FGF23-Related Hypophosphataemic Bone Disease

Metabolic skeletal dysplasias comprise an extensive group of diseases capable of causing changes, usually progressive, in the bone and are due to hereditary disorders in many cases. The diagnosis and treatment of these diseases are not without difficulty, both because of their rarity and their possible confusion with more common diseases. A paradigmatic case of these metabolic skeletal dysplasias is X-linked hypophosphataemic rickets, which causes phosphaturia, a condition that alters the phosphate–calcium metabolism balance consequently causing, among other conditions, skeletal deformities and short stature. The genetic advances in recent years allow a much more accurate diagnosis of this disease when suspected, making differential diagnosis easier with similar entities but whose real causes are different. A better understanding of the phosphate–calcium metabolism allows us to replace the symptomatic treatment currently available with one that involves rebalancing the excess of fibroblast growth factor 23 (FGF23) by using monoclonal antibodies. In November 2018, a symposium sponsored by Kyowa Kirin Pharmaceuticals took place in Madrid, in which national and international experts addressed several aspects of these rare kidney diseases. Some topics addressed were the present and future genetic diagnosis, the use of multi-gene panels in renal or skeletal diseases, the role of animal models to better understand underlying skeletal changes, and the role of conventional radiology and surgery in the diagnosis and final treatment of bone deformities; all these without forgetting the important role of FGF23 and Klotho imbalances that result in the genetic change causing this disease. The optimization and limitations of conventional treatments currently available was also a topic addressed extensively, as well as the implications that new treatments against FGF23 could have in the future. This article is based on previously conducted studies and does not contain any new studies with human participants or animals performed by the author.