Achondroplasia

A novel non-invasive detection method for the FGFR3 gene mutation in maternal plasma for a fetal achondroplasia diagnosis based on signal amplification by hemin-MOFs/PtNPs

The small amount of cell-free fetal DNA (cffDNA) can be a useful biomarker for early non-invasive prenatal diagnosis (NIPD) of achondroplasia. In this study, a novel non-invasive electrochemical DNA sensor for ultrasensitive detecting FGFR3 mutation gene, a pathogenic gene of achondroplasia, based on biocatalytic signal materials and the biotin-streptavidin system are presented. Notably encapsulation of hemin in metal-organic frameworks-based materials (hemin-MOFs) and platinum nanoparticles (PtNPs) were used to prepare hemin-MOFs/PtNPs composites via a one-beaker-one-step reduction. We utilized hemin-MOFs/PtNPs for signal amplification because the promising hemin-MOFs/PtNPs nanomaterial has remarkable ability of catalyze H₂O₂ as well as excellent conductivity. To further amplify the electrochemical signal, reduced graphene oxide-tetraethylene pentamine (rGO-TEPA), gold nanoparticles and streptavidin were selected for modification of the electrode to enhance the conductivity and immobilize more biotin-modified capture probe (Bio-CP) through the high specificity and superior affinity between streptavidin and biotin. The electrochemical signal was primarily derived from the synergistic catalysis of H₂O₂ by hemin and PtNPs and recorded by Chronoamperometry. Under the optimal conditions, this newly designed biosensor exhibited sensitive detection of FGFR3 from 0.1fM to 1nM with a low detection limit of 0.033fM (S/N=3). We proposed that this ultrasensitive biosensor is useful for the early non-invasive prenatal diagnosis of achondroplasia.

The neuropsychological function of children with achondroplasia

The current observational study had three specific objectives: (i) to document any neuropsychological impairment in a sample of children with achondroplasia; (ii) to explore individual variability; and (iii) to determine the functional impact of any impairments. Fourteen children aged between 6 and 15 years with a medically confirmed diagnosis of achondroplasia (FGFR 3 mutation positive) underwent a comprehensive standardized neuropsychological evaluation. On average, while generally still within normal limits, significantly lower scores compared to standardized means were identified on: Full-scale IQ, verbal IQ, working memory, arithmetic, attention, executive functioning and aspects of day-to-day emotional, social, and behavioral functioning. Clinically significant levels of impairment at a group level were identified on measures of: arithmetic, attention, and executive functioning. There was variability among the group and for most measures scores ranged from impaired to within normal limits. A high percentage of children were impaired on measures of: verbal IQ, attention and executive functioning. Results of this study suggest a need for individual neuropsychological evaluation and monitoring of children with achondroplasia and suggest verbal IQ, arithmetic, attention, and executive functioning are particularly common areas of impairment. © 2016 Wiley Periodicals, Inc.

Pathogenic Cysteine Removal Mutations in FGFR Extracellular Domains Stabilize Receptor Dimers and Perturb the TM Dimer Structure

Missense mutations that introduce or remove cysteine residues in receptor tyrosine kinases are believed to cause pathologies by stabilizing the active receptor tyrosine kinase dimers. However, the magnitude of this stabilizing effect has not been measured for full-length receptors. Here, we characterize the dimer stabilities of three full-length fibroblast growth factor receptor (FGFR) mutants harboring pathogenic cysteine substitutions: the C178S FGFR1 mutant, the C342R FGFR2 mutant, and the C228R FGFR3 mutant. We find that the three mutations stabilize the FGFR dimers. We further see that the mutations alter the configuration of the FGFR transmembrane dimers. Thus, both aberrant dimerization and perturbed dimer structure likely contribute to the pathological phenotypes arising due to these mutations.

Skeleton Genetics: a comprehensive database for genes and mutations related to genetic skeletal disorders

Genetic skeletal disorders (GSD) involving the skeletal system arises through disturbances in the complex processes of skeletal development, growth and homeostasis and remain a diagnostic challenge because of their clinical heterogeneity and genetic variety. Over the past decades, tremendous effort platforms have been made to explore the complex heterogeneity, and massive new genes and mutations have been identified in different GSD, but the information supplied by literature is still limited and it is hard to meet the further needs of scientists and clinicians. In this study, combined with Nosology and Classification of genetic skeletal disorders, we developed the first comprehensive and annotated genetic skeletal disorders database, named 'SkeletonGenetics', which contains information about all GSD-related knowledge including 8225 mutations in 357 genes, with detailed information associated with 481 clinical diseases (2260 clinical phenotype) classified in 42 groups defined by molecular, biochemical and/or radiographic criteria from 1698 publications. Further annotations were performed to each entry including Gene Ontology, pathways analysis, protein-protein interaction, mutation annotations, disease-disease clustering and gene-disease networking. Furthermore, using concise search methods, intuitive graphical displays, convenient browsing functions and constantly updatable features, 'SkeletonGenetics' could serve as a central and integrative database for unveiling the genetic and pathways pre-dispositions of GSD.Database URL: http://101.200.211.232/skeletongenetics/.

