Fibrodysplasia Ossificans Progressiva in South Africa: Difficulties in Management in a Developing Country

Current and emerging treatment modalities for fibrodysplasia ossificans progressiva

INTRODUCTION

Heterotopic ossification (HO), acquired or hereditary, is a diverse pathological condition defined by the production of extraskeletal bone in muscles, soft tissues, and connective tissues. Acquired HO is relatively prevalent and develops mostly in response to trauma, although its etiology is unknown. Genetic forms provide insight into the pathobiological mechanisms of this disorder. Fibrodysplasia ossificans progressiva (FOP) is a rare hereditary form of HO that can have a significant impact on affected individuals. FOP steadily weakens affected subjects and increases their risk of death.

AREAS COVERED

The U.S. Food and Drug Administration has recently approved the retinoid palovarotene as the first compound to treat heterotopic ossification in patients with FOP. This review provides a comprehensive overview of current and potential future pharmacotherapeutic options and their modes of action. The online databases PubMed, Cochrane Library, Web of Science, and ClinicalTrials.gov were searched using the terms 'heterotopic ossification' and 'fibrodysplasia ossificans progressiva' or synonyms, with a special focus over the last 5 years of publications.

EXPERT OPINION

Approval of palovarotene, as the first retinoid indicated for reduction in the volume of new HO, may revolutionize the therapeutic landscape. However, long-term safety and efficacy data for palovarotene are currently lacking.

Fibrodysplasia ossificans progressiva: Diagnosis with ultrasound

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare connective tissue disease, diagnosed by genetic testing. This is the first report in English literature wherein an ultrasound examination suggested this specific diagnosis. In this case, a two month old girl presented with bi-parieto-occipital swellings that were being managed as subgaleal haematoma. The parents were anxious that there was no resolution of the swellings. The suspicion of FOP was raised during the ultrasound examination where a review of the images prompted a questioning of the parents about other lesions in the body. Ultrasound examination of a lump in the thigh revealed calcifications in the vastus lateralis muscle. The appearances on the ultrasound combined with the presence of hallucis valgi suggested a diagnosis of FOP. The diagnosis was subsequently confirmed by genetic studies. This case highlights the need for good communication between the physician, patient and the imaging department.

Fibrodysplasia ossificans progressiva in Spain: epidemiological, clinical, and genetic aspects

We aimed to investigate the epidemiological determinants, clinical features, and genetic pattern of FOP in our country by evaluating the entire population of patients identified according to a combination of methods. To achieve this, 24 individuals were confirmed as FOP cases, 17 of whom were alive at the end of 2011 (point prevalence=0.36 × 10(-6)). The gender distribution (male/female ratio=13/11) and the concurrent range of ages (from 4 to 53 years; mean ± SD: 30.2 ± 13.8) are in agreement with similar reports. Twenty-one (87.5%) had characteristic congenital malformations of the big toe, and short thumbs were found in 65.2% of cases. In addition, other skeletal malformations such us fusion of the posterior elements of the cervical spine (89.0%), knee osteochondromas (71%), scoliosis (54.5%), and short and broad femoral neck (52.6%) were observed. All had developed mature ossicles of heterotopic bone in typical anatomic and temporal patterns, ranging in number from 1 to 17 (9.5 ± 3.9). Age at appearance of first ossifying lesion varied from 3 months to 15 years. Mean age at diagnosis was 7.3 ± 5.1 years and the average delay in reaching the correct diagnosis after the onset of heterotopic ossification was 2.7 years (range=0-12 years). Biopsy of the pre-osseous lesions was performed in 11 of 20 (55.0%), providing no useful information for the diagnosis of FOP. Seven of 18 (38.9%) reported some hearing loss, and 5 (27.8%) experienced diffuse thinning of the hair or were bald. No patient had relatives with a typical FOP clinical picture. Fourteen of the 16 cases which were genetically investigated displayed the single heterozygous mutation c.617G>A in exon 4 of the ACVR1 gene. One of the two patients who did not present with the canonical ACVR1 mutation showed a heterozygous mutation c.774G>C in exon 5 leading to the substitution of Arginine 258 with a serine. The other patient had a heterozygous c.774G>T substitution in exon 5 leading to the same amino acid change (p.Arg258Ser). These two patients had only nonspecific abnormalities of the great toe, lacked the typical anatomic and developmental pattern of heterotopic ossification, and shared a trend toward uncommon clinical features. These results provide new insight on the epidemiological and clinical traits of FOP, reinforcing the notion of its worldwide homogeneity. The molecular characterization of ACVR1 sequence variation will contribute to the understanding of the genetic profile of this devastating disease in different geographical areas.