Giacomo Venturi

Current and emerging treatments for the management of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is the most common bone genetic disorder and it is characterized by bone brittleness and various degrees of growth disorder. Clinical severity varies widely; nowadays eight types are distinguished and two new forms have been recently described although not yet classified. The approach to such a variable and heterogeneous disease should be global and therefore multidisciplinary. For simplicity, the objectives of treatment can be reduced to three typical situations: the lethal perinatal form (type II), in which the problem is survival at birth; the severe and moderate forms (types III–IX), in which the objective is ‘autonomy’; and the mild form (type I), in which the aim is to reach ‘normal life’. Three types of treatment are available: non-surgical management (physical therapy, rehabilitation, bracing and splinting), surgical management (intramedullary rod positioning, spinal and basilar impression surgery) and medical-pharmacological management (drugs to increase the strength of bone and decrease the number of fractures as bisphosphonates or growth hormone, depending on the type of OI). Suggestions and guidelines for a therapeutic approach are indicated and updated with the most recent findings in OI diagnosis and treatment.

Lack of expression of SERPINF1, the gene coding for pigment epithelium-derived factor, causes progressively deforming osteogenesis imperfecta with normal type I collagen

Osteogenesis imperfecta (OI) is a clinically heterogeneous heritable connective tissue disorder, characterized by low bone mass and reduced strength, which result in susceptibility to fracture and bone deformities. In most cases it is caused by dominant mutations in type I collagen genes, COL1A1 and COL1A2. Recessive forms, which collectively account for approximately 5% of cases of osteogenesis imperfecta detected in North America and Europe, are caused instead by mutations in various genes coding for proteins involved in collagen posttranslational modifications, folding, and secretion. A novel disease locus, SERPINF1, coding for pigment epithelium‐derived factor (PEDF), has been found recently. In SERPINF1 mutants described so far, synthesis, posttranslational modification, and secretion of type I collagen were reported to be normal. Here we describe three siblings born to consanguineous parents, who show an initially mild and then progressively worsening form of OI with severe deformities of the long bones. They are homozygous for a frameshift mutation in exon 4 of the SERPINF1 gene, which leads to lack of the transcription/translation product, likely a key factor in bone deposition and remodeling. Synthesis and secretion of type I collagen are normal. Clinical, radiographic, histological, and histomorphometric data from the proband are reminiscent of the distinctive features of type VI OI.

GH in combination with bisphosphonate treatment in osteogenesis imperfecta

OBJECTIVE To verify the effects of bisphosphonates (Bps) in combination with recombinant human GH (rGH) in pediatric osteogenesis imperfecta (OI) patients; we focused on possible improvement of bone mineral density (BMD), projected bone areas, growth velocity, and fractures risk. DESIGN A randomized controlled 1-year clinical trial on 30 prepubertal children (M:F=14:16) affected by OI (type I, IV, and III) being treated with neridronate. METHODS Following an observational period of 12 months during ongoing neridronate treatment, the patients were randomly divided into two groups: 15 were treated for 12 months with rGH and neridronate (group Bp+rGH) and 15 continued neridronate alone (group Bp). We evaluated auxological parameters, number of fractures, bone age (BA), bone metabolic parameters, and bone mass measurements (at lumbar spine and radius by dual-energy X-ray absorptiometry). RESULTS The mean variation in percentage of BMD (Delta%BMD)--at lumbar spine (L2-L4), at distal and ultradistal radius--and the projected area of lumbar spine increased significantly in group Bp+rGH (P<0.05). Growth velocity was significantly higher during rGH treatment in group Bp+rGH versus group Bp and versus pretreatment (P<0.05), with no difference in increase in BA or fracture risk rate. Patients with quantitative (-qt) collagen synthesis defects had a higher, although not significant, response to rGH in terms of growth velocity and BMD. CONCLUSIONS In OI patients, the combined rGH-Bp treatment may give better results than Bp treatment alone, in terms of BMD, lumbar spine projected area and growth velocity, particularly in patients with quantitative defects.