Paleodysmorphology and paleoteratology: Diagnosing and interpreting congenital conditions of the skeleton in anthropological contexts

Most congenital conditions have low prevalence, but collectively they occur in a few percent of all live births. Congenital conditions are rarely encountered in anthropological studies, not least because many of them have no obvious effect on the skeleton. Here, we discuss two groups of congenital conditions that specifically affect the skeleton, either qualitatively or quantitatively. Skeletal dysplasias (osteochondrodysplasias) interfere with the histological formation, growth and maturation of skeletal tissues leading to diminished postural length, but the building plan of the body is unaffected. Well- known skeletal dysplasias represented in the archeological record include osteogenesis imperfecta and achondroplasia. Dysostoses, in contrast, interfere with the building plan of the body, leading to e.g. missing or extraskeletal elements, but the histology of the skeletal tissues is unaffected. Dysostoses can concern the extremities (e.g., oligodactyly and polydactyly), the vertebral column (e.g., homeotic and meristic anomalies), or the craniofacial region. Conditions pertaining to the cranial sutures, i.e., craniosynostoses, can be either skeletal dysplasias or dysostoses. Congenital conditions that are not harmful to the individual are known as anatomical variations, several of which have a high and population-specific prevalence that could potentially make them useful for determining ethnic origins. In individual cases, specific congenital conditions could be determinative in establishing identity, provided that ante-mortem registration of those conditions was ensured. Clin. Anat. 29:878-891, 2016. © 2016 The Authors Clinical Anatomy published by Wiley Periodicals, Inc. on behalf of American Association of Clinical Anatomists.

Effect of the achondroplasia mutation on FGFR3 dimerization and FGFR3 structural response to fgf1 and fgf2: A quantitative FRET study in osmotically derived plasma membrane vesicles

The G380R mutation in the transmembrane domain of FGFR3 is a germline mutation responsible for most cases of Achondroplasia, a common form of human dwarfism. Here we use quantitative Fӧster Resonance Energy Transfer (FRET) and osmotically derived plasma membrane vesicles to study the effect of the achondroplasia mutation on the early stages of FGFR3 signaling in response to the ligands fgf1 and fgf2. Using a methodology that allows us to capture structural changes on the cytoplasmic side of the membrane in response to ligand binding to the extracellular domain of FGFR3, we observe no measurable effects of the G380R mutation on FGFR3 ligand-bound dimer configurations. Instead, the most notable effect of the achondroplasia mutation is increased propensity for FGFR3 dimerization in the absence of ligand. This work reveals new information about the molecular events that underlie the achondroplasia phenotype, and highlights differences in FGFR3 activation due to different single amino-acid pathogenic mutations.

Molecular Physiology of Membrane Guanylyl Cyclase Receptors

cGMP controls many cellular functions ranging from growth, viability, and differentiation to contractility, secretion, and ion transport. The mammalian genome encodes seven transmembrane guanylyl cyclases (GCs), GC-A to GC-G, which mainly modulate submembrane cGMP microdomains. These GCs share a unique topology comprising an extracellular domain, a short transmembrane region, and an intracellular COOH-terminal catalytic (cGMP synthesizing) region. GC-A mediates the endocrine effects of atrial and B-type natriuretic peptides regulating arterial blood pressure/volume and energy balance. GC-B is activated by C-type natriuretic peptide, stimulating endochondral ossification in autocrine way. GC-C mediates the paracrine effects of guanylins on intestinal ion transport and epithelial turnover. GC-E and GC-F are expressed in photoreceptor cells of the retina, and their activation by intracellular Ca(2+)-regulated proteins is essential for vision. Finally, in the rodent system two olfactorial GCs, GC-D and GC-G, are activated by low concentrations of CO2and by peptidergic (guanylins) and nonpeptidergic odorants as well as by coolness, which has implications for social behaviors. In the past years advances in human and mouse genetics as well as the development of sensitive biosensors monitoring the spatiotemporal dynamics of cGMP in living cells have provided novel relevant information about this receptor family. This increased our understanding of the mechanisms of signal transduction, regulation, and (dys)function of the membrane GCs, clarified their relevance for genetic and acquired diseases and, importantly, has revealed novel targets for therapies. The present review aims to illustrate these different features of membrane GCs and the main open questions in this field.

Meckel's and condylar cartilages anomalies in achondroplasia result in defective development and growth of the mandible

Activating FGFR3 mutations in human result in achondroplasia (ACH), the most frequent form of dwarfism, where cartilages are severely disturbed causing long bones, cranial base and vertebrae defects. Because mandibular development and growth rely on cartilages that guide or directly participate to the ossification process, we investigated the impact of FGFR3 mutations on mandibular shape, size and position. By using CT scan imaging of ACH children and by analyzing Fgfr3^Y367C/+ mice, a model of ACH, we show that FGFR3 gain-of-function mutations lead to structural anomalies of primary (Meckel’s) and secondary (condylar) cartilages of the mandible, resulting in mandibular hypoplasia and dysmorphogenesis. These defects are likely related to a defective chondrocyte proliferation and differentiation and pan-FGFR tyrosine kinase inhibitor NVP-BGJ398 corrects Meckel’s and condylar cartilages defects ex vivo. Moreover, we show that low dose of NVP-BGJ398 improves in vivo condyle growth and corrects dysmorphologies in Fgfr3^Y367C/+ mice, suggesting that postnatal treatment with NVP-BGJ398 mice might offer a new therapeutic strategy to improve mandible anomalies in ACH and others FGFR3-related disorders.

