Molecular Dissection of Somatic Skeletal Disease in Neurofibromatosis Type 1.

Neurofibromatosis type 1 (NF1) is a tumor predisposition syndrome caused by heterozygous NF1 gene mutations. Patients with NF1 present with pleiotropic somatic secondary manifestations, including development of bone pseudarthrosis after fracture. Somatic NF1 gene mutations were reproducibly identified in patient-derived pseudarthrosis specimens, suggesting a local mosaic cell population including somatic pathologic cells. The somatic cellular pathogenesis of NF1 pseudarthroses remains unclear, though defects in osteogenesis have been posited. Here, we applied time-series single-cell RNA-sequencing (scRNA-seq) to patient-matched control and pseudarthrosis-derived primary bone stromal cells (BSCs). We show that osteogenic specification to an osteoblast progenitor cell population was evident for control bone-derived cells and haploinsufficient pseudarthrosis-derived cells. Similar results were observed for somatic patient fracture-derived NF1-/- cells; however, expression of genetic pathways associated with skeletal mineralization were significantly reduced in NF1-/- cells compared with fracture-derived NF1+/- cells. In mice, we show that Nf1 expressed in bone marrow osteoprogenitors is required for the maintenance of the adult skeleton. Results from our study implicate impaired Clec11a-Itga11-Wnt signaling in the pathogenesis of NF1-associated skeletal disease. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

New insights into pathogenesis of congenital pseudarthrosis of tibia in children using periosteum proteomics analysis.

RATIONALE: The exact etiology and pathogenesis of congenital pseudarthrosis of tibia (CPT) are not clear. Quantitative proteomics analysis plays a vital role in disease pathology research. Tandem mass tag (TMT)-based proteomics techniques were employed to identify and analyze the differentially expressed proteins (DEP) in the tibia periosteum tissues of CPT patients. METHODS: The samples were divided into three groups: CPT with NF1 group, CPT without NF1 group (non-NF1-CPT), and control group (patients with open tibial fracture). A fold change ≥1.5 or ≤0.66 and P-value <0.05 were used as the thresholds to screen DEPs. Subsequently, bioinformatics resources such as online tools DAVID and String were used to generate gene ontology (GO) annotation, KEGG pathways enrichment, and protein-protein interaction (PPI) network for these DEPs. RESULTS: The results show that a total of 347 proteins were differentially expressed in NF1-CPT groups, 212 of which were upregulated and 135 were downregulated. There were more DEPs in non-NF1-CPT groups; we identified 467 DEPs, including 281 upregulated and 186 downregulated. Among them, NF1-CPT groups and non-NF1-CPT groups shared 231 DEPs, and the remaining 230 DEPs showed the same expression trend in the two disease groups, with 117 upregulated and 113 downregulated. In particular, 116 proteins were altered only in NF1-CPT groups (94 were upregulated and 22 were downregulated), whereas 236 proteins were altered only in non-NF1-CPT groups (164 were upregulated and 72 were downregulated). Finally, compared with non-NF1-CPT groups, 47 proteins changed 1.5-fold and P-value < 0.05 in NF1-CPT groups. CONCLUSIONS: To sum up, we found that common DEPS in periosteum of NF1-CPT and non-NF1-CPT groups are mainly involved in cell matrix assembly, cell adhesion, AKT-PI3K signal pathway activation, and vascular agglutination, which indicate that these are the pathological characteristics of CPT. The osteogenic ability is weak, the osteoclastic ability is strong, the vascular lumen is narrow, the invasive growth and the proliferation of fibroblasts are enhanced in CPT patients.

Case series of congenital pseudarthrosis of the tibia unfulfilling neurofibromatosis type 1 diagnosis: 21% with somatic NF1 haploinsufficiency in the periosteum.

