Collagen, genes and the skeletal dysplasias on the edge of a new era: a review and update.

This article reviews the newly described biochemical (type I and II collagen) abnormalities and specific gene defects in the skeletal dysplasias. The model of the collagen molecule is described and how collagen is processed from procollagen, where and how abnormalities occur, and the types of abnormalities produced (quantitative and qualitative). The only known type I collagen defects producing skeletal dysplasias--osteogenesis imperfecta, as well as the 'family' of established type II collagen disorders--achondrogenesis type II, hypochondrogenesis and spondyloepiphyseal dysplasia congenita are discussed. Finally, using case presentations, the practical approach to these disorders is shown. The importance of these investigations and the subsequent reevaluation of the clinical and radiological findings of specifically delineated skeletal dysplasias are discussed.