What is it about?

Multiple osteochondromas is a rare disorder, characterized by bony benign tumours, named osteochondromas, arising from long bones. These protuberances increase during growth until skeletal maturity, frequently causing deformities and limitations. Our study aims to analyse the data collected by the Registry of Multiple Osteochondromas, to refine a previous classification proposed by us in 2013 and to provide a representative picture of the clinical manifestations throughout the lifespan. Patients were grouped following the IOR Classification, which identifies 3 patients' classes based on the presence/absence of deformities and/or limitations. Each class were subdivided in two subclasses (A and B) according to the number of bony tumours, deformities, and limitations. We evaluated 968 patients: 243 children (<10 years), 136 adolescents (10–15 years), and 589 adults. Of the entire population, half patients presented at least one deformity, and one quarter reported at least one limitation. Compared with our previous study, the number of children was more than doubled and the percentage of mild/moderate cases was notably increased, giving a better disease overview of the disease. The increased number of young patients and of the overall population suggested us a different cut-off for dividing Class II in subclasses. We confirmed that Multiple osteochondromas is characterized by huge clinical variability, from very mild case to complex manifestations, suggesting that an early classification of the disease may offer a useful tool to follow disease evolution, to support clinical practice, and to propose timely interventions.

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Why is it important?

There is a lack of knowledge, treatment, and care about rare diseases like Multiple osteochondromas. Our findings support the definition of a representative picture of the clinical manifestations of this disease throughout the lifespan.


This article required a long journey and the participation of multidisciplinary expertise, including clinicians, geneticists, nurses, statisticians, and researchers. This would not have been possible without the engagement of patients, their families, and the support of the Patients' Association. In our opinion, IOR classification is an effective tool both for routine disease management and for further research studies and projects.

Dr. Manila Boarini
IRCCS Istituto Ortopedico Rizzoli

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This page is a summary of: The Rizzoli Multiple Osteochondromas Classification revised: describing the phenotype to improve clinical practice, American Journal of Medical Genetics Part A, September 2021, Wiley, DOI: 10.1002/ajmg.a.62470.
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