Osteogenesis imperfecta type III. Delineation of the phenotype with reference to genetic heterogeneity.

The existence of a rare form of osteogenesis imperfecta, OI type III, has been postulated. This is characterized by autosomal recessive inheritance with neonatal manifestations of bone fragility or deformability. It is usually nonlethal. Studies of some 345 pedigrees of OI in the last 8 years confirm that patients falling into this group are rare. They should be distinguished as a special group within the group of OI subjects with a progressively deforming OI phenotype delineated in previous publications [Sillence et al, 1979a, b]. The OI type III phenotype does not necessarily equate with progressively deforming OI, and probably only a proportion of cases with severe deformity and normal sclerae have OI type III. On the other hand, distinction between these patients and those with a milder form of perinatally lethal OI type II might be difficult. Whereas the natural history of skeletal deformity and fractures in patients with OI type III has certain similarities, variable severity between families indicates that OI type III is likely to be genetically heterogeneous.