Early clinical and radiographic characteristics in fibrodysplasia ossificans progressiva: a report of two cases

Clinical Aspects and Current Therapeutic Approaches for FOP

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare heritable disorder of connective tissues characterized by progressive heterotopic ossification in various skeletal sites. It is caused by gain-of-function mutations in the gene encoding activin A receptor type I (ACVR1)/activin-like kinase 2 (ALK2), a bone morphogenetic protein (BMP) type I receptor. Heterotopic ossification is usually progressive leading to severe deformities in the trunk and extremities. Early clinical diagnosis is important to prevent unnecessary iatrogenic harm or trauma. Clinicians should become aware of early detectable skeletal malformations, including great toe deformities, shortened thumb, neck stiffness associated with hypertrophy of the posterior elements of the cervical spine, multiple ossification centers in the calcaneus, and osteochondroma-like lesions of the long bones. Although there is presently no definitive medical treatment to prevent, stop or reverse heterotopic ossification in FOP, exciting advances of novel pharmacological drugs focusing on target inhibition of the activated ACVR1 receptor, including palovarotene, REGN 2477, rapamycin, and saracatinib, have developed and are currently in clinical trials.

Characteristic calcaneal ossification: an additional early radiographic finding in infants with fibrodysplasia ossificans progressiva

BACKGROUND

We have clinically encountered children with fibrodysplasia ossificans progressiva who had abnormal calcaneal ossification.

OBJECTIVE

To evaluate whether calcaneal ossification variants are significant radiographic findings in children with fibrodysplasia ossificans progressiva.

MATERIALS AND METHODS

Lateral feet radiographs in nine children who fulfilled the diagnostic criteria of fibrodysplasia ossificans progressiva were reviewed. The studies were obtained during infancy or early childhood.

RESULTS

Fourteen lateral foot radiographs of fibrodysplasia ossificans progressiva were available for this study (ages at examination: 1-104 months). Four children ages 2 months to 11 months showed double calcaneal ossification centers; 7 children had plantar calcaneal spurs that decreased in size with age. Overall, eight of nine children with fibrodysplasia ossificans progressiva demonstrated double calcaneal ossifications and/or plantar calcaneal spurs in infancy or childhood.

CONCLUSION

Double calcaneal ossification centers in early infancy and plantar calcaneal spurs in childhood are frequently seen in children with fibrodysplasia ossificans progressiva and may be a useful radiologic indicator for early diagnosis.

Quality of life of patients with fibrodysplasia ossificans progressiva

INTRODUCTION

Fibrodysplasia ossificans progressiva (FOP) is a rare disorder characterized by episodes of acute pain and heterotopic ossification of soft tissue, and progressively limited physical function and social participation.

OBJECTIVE

We aimed to determine the impact of FOP on quality of life, specifying areas or dimensions most affected.

MATERIALS AND METHODS

This was a transverse observational study; patients with FOP were assessed using the Short Form 36. Questionnaire results were obtained using Quality Metric software and analyzed using frequency distribution, percentages and measures of central tendency.

RESULTS

Eight patients, mean age 30.2 years, were included. The physical dimension was the most affected, with an average of 25.5 points. The most representative items were impaired function and physical role. Physical pain was found with an average of 44.5 points. The best scores were reported in the areas of emotional role and mental health, with an average of 79 and 76 respectively.

CONCLUSIONS

FOP is a severely disabling disease, generating a significant deterioration in quality of life secondary to progressive deterioration in physical abilities. The findings of this study demonstrate good self-rated health of participants.

Radiographic characteristics of the hand and cervical spine in fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a disabling heritable disorder of connective tissue characterized by progressive heterotopic ossification in various extraskeletal sites. Early correct diagnosis of FOP is important to prevent additional iatrogenic harm or trauma. Congenital malformation of the great toes is a well-known diagnostic clue, but some patients show normal-appearing great toes. The thumb shortening and cervical spine abnormalities are other skeletal features often observed in FOP. This study aimed to address the quantitative assessment of these features in a cohort of patients with FOP, which potentially helps early diagnosis of FOP. Radiographs of the hand and cervical spine were retrospectively analyzed from a total of 18 FOP patients (9 males and 9 females) with an average age of 13.9 years (range 0.7-39.3 years). The elevated ratio of the second metacarpal bone to the distal phalanx of the thumb (> +1SD) was a consistent finding irrespective of the patient's age and gender. Infant FOP patients, in addition, exhibited an extremely high ratio of the second metacarpal bone to the first metacarpal bone (> +3SD). The height/depth ratio of the C5 vertebra increased in patients over 4 years of age (> +2SD). Additionally, the ratio of (height+depth) of the C5 spinous process to the C5 vertebral depth was markedly elevated in young patients (> +2SD). We quantitatively demonstrated the hand and cervical spine characteristics of FOP. These findings, which can be seen from early infancy, could be useful for early diagnosis of FOP even in patients without great toe abnormalities.

A novel mutation of ALK2, L196P, found in the most benign case of fibrodysplasia ossificans progressiva activates BMP-specific intracellular signaling equivalent to a typical mutation, R206H

Fibrodysplasia ossificans progressiva (FOP) is a rare autosomal dominant congenital disorder characterized by progressive heterotopic ossification in muscle tissues. Constitutively activated mutants of a bone morphogenetic protein (BMP) receptor, ALK2, have been identified in patients with FOP. Recently, a novel ALK2 mutation, L196P, was found in the most benign case of FOP reported thus far. In the present study, we examined the biological activities of ALK2(L196P) in vitro. Over-expression of ALK2(L196P) induced BMP-specific activities, including the suppression of myogenesis, the induction of alkaline phosphatase activity, increased BMP-specific luciferase reporter activity, and increased phosphorylation of Smad1/5 but not Erk1/2 or p38. The activities of ALK2(L196P) were higher than those of ALK2(G356D), another mutant ALK2 allele found in patients with FOP and were equivalent to those of ALK2(R206H), a typical mutation found in patients with FOP. ALK2(L196P) was equally or more resistant to inhibitors in comparison to ALK2(R206H). These findings suggest that ALK2(L196P) is an activated BMP receptor equivalent to ALK2(R206H) and that ALK2(L196P) activity may be suppressed in vivo by a novel molecular mechanism in patients with this mutation.