Up to 84% of patients with congenital pseudarthrosis of the tibia (CPT) present with neurofibromatosis type 1 (NF1) (NF1-CPT). However, the etiology of CPT not fulfilling the NIH diagnostic criteria for NF1 (non-NF1-CPT) is not well understood. Here, we collected the periosteum tissue from the pseudarthrosis (PA) site of 43 non-NF1-CPT patients and six patients with NF1-CPT, together with the blood or oral specimen of trios (probands and unaffected parents). Whole-exome plus copy number variation sequencing, multiplex ligation-dependent probe amplification (MLPA), ultra-high amplicon sequencing, and Sanger sequencing were employed to identify pathogenic variants. The result showed that nine tissues of 43 non-NF1-CPT patients (21%) had somatic mono-allelic NF1 inactivation, and five of six NF1-CPT patients (83.3%) had bi-allelic NF1 inactivation in tissues. However, previous literature involving genetic testing did not reveal somatic mosaicism in non-NF1-CPT patients so far. In NF1-CPT patients, when the results from earlier reports and the present study were combined, 66.7% of them showed somatic NF1 inactivation in PA tissues other than germline inactivation. Furthermore, no diagnostic variants from other known genes (GNAS, AKT1, PDGFRB, and NOTCH3) related to skeletal dysplasia were identified in the nine NF1 positive non-NF1-CPT patients and six NF1-CPT patients. In conclusion, we detected evident somatic mono-allelic NF1 inactivation in the non-NF1-CPT. Thus, for pediatric patients without NF1 diagnosis, somatic mutations in NF1 are important.

Congenital Pseudarthrosis of the Tibia Associated With Cleidocranial Dysostosis: Case Report and Literature Review.

CASE: We describe a case of 2 individually rare diseases existing comorbidly in the form of congenital pseudarthrosis of the tibia (CPT) coincident with cleidocranial dysostosis and provide a review of the literature, including the sole preexisting documented coincidence. CONCLUSION: Understanding, treatment, and surgical protocol of CPT have changed considerably since this comorbidity was last reported. Updates include synostosis, periosteal grafting, the use of bone morphogenetic protein, and bisphosphonates. Our case varies from the previous in associated disorder and family history. The relationship between CBFA1 and RUNX2 genes may hold the key, but further study is needed.

Identification and characterization of NF1 and non-NF1 congenital pseudarthrosis of the tibia based on germline NF1 variants: genetic and clinical analysis of 75 patients.

BACKGROUND: Congenital pseudarthrosis of the tibia (CPT) is a rare disease. Some patients present neurofibromatosis type 1 (NF1), while some others do not manifest NF1 (non-NF1). The etiology of CPT, particularly non-NF1 CPT, is not well understood. Here we screened germline variants of 75 CPT cases, including 55 NF1 and 20 non-NF1. Clinical data were classified and analyzed based on NF1 gene variations to investigate the genotype-phenotype relations of the two types of patients. RESULTS: Using whole-exome sequencing and Multiplex Ligation-Dependent Probe Amplification, 44 out of 55 NF1 CPT patients (80.0%) were identified as carrying pathogenic variants of the NF1 gene. Twenty-five variants were novel; 53.5% of variants were de novo, and a higher proportion of their carriers presented bone fractures compared to inherited variant carriers. No NF1 pathogenic variants were found in all 20 non-NF1 patients. Clinical features comparing NF1 CPT to non-NF1 CPT did not show significant differences in bowing or fracture onset, lateralization, tissue pathogenical results, abnormality of the proximal tibial epiphysis, and follow-up tibial union after surgery. A considerably higher proportion of non-NF1 patients have cystic lesion (Crawford type III) and used braces after surgery. CONCLUSIONS: We analyzed a large cohort of non-NF1 and NF1 CPT patients and provided a new perspective for genotype-phenotype features related to germline NF1 variants. Non-NF1 CPT in general had similar clinical features of the tibia as NF1 CPT. Germline NF1 pathogenic variants could differentiate NF1 from non-NF1 CPT but could not explain the CPT heterogeneity of NF1 patients. Our results suggested that non-NF1 CPT was probably not caused by germline NF1 pathogenic variants. In addition to NF1, other genetic variants could also contribute to CPT pathogenesis. Our findings would facilitate the interpretation of NF1 pathogenic variants in CPT genetic counseling.

Improved union and bone strength in a mouse model of NF1 pseudarthrosis treated with recombinant human bone morphogenetic protein-2 and zoledronic acid.

