François Fassier

Delayed osteotomy but not fracture healing in pediatric osteogenesis imperfecta patients receiving pamidronate.

This study evaluated factors influencing fracture (n = 197) and osteotomy (n = 200) healing in children with moderate to severe OI. Pamidronate treatment was associated with delayed healing after osteotomy, but not after fracture. The data suggest that both pamidronate and mechanical factors influence bone healing in this cohort.

Complications of limb-lengthening in children who have an underlying bone disorder

We retrospectively reviewed the results, particularly with regard to complications, of lengthening of long bones in eight children (nine limb segments) who had a limb-length discrepancy secondary to an underlying bone disorder (Group 1). The mean age of these patients was twelve years (range, six to sixteen years), the mean preoperative limb-length discrepancy was 6.0 centimeters (range, 2.7 to 8.8 centimeters), and the mean lengthening of the nine limb segments was 6.2 centimeters (range, 2.7 to 9.0 centimeters). Only two extremities were equalized. We compared the results in Group 1 with those of limb-lengthening in seven children (nine limb segments) who had a discrepancy secondary to post-traumatic growth arrest (Group 2) and seven children (seven limb segments) who had a discrepancy secondary to growth arrest following an infection in the bone (Group 3). All of the procedures were performed at our institution during the same time-period by the same surgeons. There were forty-one complications (twenty-five minor and sixteen major), with a mean of five complications per limb segment, in Group 1; twenty-six complications (twenty minor and six major), with a mean of three complications per limb segment, in Group 2; and twenty-two complications (fourteen minor and eight major), with a mean of three complications per limb segment, in Group 3. The results in Group 1 suggest that the Ilizarov technique for lengthening, although effective in restoring the length of the extremity, is associated with a higher rate of complications in patients who have a discrepancy due to an underlying bone disorder than in those who have a discrepancy due to growth arrest. Therefore, caution should be exercised before a lengthening procedure is recommended for a patient who has an underlying bone disorder.

Intravenous Bisphosphonate Therapy of Young Children with Osteogenesis Imperfecta: Skeletal Findings During Follow Up Throughout the Growing Years

Cyclical intravenous bisphosphonate therapy is widely used to treat children with osteogenesis imperfecta (OI), but little is known about long‐term treatment outcomes. We therefore reviewed 37 children with OI (OI type I, n = 1; OI type III, n = 14; and OI type IV, n = 22) who started intravenous bisphosphonate therapy before 5 years of age (median 2.2 years; range, 0.1 to 4.8 years), and who had a subsequent follow‐up period of at least 10 years (median 14.8 years; range, 10.7 to 18.2 years), during which they had received intravenous bisphosphonate treatment (pamidronate or zoledronic acid) for at least 6 years. During the observation period, the mean lumbar spine areal bone mineral density Z‐score increased from –6.6 (SD 3.1) to –3.0 (SD 1.8), and weight Z‐score increased from –2.3 (SD 1.5) to –1.7 (SD 1.7) (p < 0.001 and p = 0.008). At the time of the last assessment, patients with OI type IV had significantly higher height Z‐scores than a control group of patients matched for age, gender, and OI type who had not received bisphosphonates. Patients had a median of six femur fractures (range, 0 to 18) and five tibia fractures (range, 0 to 17) during the follow‐up period. At baseline, 35% of vertebra were affected by compression fractures, whereas only 6% of vertebra appeared compressed at the last evaluation (p < 0.001), indicating vertebral reshaping during growth. Spinal fusion surgery was performed in 16 patients (43%). Among the 21 patients who did not have spinal fusion surgery, 13 had scoliosis with a curvature ranging from 10 to 56 degrees. In conclusion, long‐term intravenous bisphosphonate therapy was associated with higher Z‐scores for lumbar spine areal bone mineral density and vertebral reshaping, but long‐bone fracture rates were still high and the majority of patients developed scoliosis.

Homozygosity for Frameshift Mutations in XYLT2 Result in a Spondylo-Ocular Syndrome with Bone Fragility, Cataracts, and Hearing Defects

