Pharmacotherapy in Rare Skeletal Diseases

New therapeutic approaches have been established in the field of rare skeletal diseases (e.g., for osteogenesis imperfecta, achondroplasia, hypophosphatemic rickets, hypophosphatasia, and fibrodysplasia ossificans progressiva). After elucidation of the underlying genotypes and pathophysiologic alterations of these diseases, new treatment options have been designed. Most drugs are based on an interaction with the disease-specific cascade of enzymes and proteins involved in the disease. Thereby an approved treatment is available for children with severe forms of hypophosphatasia and hypophosphatemic rickets (asfotase alfa, burosumab). Additionally, there are different phase 3 trials ongoing assessing the efficacy and safety of drugs for osteogenesis imperfecta, achondroplasia, and fibrodysplasia ossificans progressiva (denosumab, vosoritide, palovarotene).Because all these diseases are rare, the number of investigated patients in the trials is small, and the knowledge about rare side effects and long-term outcome is limited. Therefore it is recommended to treat the patients in specialized centers where the effects of the drugs can be evaluated and data about safety, side effects, and efficacy can be collected.Based on the fact that most drugs for rare diseases are highly expensive clear indications for start of a treatment, evaluation of the therapy and recommendations how long a treatment has to be administrated are urgently needed.