Fibrodysplasia ossificans progressiva (FOP) is a rare but very severe disease, 
characterised by congenital malformations of the toes and by progressive 
heterotopic ossification of muscles and joints. Two genes, the noggin (NOG) gene 
and the activin A type I receptor (ACVRI) gene, are involved in FOP. In this 
study we have searched for the NOG and the 617G>A (ACVR1) mutations in a well 
characterized series of twenty-seven French FOP patients. Five NOG mutations 
(delta 42, 274G>C, 275G>A, 276G>A, and 283G>A) have been found in seven (26%) of 
our FOP patients. The 617G>A mutation in the ACVR1 gene is found in fourteen 
(52%) of the patients. With one exception (patient number 22), 617G>A and NOG 
mutations are mutually exclusive in patients. Mutations 274G>C, 283G>A and 
617G>A segregate with the trait in five different FOP families, some members of 
them being partially affected by the disease.