Fibrodysplasia ossificans progressiva: genetic and clinical characterization in a cohort of Polish patients and review of potential therapies.

Fibrodysplasia ossificans progressiva (FOP; OMIM #135100) is a rare genetic disorder characterized by congenital malformation of the great toes and progressive heterotopic ossification of soft tissues. To date, the disease has been linked to 15 pathogenic variants in the ACVR1 gene, which encodes a type I receptor for bone morphogenetic proteins. Most patients with FOP carry a recurrent single-nucleotide substitution (c.617G>A; p.Arg206His) in the ACVR1 gene. The genotype-phenotype correlations for atypical pathogenic variants of ACVR1 are poorly understood. In this study, we report the largest population of Polish patients affected by FOP and analyze their phenotypes and genotypes. We screened the whole ACVR1 coding sequence of 16 patients affected by FOP to confirm the presence of pathogenic variants. Thirteen individuals carried the classic pathogenic variant (p.Arg206His) and had a classic or FOP-plus phenotype. In agreement with the findings of previous studies, one patient with a p.Gly356Asp pathogenic variant had a variant FOP phenotype. We point to an unusual phenomenon in two patients who carried atypical pathogenic variants (p.Gly356Asp and p.Arg258Ser) and displayed a classic FOP phenotype. Our study extends the understanding of FOP's genotype-phenotype correlation, suggesting that classic FOP phenotypes are associated with non-classic pathogenic variants. We also summarize the recent advances in drug development for this condition. Therefore, the study may be valuable for clinicians consulting patients with FOP.