Pathophysiology and therapeutic options in osteogenesis imperfecta: an update

Abstract

Osteogenesis imperfecta (OI) is a rare, heritable systemic disorder of bone and connective tissue, which in almost 90% of cases is due to mutations affecting the normal synthesis of type I collagen. In 1979, four OI phenotypes were categorized which were inherited as autosomal dominant characteristics. Individuals with OI present both genetic and phenotypic variabilities. Major characteristics of OI are bone fragility, blue sclerae, dentinogenesis imperfecta, short stature, scoliosis, and joint hyperextensibility. Both autosomal dominant and recessive inheritance are now recognized. Advances in molecular diagnosis have led to a major expansion in our understanding of the genetic basis for different OI phenotypes. To date, sequence variants in 17 genes are described as causative of OI. These genes regulate the synthesis of type I collagen pro-alpha polypeptide chains, proteins involved in type I collagen processing in the endoplasmic reticulum and proteins involved in osteoblast function. These new genetic associations have also led to uncertainty with regard to the current classification of OI phenotypes. Bisphosphonates have been widely used to improve bone mass and decrease fractures in both children and adults with OI. While effective in many but not all children when administered for 2–4 years, bisphosphonates have not proven effective in adults with OI. Studies are limited for treatment of adults with teriparatide and denosumab. Advances have been reported in the surgical management of OI. Although the role of physical therapy in the management of children and adults was previously described, this important treatment modality is significantly underutilized.