[Osteogenesis imperfecta: clinical and genetic heterogeneity]

Osteogenesis imperfecta is a hereditary connective tissue disorder characterized primarily by fractures with no or small causal antecedent; in most patients this is a consequence of diminished or abnormal production of collagen type I. It is a clinically heterogeneous disorder: it has been proposed recently to classify osteogenesis imperfecta in types I-V on the basis of the clinical picture and radiology. It is also a genetically heterogeneous disorder; 90% of cases are due to autosomal dominant mutations, while the remaining 10% are due to autosomal recessive mutations or of unknown cause. Osteogenesis imperfecta type I and to a lesser extent type IV are important differential diagnostic considerations in case of suspicion of non-accidental injury (NAI). When osteogenesis imperfecta is suspected, DNA analysis of the dominant COL1A1 and COL1A2 genes is currently the starting point for laboratory diagnosis unless there are strong indications for a recessive cause. Protein analysis based on skin biopsy remains indicated in specific cases.