Osteogenesis imperfecta: morphologic and biochemical studies of connective tissue

Extract: In iliac crest biopsies from 11 patients (ages from 4 to 22 years) with osteogenesis imperfecta, cortical thickness, osteoid width, and number of osteons were less than normal at all ages. Bone surface activity (formation and resorption), measured by quantitative microradiography, was lower than normal in younger patients; the normal pubertal decrease in surface activity was not evident in patients with osteogenesis imperfecta and, consequently, bone surface activity in the older patients was higher than in age-matched normal subjects. The ultrastructure of osteocytes, bone collagen, and scleral collagen did not differ from normal; corneal collagen fibers, however, were approximately half the diameter of normal. Total urinary hydroxyl-proline excretion, measured in 11 patients, was below normal in all except 2 infants (less than 12 months old). Serum parathyroid hormone levels, measured in nine patients, were normal. Long term treatment with sodium fluoride (two patients) and treatment with magnesium oxide (three patients) did not alter bone morphology or bone surface activity. Speculation: The supposition that in osteogenesis imperfecta the connective tissue is characterized by an immature form of collagen was not substantiated by this study. The abnormal fibrillar pattern and paucity of collagen in various connective tissues suggest a qualitative defect, related to collagen maturation, as well as a quantitative deficit in the amount of collagen produced.