with normals. A pronounced osteosclerosis was present in the axial as well as the appendicular skeleton. Median BMD was markedly increased in the axial skeleton by 51% (44–56) and 42% (33–56), (median differences with 95% CI), respectively, for types I and II compared to normal controls, and in the appendicular skeleton by 48% (37–59) and 38% (16–45). No overlap between observed ranges of patients and controls was observed. A positive correlation between age and whole-body BMD was demonstrated in ADO, but not in the control group, indicating progressive osteosclerosis with age. Median BMD of the lumbar spine, which mostly reflects trabecular bone, showed increased densities in both types, 71% (51–84) and 59% (37–93), respectively. The findings substantiate the clinical and radiographic impression of the disease with progressive osteosclerosis, and more pronounced symptoms in the elderly patients. The study demonstrates a quantitation of the degree of osteosclerosis in ADO; it is concluded that measurements of BMC and BMD complete radiologic examinations.