Tibial pseudarthrosis associated with Neurofibromatosis type 1 (NF1) is an orthopedic condition with consistently poor clinical outcomes. Using a murine model that features localized double inactivation of the Nf1 gene in an experimental tibial fracture, we tested the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) and/or the bisphosphonate zoledronic acid (ZA). Tibiae were harvested at 3 weeks for analysis, at which time there was negligible healing in un-treated control fractures (7% union). In contrast, rhBMP-2 and rhBMP-2/ZA groups showed significantly greater union (87% and 93%, p < 0.01 for both). Treatment with rhBMP-2 led to a 12-fold increase in callus bone volume and this was further increased in the rhBMP-2/ZA group. Mechanical testing of the healed rhBMP-2 and rhBMP-2/ZA fractures showed that the latter group had significantly higher mechanical strength and was restored to that of the un-fractured contralateral leg. Co-treatment with rhBMP-2/ZA also reduced fibrous tissue infiltration at the fracture site compared to rhBMP alone (p = 0.068). These data support the future clinical investigation of this combination of anabolic and anti-resorptive agents for the treatment of NF1 pseudarthrosis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:930-936, 2018.

Utilization of Whole-Exome Next-Generation Sequencing Variant Read Frequency for Detection of Lesion-Specific, Somatic Loss of Heterozygosity in a Neurofibromatosis Type 1 Cohort with Tibial Pseudarthrosis.

A subset of neurofibromatosis type 1 patients develop tibial dysplasia, which can lead to pseudarthrosis. The tissue from the tibial pseudarthrosis region commonly has a somatic second hit in NF1: single-nucleotide variants, small deletions, or loss of heterozygosity (LOH). We used exome next-generation sequencing (NGS) variant frequency data (allelic imbalance analysis) to detect somatic LOH in pseudarthrosis tissue from three individuals with clinically and diagnostically confirmed neurofibromatosis type 1, and verified the results with microarray. The variant files were parsed and plotted using python scripts, and the NGS variant frequencies between the affected tissue and blood sample were compared. Individuals without somatic single-nucleotide variants or small insertions/deletions were tested for somatic LOH using the NGS variant allele frequencies. One individual's NGS data indicated no LOH in chromosome 17. The other two individuals demonstrated somatic LOH inclusive of NF1: one had an LOH region of approximately one million bases and Contra (NGS copy number program) indicated a somatic deletion and the other individual had LOH for most of chromosome 17q and Contra indicated no copy number change (microarray data verified this sample as copy neutral somatic LOH). Both LOH and copy number variation detected by NGS data correlated with microarray data, demonstrating the somatic LOH second hit can be detected directly from the NGS data.

Novel phenotypes of NF1 patients from unrelated Chinese families with tibial pseudarthrosis and anemia.

Neurofibromatosis type 1 (NF1) is an autosomal dominant, multi-system, neurocutaneous disorder, manifested with neurofibromas and Cafe´-au-lait spots. Germline mutations in NF1 gene are associated with Neurofibromatosis type 1. NF1 gene encodes neurofibromin, a RAS-specific GTPase activating protein. In our study, we present a clinical molecular study of four Chinese probands with NF1 from four unrelated families, showing extreme phenotypic variation with rare phenotype. In family 1, the proband is a 16 months old girl with multiple café-au-lait spots throughout her whole body. In family 2, the proband is a 6 months old girl with several café-au-lait spots mostly in her trunk and in lower limbs. In family 3, the proband is a 4 months old boy with several café-au-lait spots, tibial pseudarthrosis, and chronic iron deficiency anemia. In family 4, the proband is a 14 years old boy with multiple café-au-lait spots of variable sizes. Targeted exome capture based next generation sequencing and Sanger sequencing identified a novel mutation and three previously reported mutations in these four probands. These four mutations in NF1 gene were causing disease phenotypes in these four probands and was absent in unaffected family members and in healthy controls. According to the variant interpretation guideline of American College of Medical Genetics and Genomics (ACMG), these four mutations, are classified as "likely pathogenic". Our result expands the mutational spectrum of the NF1 gene associated with neurofibromatosis type1.