Heparan and chondroitin/dermatan sulfated proteoglycans have a wide range of roles in cellular and tissue homeostasis including growth factor function, morphogen gradient formation, and co-receptor activity. Proteoglycan assembly initiates with a xylose monosaccharide covalently attached by either xylosyltransferase I or II. Three individuals from two families were found that exhibited similar phenotypes. The index case subjects were two brothers, individuals 1 and 2, who presented with osteoporosis, cataracts, sensorineural hearing loss, and mild learning defects. Whole exome sequence analyses showed that both individuals had a homozygous c.692dup mutation (GenBank: NM_022167.3) in the xylosyltransferase II locus (XYLT2) (MIM: 608125), causing reduced XYLT2 mRNA and low circulating xylosyltransferase (XylT) activity. In an unrelated boy (individual 3) from the second family, we noted low serum XylT activity. Sanger sequencing of XYLT2 in this individual revealed a c.520del mutation in exon 2 that resulted in a frameshift and premature stop codon (p.Ala174Profs(∗)35). Fibroblasts from individuals 1 and 2 showed a range of defects including reduced XylT activity, GAG incorporation of (35)SO4, and heparan sulfate proteoglycan assembly. These studies demonstrate that human XylT2 deficiency results in vertebral compression fractures, sensorineural hearing loss, eye defects, and heart defects, a phenotype that is similar to the autosomal-recessive disorder spondylo-ocular syndrome of unknown cause. This phenotype is different from what has been reported in individuals with other linker enzyme deficiencies. These studies illustrate that the cells of the lens, retina, heart muscle, inner ear, and bone are dependent on XylT2 for proteoglycan assembly in humans.

Activities and participation in young adults with osteogenesis imperfecta.

The objective of this cross-sectional study was to compare the activities and participation in the domains of mobility, self-care, domestic life and social functioning in young adults according to osteogenesis imperfecta (OI) type. Fifty-four former OI patients were invited to participate and were sent a structured questionnaire. Twenty-four patients (mean age: 25.0 years, SD: 2.6 years) with OI types I (n=7), III (n=7), IV (n =8) and V (n=2) completed the questionnaire. Participants with OI type I reported full independence, and only few respondents with OI types IV and V reported some limitations in mobility and domestic life activities. Young adults with OI type III had significantly lower activity scores in aspects of mobility and domestic life and lower levels of participation in employment, sporting activities and transportation. Participation in leisure and social interactions were not different across OI types. Young adults with more severe types of osteogenesis imperfecta have greater activity limitations and participation restrictions. Our findings indicate the importance of promoting and facilitating involvement in meaningful activities and roles in young adults with moderate to severe forms of OI.

High prevalence of coxa vara in patients with severe osteogenesis imperfecta.

The purpose of this study was to determine the incidence and clinical presentation of coxa vara in 283 patients with osteogenesis imperfecta (OI). The charts and x-rays of 150 girls and 133 boys with OI were reviewed. The patients were classified according to the Sillence classification modified by Glorieux: 94 type I, 90 type IV, 67 type III, 18 type V, 10 type VI, and 4 type VII. The mean age was 9.4 years (range 0.3-23.3). Twenty-nine patients (10.2%) had coxa vara (23 left and 20 right). Fifty-five percent of them were type III, 24% type IV, 13.8% type VI, and 3.4% each of types V and VII. The incidence of coxa vara was 6% in type V, 8% in type IV, 24% in type III, 25% in type VII, and 40% in type VI (P < 0.001 for difference between types I, III, and IV). The mean neck-shaft angle was 99 degrees (range 80-110 degrees), the average head-shaft angle was 104 degrees (range 90-120 degrees), and the mean Hilgenreiner-epiphyseal angle was 68 degrees (range 40-90 degrees). Twenty-five patients (36 hips) had previous femoral rodding before diagnosis and seven hips (all type III) had no history of rodding. Abduction and internal rotation of the hip joints were restricted in all patients with this deformity. All children with coxa vara had a Trendelenburg gait. In conclusion, coxa vara in OI is not rare, especially in severe forms of the disease. Regular clinical and radiologic follow-up is indicated in children with previous femoral rodding and in severely affected children, particularly those with OI type III.

Osteotomy Healing in Children With Osteogenesis Imperfecta Receiving Bisphosphonate Treatment

A decade ago our group had reported that osteotomy healing was commonly delayed in children with moderate to severe osteogenesis imperfecta (OI) who were treated with intravenous pamidronate infusions. We subsequently maintained a bisphosphonate infusion–free interval of 4 months after osteotomy and changed the surgical approach (use of an osteotome instead of a power saw). In addition, zoledronic acid has become the standard intravenous bisphosphonate for treatment of OI at our institution. In the present study, we compared osteotomy healing before and after these changes were instituted. We evaluated bone healing post‐osteotomy on standard radiographs after 261 intramedullary rodding procedures involving osteotomies (139 femur, 112 tibia) in 110 patients (age at surgery 1.2 to 20.4 years). Delayed healing was diagnosed when the osteotomy line was visible 12 months after the event. We observed delayed bone healing after 48 of the 114 osteotomies (42%) performed with the new approach, and in 106 of the 147 osteotomies (72%) using the previous approach (p = 0.001). The odds for delayed osteotomy healing were significantly lower with the new approach even after adjustment for age, sex, height Z‐score, weight Z‐score, OI type, and bone involved (odds ratio = 0.17; 95% confidence interval 0.16–0.47). Thus, delayed osteotomy healing occurred less frequently in the past 10 years than in the decade before that. It is likely that this improved result is attributable to the implemented changes in both medical and surgical management.

