Childhood Osteoporosis and Presentation of Two Cases with Osteogenesis Imperfecta Type V

INTRODUCTION: Osteogenesis imperfecta (OI) is etiologically heterogeneous disorder characterized by childhood osteoporosis. A subtype OI type V is caused by the same c.-14C>T mutation in the IFITM5 gene. Nevertheless, there is a marked interindividual phenotypic variability in clinical presentation; however, response to bisphosphonates is reported to be good. METHODS: Two individuals with OI type V had multiple recurrent fractures with hypertrophic calluses, scoliosis and ossifications of the forearm interosseous membranes. Sequencing of IFITM5, genotyping of variants rs2297480 in farnesyl diphosphate synthase gene (FDPS), and rs3840452 in geranylgeranyl diphosphate synthase 1 gene (GGPS1), both involved in bisphosphonate metabolism, was performed. RESULTS: In patient 1 BMD reached normal values during bisphosphonate treatment and remained normal four years after the treatment discontinuation. In patient 2 no increase in BMD after five years of bisphosphonate treatment was observed and callus formation continued. The c.-14C>T IFITM5 mutation in heterozygous state was detected in both individuals. Additionally, both patients carried FDPS variant rs2297480 in homozygous state, and were heterozygous for GGPS 1 variant rs3840452. CONCLUSIONS: The paper presents a short overview of childhood osteoporosis with a special emphasis on OI type V by presenting two cases. Both OI type V patients had identical disease-causing mutation, but marked interindividual phenotypic variability. The striking failure in response to bisphosphonate treatment in one of the patients could not be explained by the variants in genes involved in bisphosphonate metabolism.