Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder characterized by congenital bilateral malformation of the large toe and progressive, extensive, and irreversible heterotopic ossification (HO) of soft tissues throughout the body, leading to severe disabilities. FOP is caused primarily by mutations in activin A receptor type 1 (ACVR1), also known as activin-like kinase 2 (ALK2), which encodes a receptor belonging to the bone morphogenetic protein (BMP) type I family. However, the continuous and complex process of HO in FOP is not yet fully understood, which has impeded the development of therapeutic drugs. Despite surgical removal of HO, which often results in recurrence and expansion of ossification, there is currently no definitive drug treatment available to completely prevent, halt, or reverse the progression of HO in FOP. Currently, researchers are intensively studying the pathogenesis of FOP at various stages and developing promising drug candidates, including saracatinib, palovarotene, and rapamycin. This review provides an overview of progress in understanding the mechanism of FOP and the development of therapeutic drugs, with the goal of providing insights for further research and the development of new treatment methods.
Myositis Ossificans/genetics* ; Humans ; Activin Receptors, Type I/genetics* ; Ossification, Heterotopic ; Mutation ; Sirolimus/therapeutic use* ; Quinolones/therapeutic use* ; Benzodioxoles/therapeutic use* ; Animals ; Quinazolines/therapeutic use*

Fibrodysplasia ossificans progressiva (FOP; OMIM 135100) is a rare but extremely disabling genetic disorder of the skeletal system, and is characterized by the progressive development of ectopic ossification of skeletal muscles and subsequent joint ankylosis. The c.617G>A; p.R206H point mutation in the activin A type I receptor (ACVR1) gene has been reported to be a causative mutation of FOP. In the present study, mutation analysis of the ACVR1 gene was performed in 12 patients diagnosed or suspected to have FOP. All patients tested had a de novo heterozygous point mutation of c.617G>A; p.R206H in ACVR1. Mutation analysis confirmed a diagnosis of FOP in patients with ambiguous features, and thus, could be used for diagnostic purposes. Early confirmation through mutation analysis would allow medical professionals to advise on the avoidance of provoking events to delay catastrophic flare-ups of ectopic ossifications.
Activin Receptors, Type I/*genetics ; Adolescent ; Adult ; Asian Continental Ancestry Group/*genetics ; Base Sequence ; Child ; Female ; Genetic Predisposition to Disease ; Heterozygote ; Humans ; Korea ; Male ; Myositis Ossificans/*diagnosis/genetics/radiography ; Point Mutation ; Young Adult

Fibrodysplasia ossificans progressiva (FOP; OMIM 135100) is a rare but extremely disabling genetic disorder of the skeletal system, and is characterized by the progressive development of ectopic ossification of skeletal muscles and subsequent joint ankylosis. The c.617G>A; p.R206H point mutation in the activin A type I receptor (ACVR1) gene has been reported to be a causative mutation of FOP. In the present study, mutation analysis of the ACVR1 gene was performed in 12 patients diagnosed or suspected to have FOP. All patients tested had a de novo heterozygous point mutation of c.617G>A; p.R206H in ACVR1. Mutation analysis confirmed a diagnosis of FOP in patients with ambiguous features, and thus, could be used for diagnostic purposes. Early confirmation through mutation analysis would allow medical professionals to advise on the avoidance of provoking events to delay catastrophic flare-ups of ectopic ossifications.
Activin Receptors, Type I/*genetics ; Adolescent ; Adult ; Asian Continental Ancestry Group/*genetics ; Base Sequence ; Child ; Female ; Genetic Predisposition to Disease ; Heterozygote ; Humans ; Korea ; Male ; Myositis Ossificans/*diagnosis/genetics/radiography ; Point Mutation ; Young Adult

OBJECTIVETo study the clinicopathologic features, diagnosis and differential diagnosis of myositis ossificans (MO).

METHODSThe clinical features, radiologic results and pathologic findings of 15 cases of MO (including biopsy and surgical specimens) were analyzed. The hematoxylin and eosin sections were reviewed under light microscope. Immunohistochemical staining for S-100 protein, vimentin, desmin, actin and osteonectin was performed.

RESULTSThe age of the patients ranged from 12 to 46 years. The male-to-female ratio was 11:4. Thirteen cases were located in the parosteum of long bone or subperiosteal soft tissue. The remaining two cases occurred in iliac region and palm, respectively. Five patients had history of injury, while 2 patients had operation before. Four patients had no history of trauma and the remaining one had unknown clinical history. Histologically, zonation pattern was not conspicuous in 10 biopsy cases and 8 corresponding surgical specimens. On the other hand, zonation pattern was observed in 5 biopsy cases and 7 corresponding surgical specimens. Follow up revealed relapses in two patients. Immunohistochemical study showed various degree of positivity for vimentin, desmin, actin and osteonectin. S-100 protein was focally positive in 2 of the cases. The Ki-67 index varied from 1% to 10%.

CONCLUSIONCorrect diagnosis of MO relies on correlation of clinical features, radiologic examination and pathologic findings.

Adolescent ; Adult ; Biopsy ; Child ; Female ; Humans ; Male ; Middle Aged ; Myositis Ossificans ; diagnosis ; genetics ; pathology ; S100 Proteins ; genetics ; Vimentin ; X-Rays ; Young Adult

OBJECTIVEFibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant inherited disease caused by mutations of ACVR1 gene and can be inherited from either mother or father. FOP is characterized by the presence of malformations of the big toes and of progressive extra-skeletal ossification. Direct sequence analyses of genomic DNA have demonstrated that there is an identical single nucleotide substitution (c617G-->A, R206H) in the glycine-serine (GS) activation domain of ACVR1 gene, responsible for all affected individuals reported so far. We report a Chinese girl with typical FOP characteristics, in whom the same mutation in ACVR1 was identified.

METHODSClinical diagnosis was based on physical examination, radiological findings, and biochemical tests. For mutation detection, peripheral blood was obtained with informed consent from the patient and the parents. Genomic DNA was extracted from peripheral blood using standard method. Exon 4 of ACVR1 was amplified by polymerase chain reaction (PCR), and the PCR products were subjected to automatic DNA sequencing.

RESULTSThe affected girl is 3-year-old and showed typical clinical manifestations of FOP. She had malformations of the halluces at birth and subsequently progressive extra-skeletal ossification developed at the age of 8 - 9 months. Then, she gradually developed stiffness of the knee joint and neck but remained ambulant. Radiographic changes were observable, e.g., the extra-skeletal ossification was found at cervical spine. Her mother has congenital malformations of the halluces, but had no postnatal progressive extra-skeletal ossification. Her father and other family members are normal. With direct sequencing of the PCR products, a G to A substitution at c617 of ACVR1 (R206H) was detected in the patient only but not in her parents. Paternity analysis suggested that it is a de novo mutation.

CONCLUSIONThis is the first case reported in a Chinese patient with FOP in the mainland of China, which was confirmed by direct sequencing. Although sporadic cases of FOP have been reported in diverse geographic and ethnic group, the mutations of ACVR1 c617 (R206H) are identical up to now. The presence of mutation hot spot facilitates molecular diagnosis in clinical practice. Genetic detection is important for FOP patients to avoid misdiagnosis and further damages, including those from medical intervention.

Activin Receptors, Type I ; genetics ; Asian Continental Ancestry Group ; genetics ; Base Sequence ; Child, Preschool ; Female ; Humans ; Molecular Sequence Data ; Myositis Ossificans ; genetics ; Point Mutation ; Sequence Analysis, DNA