Radial Head Dislocation and Subluxation in Osteogenesis Imperfecta

BACKGROUND Upper limb deformity in children with osteogenesis imperfecta may substantially impair function. The aims of this retrospective work were to study the prevalence of radial head malalignment (dislocation or subluxation) in different types of osteogenesis imperfecta and to identify factors linked to it. METHODS We assessed 489 upper limbs from 254 patients (with a mean age of 9.6 years and including 130 female patients) who had various types of osteogenesis imperfecta. Radiographs representing a single time-point for each patient were assessed for the presence and direction of radial head malalignment and associated abnormalities (dysplasia of the capitellum or of the radial head or neck, calcification of the interosseous membrane, or radioulnar synostosis). Deformations of the humerus, radius, and ulna were assessed with regard to location, direction, and magnitude. The forearm range of motion in pronation and supination and the hand grip force were measured in a subset of patients. RESULTS We observed radial head dislocation or subluxation in forty-four and thirty-nine upper extremities, respectively. The frequency of radial head malalignment was significantly higher in type-V osteogenesis imperfecta (86%) than in the other types (0% to 29%) (p < 0.001). Dysplasia of the humeral capitellum, radial head, or radial neck was associated with malalignment in all types of osteogenesis imperfecta, with the exception of capitellum dysplasia in type V. Malalignment in type V was associated with calcification of the interosseous membrane, an abnormality that was specific for type V. In the other osteogenesis imperfecta types, malalignment was commonly linked with radial and ulnar deformation and was associated with decreased forearm range of motion in supination and pronation and a lower grip force. CONCLUSIONS Radial head malalignment is common in osteogenesis imperfecta, especially in type V. Malalignment is associated with bowing characteristics and impaired function of the upper limb. These findings may provide support for surgical correction of radial and ulnar bowing in selected patients with osteogenesis imperfecta.

Topological Mapping of BRIL Reveals a Type II Orientation and Effects of Osteogenesis Imperfecta Mutations on Its Cellular Destination

BRIL/IFITM5 is a membrane protein present almost exclusively in osteoblasts, which is believed to adopt a type III (N‐out/C‐out) topology. Mutations in IFITM5 cause OI type V, but the characteristics of the mutant protein and the mechanism involved are still unknown. The purpose of the current study was to re‐assess the topology, localization, and biochemical properties of BRIL and compare it to the OI type V mutant in MC3T3 osteoblasts. Immunofluorescence labeling was performed with antibodies directed against BRIL N‐ or C‐terminus. In intact cells, BRIL labeling was conspicuously detected at the plasma membrane only with the anti‐C antibody. Detection of BRIL N‐terminus was only possible after cell permeabilization, revealing both plasma membrane and Golgi labeling. Trypsinization of live cells expressing BRIL only cleaved off the C‐terminus, confirming that it is a type II protein and that its N‐terminus is intracellular. A truncated form of BRIL lacking the last 18 residues did not appear to affect localization, whereas mutation of a single leucine to arginine within the transmembrane segment abolished plasma membrane targeting. BRIL is first targeted to the endoplasmic reticulum as the entry point to the secretory pathway and rapidly traffics to the Golgi via a COPII‐dependent pathway. BRIL was found to be palmitoylated and two conserved cysteine residues (C52 and C53) were critical for targeting to the plasma membrane. The OI type V mutant BRIL, having a five residue extension (MALEP) at its N‐terminus, presented with exactly the same topological and biochemical characteristics as wild type BRIL. In contrast, the S42 > L mutant BRIL was trapped intracellularly in the Golgi. BRIL proteins and transcripts were equally detected in bone from a patient with OI type V, suggesting that the cause of the disease is a gain of function mediated by a faulty intracellular activity of the mutant BRIL.

Functional analysis of upper limb deformities in osteogenesis imperfecta.

The charts and radiographs of 159 children with osteogenesis imperfecta (OI) were retrospectively reviewed to measure the severity of upper limb deformities and to evaluate the functional outcome using the Pediatric Evaluation of Disability Inventory (PEDI). The patients were classified according to the Sillence classification modified by Glorieux: 51 type 1, 33 type 3, 54 type 4, and 21 5ype 5. Fifty-nine patients (37.1%) had deformities of their upper limbs. Children with type 3 OI had the highest incidence and the most severe deformities. The humerus was the most commonly involved bone, followed by the ulna and radius. Upper limb deformities were classified into four groups according to the severity of the maximum deformity angle. The mean self-care scores of PEDI were significantly low only in the group with severe deformities, but mobility scores were dramatically decreased in both the moderate and severe deformity groups. Therefore, upper limb deformities in children with OI do not represent only a cosmetic problem, but may also significantly impair functional activities of daily living.