Osteogenesis imperfecta: clinical, biochemical and molecular findings

Mutations in COL1A1 and COL1A2 genes, encoding the α1 and α2 chain of type I collagen, respectively, are responsible for the vast majority of cases of osteogenesis imperfecta (OI) (95% of patients with a definite clinical diagnosis). We have investigated 22 OI patients, representing a heterogeneous phenotypic range, at the biochemical and molecular level. A causal mutation in either type I collagen gene was identified in 20 of them: no recurrent mutation was found in unrelated subjects; 15 out of 20 mutations had not been reported previously. In two patients, we could not find any causative mutation in either type I collagen gene, after extensive genomic DNA sequencing. Failure of COL1A1/COL1A2 mutation screening may be due, in a few cases, to further clinical heterogeneity, i.e. additional non‐collagenous disease loci are presumably involved in OI types beyond the traditional Sillence’s classification.

A novel splicing mutation in FKBP10 causing osteogenesis imperfecta with a possible mineralization defect

Osteogenesis imperfecta (OI) is a group of hereditary disorders characterized by bone fragility and osteopenia, with a broad spectrum of clinical severity. The majority of cases are dominantly inherited and due to mutations in type I collagen genes, whereas recessive forms are less frequent and attributable to mutations in different genes involved in collagen I post translational modifications and folding (prolyl-3-hydroxylase complex, SERPINH1, FKBP10). We report the case of a patient with an initially mild and then progressively severe form of osteogenesis imperfecta due to a novel homozygous splicing mutation in FKBP10 (intron 8 c.1399+1G>A), which results in aberrant mRNA processing and consequent lack of FKBP65 chaperone. Although this mutation does not affect collagen type I post translational modifications in dermal fibroblasts, the histomorphometric pattern of our patients bone sample showed a mineralization defect possibly due to the mutation in FKBP10.

Infantile cortical hyperostosis and COL1A1 mutation in four generations

Infantile cortical hyperostosis (ICH, OMIM 114000) is a rare familial disorder which affects infants. It spontaneously heals in the first years of life. The disease is characterized by regressive subperiosteal hyperosteogenesis mainly affecting long bones, mandible, clavicles, and ribs which are remarkably swollen and deformed on X-rays. But it is also important to take into consideration the autosomal dominant pattern of inheritance to detect it. In 2005 Gensure et al. detected 3040C→T mutation in COL1A1 gene in three unrelated ICH families. Four generations of patients belonging to the same family were examined in our study. Molecular testing has now disclosed a pathogenic mutation in nine of them. The patients spontaneously recovered. Although our paper shows a distinct correlation between R836C mutation and ICH, there is a certain interindividual and intra-familial variability.

Identification of a novel pax8 gene sequence variant in four members of the same family: from congenital hypothyroidism with thyroid hypoplasia to mild subclinical hypothyroidism.

BackgroundCongenital hypothyroidism is often secondary to thyroid dysgenesis, including thyroid agenesis, hypoplasia, ectopic thyroid tissue or cysts. Loss of function mutations in TSHR, PAX8, NKX2.1, NKX2.5 and FOXE1 genes are responsible for some forms of inherited congenital hypothyroidism, with or without hypoplastic thyroid. The aim of this study was to analyse the PAX8 gene sequence in several members of the same family in order to understand whether the variable phenotypic expression, ranging from congenital hypothyroidism with thyroid hypoplasia to mild subclinical hypothyroidism, could be associated to the genetic variant in the PAX8 gene, detected in the proband.MethodsWe screened a hypothyroid child with thyroid hypoplasia for mutations in PAX8, TSHR, NKX2.1, NKX2.5 and FOXE1 genes. We studied the inheritance of the new variant R133W detected in the PAX8 gene in the proband’s family, and we looked for the same substitution in 115 Caucasian European subjects and in 26 hypothyroid children. Functional studies were performed to assess the in vitro effect of the newly identified PAX8 gene variant.ResultsA new heterozygous nucleotide substitution was detected in the PAX8 DNA-binding motif (c.397C/T, R133W) in the proband, affected by congenital hypothyroidism with thyroid hypoplasia, in his older sister, displaying a subclinical hypothyroidism associated with thyroid hypoplasia and thyroid nodules, in his father, affected by hypothyroidism with thyroid hypoplasia and thyroid nodules, and his first cousin as well, who revealed only a subclinical hypothyroidism. Functional studies of R133W-PAX8 in the HEK293 cells showed activation of the TG promoter comparable to the wild-type PAX8.ConclusionsIn vitro data do not prove that R133W-PAX8 is directly involved in the development of the thyroid phenotypes reported for family members carrying the substitution. However, it is reasonable to conceive that, in the cases of transcriptions factors, such as Pax8, which establish several interactions in different protein complexes, genetic variants could have an impact in vivo.