Capturing the wide variety of impaired fracture healing phenotypes in Neurofibromatosis Type 1 with eight key factors: a computational study.

Congenital pseudarthrosis of the tibia (CPT) is a rare disease which normally presents itself during early childhood by anterolateral bowing of the tibia and spontaneous tibial fractures. Although the exact etiology of CPT is highly debated, 40-80% of CPT patients are carriers of a mutation in the Neurofibromatosis Type 1 (NF1) gene, which can potentially result in an altered phenotype of the skeletal cells and impaired bone healing. In this study we use a computational model of bone regeneration to examine the effect of the Nf1 mutation on bone fracture healing by altering the parameter values of eight key factors which describe the aberrant cellular behaviour of Nf1 haploinsufficient and Nf1 bi-allelically inactivated cells. We show that the computational model is able to predict the formation of a hamartoma as well as a wide variety of CPT phenotypes through different combinations of altered parameter values. A sensitivity analysis by "Design of Experiments" identified the impaired endochondral ossification process and increased infiltration of fibroblastic cells as key contributors to the degree of severity of CPT. Hence, the computational model results have added credibility to the experimental hypothesis of a genetic cause (i.e. Nf1 mutation) for CPT.

Evaluation of somatic mutations in tibial pseudarthrosis samples in neurofibromatosis type 1.

BACKGROUND: Tibial pseudarthrosis is associated with neurofibromatosis type 1 (NF1) and there is wide clinical variability of the tibial dysplasia in NF1, suggesting the possibility of genetic modifiers. Double inactivation of NF1 is postulated to be necessary for the development of tibial pseudarthrosis, but tissue or cell of origin of the 'second hit' mutation remains unclear. METHODS: Exome sequencing of different sections of surgically resected NF1 tibial pseudarthrosis tissue was performed and compared to germline (peripheral blood). RESULTS: A germline NF1 splice site mutation (c.61-2A>T, p.L21 M68del) was identified from DNA extracted from peripheral blood. Exome sequencing of DNA extracted from tissue removed during surgery of the tibial pseudarthrosis showed a somatic mutation of NF1 (c.3574G>T, p.E1192*) in the normal germline allele. Further analysis of different regions of the tibial pseudarthrosis sample showed enrichment of the somatic mutation in the soft tissue within the pseudarthrosis site and absence of the somatic mutation in cortical bone. In addition, a germline variant in PTPN11 (c.1658C>T, p.T553M), a gene involved in the RAS signal transduction pathway was identified, although the clinical significance is unknown. CONCLUSIONS: Given that the NF1 somatic mutation was primarily detected in the proliferative soft tissue at the pseudarthrosis site, it is likely that the second hit occurred in mesenchymal progenitors from the periosteum. These results are consistent with a defect of differentiation, which may explain why the mutation is found in proliferative cells and not within cortical bone tissue, as the latter by definition contains mostly mature differentiated osteoblasts and osteocytes.

Combined MEK inhibition and BMP2 treatment promotes osteoblast differentiation and bone healing in Nf1Osx -/- mice.

Neurofibromatosis type I (NF1) is an autosomal dominant disease with an incidence of 1/3000, caused by mutations in the NF1 gene, which encodes the RAS/GTPase-activating protein neurofibromin. Non-bone union after fracture (pseudarthrosis) in children with NF1 remains a challenging orthopedic condition to treat. Recent progress in understanding the biology of neurofibromin suggested that NF1 pseudarthrosis stems primarily from defects in the bone mesenchymal lineage and hypersensitivity of hematopoietic cells to TGFß. However, clinically relevant pharmacological approaches to augment bone union in these patients remain limited. In this study, we report the generation of a novel conditional mutant mouse line used to model NF1 pseudoarthrosis, in which Nf1 can be ablated in an inducible fashion in osteoprogenitors of postnatal mice, thus circumventing the dwarfism associated with previous mouse models where Nf1 is ablated in embryonic mesenchymal cell lineages. An ex vivo-based cell culture approach based on the use of Nf1(flox/flox) bone marrow stromal cells showed that loss of Nf1 impairs osteoprogenitor cell differentiation in a cell-autonomous manner, independent of developmental growth plate-derived or paracrine/hormonal influences. In addition, in vitro gene expression and differentiation assays indicated that chronic ERK activation in Nf1-deficient osteoprogenitors blunts the pro-osteogenic property of BMP2, based on the observation that only combination treatment with BMP2 and MEK inhibition promoted the differentiation of Nf1-deficient osteoprogenitors. The in vivo preclinical relevance of these findings was confirmed by the improved bone healing and callus strength observed in Nf1osx (-/-) mice receiving Trametinib (a MEK inhibitor) and BMP2 released locally at the fracture site via a novel nanoparticle and polyglycidol-based delivery method. Collectively, these results provide novel evidence for a cell-autonomous role of neurofibromin in osteoprogenitor cells and insights about a novel targeted approach for the treatment of NF1 pseudoarthrosis.

