In 2006, five familial cases of FOP, with affected individuals showing both malformed toes and heterotopic ossification, were examined by genome-wide linkage analysis to identify the gene responsible for FOP; among these affected individuals, the heterozygotic single-nucleotide mutation c.617G>A was detected in the ACVR1 gene, which is located on chromosome 2q [1]. The gene discussed is ACVR1; the disease is fibrodysplasia ossificans progressiva.