Classical and atypical Fibrodysplasia Ossificans Progressiva in India.

Fibrodysplasia Ossificans Progressiva (FOP) is a rare debilitating disorder characterized by congenital deformity of the great toes from infancy and postnatal heterotopic ossification. Activating mutations in the activin A receptor type 1 (ACVR1) gene are responsible for the disease. The most common allelic variant leading to FOP is c.617 G>A; p.R206H, however, other alleles have been reported with atypical phenotypes. We report 14 cases presenting to a referral institution in South India over a 3-year period. The patients were clinically diagnosed based on foot abnormality or abnormal ectopic ossification and were screened for ACVR1. The genetic analysis of ACVR1 identified the recurrent allelic variant in 12 of 14 patients. One of the remaining patients had a previously reported allele c.1067G>A; p.G356D in the 9th exon and the second allele c.983G>A; p.G328E in the 8th exon of ACVR1. The most common recurrent allele c.617 G>A; p.R206H is also the most common in Indian patients with FOP.