Neurofibromin deficiency-associated transcriptional dysregulation suggests a novel therapy for tibial pseudoarthrosis in NF1.

Neurofibromatosis type 1 (NF1) is an autosomal dominant disease caused by mutations in NF1. Among the earliest manifestations is tibial pseudoarthrosis and persistent nonunion after fracture. To further understand the pathogenesis of pseudoarthrosis and the underlying bone remodeling defect, pseudoarthrosis tissue and cells cultured from surgically resected pseudoarthrosis tissue from NF1 individuals were analyzed using whole-exome and whole-transcriptome sequencing as well as genomewide microarray analysis. Genomewide analysis identified multiple genetic mechanisms resulting in somatic biallelic NF1 inactivation; no other genes with recurring somatic mutations were identified. Gene expression profiling identified dysregulated pathways associated with neurofibromin deficiency, including phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling pathways. Unlike aggressive NF1-associated malignancies, tibial pseudoarthrosis tissue does not harbor a high frequency of somatic mutations in oncogenes or other tumor-suppressor genes, such as p53. However, gene expression profiling indicates that pseudoarthrosis tissue has a tumor-promoting transcriptional pattern, despite lacking tumorigenic somatic mutations. Significant overexpression of specific cancer-associated genes in pseudoarthrosis highlights a potential for receptor tyrosine kinase inhibitors to target neurofibromin-deficient pseudoarthrosis and promote proper bone remodeling and fracture healing.

Hyperactive Ras/MAPK signaling is critical for tibial nonunion fracture in neurofibromin-deficient mice.

Neurofibromatosis type 1 (NF1) is a common genetic disorder affecting 1 in 3500 individuals. Patients with NF1 are predisposed to debilitating skeletal manifestations, including osteopenia/osteoporosis and long bone pseudarthrosis (nonunion fracture). Hyperactivation of the Ras/mitogen-activated protein kinase (MAPK) pathway in NF1 is known to underlie aberrant proliferation and differentiation in cell lineages, including osteoclast progenitors and mesenchymal stem cells (MSCs) also known as osteoblast progenitors (pro-OBLs). Our current study demonstrates the hyper Ras/MAPK as a critical pathway underlying the pathogenesis of NF1-associated fracture repair deficits. Nf1-deficient pro-OBLs exhibit Ras/MAPK hyperactivation. Introduction of the NF1 GTPase activating-related domain (NF1 GAP-related domain) in vitro is sufficient to rescue hyper Ras activity and enhance osteoblast (OBL) differentiation in Nf1(-/-) pro-OBLs and NF1 human (h) MSCs cultured from NF1 patients with skeletal abnormalities, including pseudarthrosis or scoliosis. Pharmacologic inhibition of mitogen-activated protein kinase kinase (MEK) signaling with PD98059 partially rescues aberrant Erk activation while enhancing OBL differentiation and expression of OBL markers, osterix and osteocalcin, in Nf1-deficient murine pro-OBLs. Similarly, MEK inhibition enhances OBL differentiation of hMSCs. In addition, PD98059 rescues aberrant osteoclast maturation in Nf1 haploinsufficient bone marrow mononuclear cells (BMMNCs). Importantly, MEK inhibitor significantly improves fracture healing in an NF1 murine model, Col2.3Cre;Nf1(flox/-). Collectively, these data indicate the Ras/MAPK cascade as a critical pathway in the pathogenesis of bone loss and pseudarthrosis related to NF1 mutations. These studies provide evidence for targeting the MAPK pathway to improve bone mass and treat pseudarthrosis in NF1.

