A heterozygous mutation (617G->A; R206H) in the glycine-serine (GS) activation domain of the activin A receptor type 1 (ACVR 1) gene was found in all these individuals.2 This was also the most common mutation in previous case series reported from our centre in the past, but all these patients belonged to the paediatric age group at presentation.22 This remains the commonest mutation reported in FOP to date and was confirmed to be present in both our patients. The gene discussed is ACVR1; the disease is fibrodysplasia ossificans progressiva.