Is double inactivation of the Nf1 gene responsible for the development of congenital pseudarthrosis of the tibia associated with NF1?

The pathogenic mechanism responsible for congenital pseudarthrosis of the tibia (CPT) is not well understood although the possibility of double inactivation of the neurofibromatosis type 1 (Nf1) gene has been suggested. In the present study, loss of heterozygosity was investigated in fibrous hamartoma tissues harvested from 16 patients with CPT associated with NF1 using four genetic markers that span the Nf1 gene. Based on the assumption that a single cell with double inactivation of Nf1 would undergo clonal growth and cause fibrous hamartoma, we investigated clonality in fibrous hamartoma tissues by analyzing X-chromosome inactivation patterns in 11 female patients. Loss of Nf1 heterozygosity in fibrous hamartoma tissues was observed at one or two genetic markers in 4 out of the 16 patients tested. In clonality assays, 3 of 11 patients showed a clonal growth pattern, 5 a non-clonal pattern, and 3 were non-informative. These findings support that double inactivation of the Nf1 gene and subsequent clonal growth could be a pathogenic feature of the fibrous hamartoma tissue at least in some of the CPT but might not be essential requirements of CPT development.

[Orthopaedic manifestations of Von Recklinghausen's neurofibromatosis]. / Manifestations orthopédiques de la neurofibromatose de Von Recklinghausen.

OBJECTIVE: Von Recklinghausen's neurofibromatosis is a dominant autosomic genetic disease characterized by different clinical manifestations. The goal of this work was to study its orthopaedic manifestations and to show the characteristics of their management. METHOD: A retrospective study was carried out on 15 patients having a Von Recklinghausen's neurofibromatosis. For each patient, different orthopaedic manifestations and their evolution after treatment were analyzed. These manifestations were classified in spinal deformities, pseudarthrosis of long bones and tumours of the peripheral nerves. RESULTS: The spinal deformities were observed in 9 cases. A dystrophic scoliosis was observed in 6 patients with an average angle of 50° and was associated to a kyphosis in 5 patients. The treatment was surgical by posterior arthrodesis in 2 cases and circumferential arthrodesis in 2 cases. The congenital curves and pseudarthroses of leg were observed in 5 cases, localized at the lower third of the leg in all cases. An Ilizarov external fixator with segmental osseous transport was carried out in 2 patients. The duration of the external fixator was 23 months ½ with 5 interventions in each case. Four plexiform neurofibromas and 3 nodular neurofibromas were observed. A transformation into neurofibrosarcoma was found in 2 patients. In one case, a resection without functional sacrifice was carried out and in the other case the patient was dead before the resection. CONCLUSION: The orthopaedic manifestations of Von Recklinghausen's neurofibromatosis are frequent, varied and have a difficult management. The functional and sometimes vital prognoses are challenging.

Coexistence of neurofibromatosis type 1 and mosaic trisomy 8 in the same patient.

We described trisomy 8 mosaicism in a 6-month-old boy with left corneal leukoma, strabismus, posterior urethral valve, tibial bowing and congenital pseudarthrosis of the tibia (CPT) on graphic of left tibia. The patient also had some minor anomalies such as short philtrum, full everted lower lip, microretrognathia, flexion contracture on his left thumb, deep palmar and plantar creases and three cafe-au-lait macules (CALM) larger than 1 cm on the abdomen. Peripheral blood karyotype analysis of the patient showed 46,XY(10%)/47,XY,+8 (90%)). Mosaic trisomy 8 is a rare syndrome characterized by renal, cardiac, ophthalmologic anomalies, dysmorphic facial features and some skeletal manifestations. When re-evaluated at 2 years of age, his gross motor development was delayed and he also had 12 CALM larger than 1 cm, hence the patient fulfilled NIH diagnostic criteria for Neurofibromatosis type 1 (NF 1) based on the CALM and CPT. A truncating mutation was found through comprehensive NF1 mutation analysis, i.e., c.1019_1020delCT (p.Ser340CysfsX12). Here we report a patient with both mosaic trisomy 8 and NF1, which was not described previously.

Orthopaedic manifestations of neurofibromatosis type 1.

Neurofibromatosis type 1 (NF-1) is an autosomal dominant disease that affects 1 in 3,000 persons worldwide. Café-au-lait macules and peripheral nerve sheath tumors (ie, neurofibromas) are the most commonly recognized manifestations of NF-1. However, NF-1 affects multiple organ systems, and a multidisciplinary approach to treatment is required. Management of the orthopaedic manifestations of NF-1 is often difficult. The most complex manifestations are scoliosis (dystrophic and nondystrophic), congenital pseudarthrosis of the tibia, and problems related to soft-tissue tumors. Metabolic bone disease is common; many patients are frankly osteopenic, which further complicates treatment. Dystrophic scoliosis, which may be caused by either bony dysplasia or intraspinal pathology, is characterized by early presentation and rapid progression. Pseudarthrosis is common even after instrumented fusion. Nondystrophic scoliosis tends to behave like adolescent idiopathic scoliosis, although it may present earlier and is associated with a higher rate of pseudarthrosis. Congenital pseudarthrosis of the tibia is a long-bone dysplasia that afflicts patients with NF-1. Management of this osseous deformity is challenging. Failure to achieve union and refracture are common.

Clavicular pseudoarthrosis, anomalous coronary artery and extra crease of the fifth finger-previously unreported features in individuals with class II 1q21.1 microdeletions.

Submicroscopic deletions of two adjacent regions within chromosomal band 1q21.1 were recently associated with two distinct phenotypes: A deleted region of 200-500 kb was found in individuals with Thrombocytopenia Absent Radius syndrome (TAR). Deletion in another region of about 1.25 Mb that is located just telomeric of the TAR region, referred to as distal 1q21.1 region, was found to be associated with a phenotype of cognitive impairment, congenital heart defects and other variable manifestations. A significant proportion of individuals with either of the two deletions did not have phenotypic abnormalities. More than 40 individuals with distal 1q21.1 deletions have been reported to-date. A proportion of them (9 reported individuals) had larger (>2 Mb) deletions involving both the TAR and the distal 1q21.1 regions, referred to as class II deletions. We describe here four additional individuals from two families with such class II deletions, who presented with previously unreported manifestations: clavicular pseudoarthrosis and anomalous origin of the coronary artery in the proband of the first family; an extra transverse crease of the fifth finger, segregating in two of the three deletion carriers in the second family. Previously reported features, associated with such microdeletions - absolute or relative microcephaly, cognitive impairment and short stature, were variably observed in the reported individuals. This report expands the phenotypic spectrum associated with class II 1q21.1 deletions, and demonstrates striking phenotypic variability even within the same family.

Familial pseudarthrosis of the clavicle: does it need treatment?

The eighth family with multiple cases of congenital pseudarthrosis of the clavicle is described. This usually presents as a clavicular lump and is distinct from more common conditions such as birth fractures, craniocleidal dysostosis and neurofibromatosis. There has so far been no clear indication on whether familial pseudarthrosis of the clavicle should be treated operatively. We recommend that when a suspected case of congenital pseudarthrosis of the clavicle is diagnosed the parents and siblings be examined also. If other family members are affected, we advise that the treatment should be conservative.

Pseudoarthrosis of the clavicle and copper beaten skull associated with chromosome 10p11.21p12.1 microdeletion.

Congenital pseudoarthrosis of the clavicle (CPC) has been described in several genetic conditions including Floating-Harbor and Goltz syndromes, but rarely as a prompt to specific cytogenetic abnormalities. We report on a case of a de novo 10p11.21p12.1 microdeletion in a boy with multiple problems including a beaten copper appearance of the cranium on skull X-ray and pseudoarthrosis of the right clavicle. This is the first description of these particular skeletal findings in the context of a chromosome 10p deletion.