Achondroplasia: Really rhizomelic?

Achondroplasia is the most common form of short limb dwarfism in humans. The shortening of the limb lengths in achondroplasia is widely described as "rhizomelic." While this appearance may be convincing clinically, the description is not necessarily true or helpful radiologically. The aims of this study, were therefore, to determine whether rhizomelic shortening is a true feature of achondroplasia at diagnosis in infancy. Humeral, radial, femoral, and tibial diaphyseal lengths were recorded by two independent observers from 22 skeletal surveys of infants with achondroplasia and compared with 150 normal age-matched control subjects. Upper and lower limb bone length ratios (radial/humeral and tibial/femoral lengths, respectively) in both groups were compared using an unpaired t-test. Mean upper limb length ratios were statistically higher within the achondroplasia group at 0.87 ± 0.04 (n = 22, mean age 70 ± 94 days) compared to normal controls at 0.79 ± 0.02 (n = 150, mean age 113 days ± 88 days; P < 0.0001). Lower limb length ratios were not significantly different between groups (0.84 ± 0.04 vs. 0.83 ± 0.02, P = 0.46). There was good inter-observer agreement of limb length measurements, with an average measurement difference of 0.1 ± 1.4 mm. In conclusion, infants with achondroplasia demonstrate statistically significant rhizomelic shortening within the upper limbs, but not lower limbs at diagnosis, compared to normal controls. The term "rhizomelic shortening" in relation to achondroplasia should be reserved when describing upper limb proportions. © 2016 Wiley Periodicals, Inc.

Serum NT-proCNP levels increased after initiation of GH treatment in patients with achondroplasia/hypochondroplasia

OBJECTIVE

Serum amino-terminal propeptide of C-type natriuretic peptide (NT-proCNP) levels have been proposed as a biomarker of linear growth in healthy children. The usefulness of NT-proCNP in patients with achondroplasia (ACH)/hypochondroplasia (HCH) remains to be elucidated. The objective was to study whether serum NT-proCNP level is a good biomarker for growth in ACH/HCH and other patients of short stature.

DESIGN

This was a longitudinal cohort study.

PATIENTS

Sixteen children with ACH (aged 0·4-4·3 years), six children with HCH (2·7-6·3 years), 23 children with idiopathic short stature (ISS) (2·2-9·0 years), eight short children with GH deficiency (GHD) (2·9-6·8 years) and five short children born small for gestational age (SGA) (2·0-6·6 years). Patients with ACH/HCH received GH treatment for 1 year.

MEASUREMENTS

Serum NT-proCNP levels and height were measured.

RESULTS

NT-proCNP levels positively correlated with height velocity in these short children (P < 0·05, r = 0·27). NT-proCNP levels inversely correlated with age in children with ISS alone (P < 0·01, r = -0·55). Serum NT-proCNP levels in patients with ACH/HCH were increased 3 months following the initiation of GH treatment (P < 0·05). Height SDS gain during GH treatment for 1 year was positively correlated with the changes in NT-proCNP levels after the initiation of GH (P < 0·01, r = 0·72).

CONCLUSION

Serum NT-proCNP levels may be a good biomarker to indicate the effect of GH treatment on growth in patients with ACH/HCH at least in the first year and height velocity in short stature patients.

Tyrosine kinase inhibitor NVP-BGJ398 functionally improves FGFR3-related dwarfism in mouse model

Achondroplasia (ACH) is the most frequent form of dwarfism and is caused by gain-of-function mutations in the fibroblast growth factor receptor 3-encoding (FGFR3-encoding) gene. Although potential therapeutic strategies for ACH, which aim to reduce excessive FGFR3 activation, have emerged over many years, the use of tyrosine kinase inhibitor (TKI) to counteract FGFR3 hyperactivity has yet to be evaluated. Here, we have reported that the pan-FGFR TKI, NVP-BGJ398, reduces FGFR3 phosphorylation and corrects the abnormal femoral growth plate and calvaria in organ cultures from embryos of the Fgfr3Y367C/+ mouse model of ACH. Moreover, we demonstrated that a low dose of NVP-BGJ398, injected subcutaneously, was able to penetrate into the growth plate of Fgfr3Y367C/+ mice and modify its organization. Improvements to the axial and appendicular skeletons were noticeable after 10 days of treatment and were more extensive after 15 days of treatment that started from postnatal day 1. Low-dose NVP-BGJ398 treatment reduced intervertebral disc defects of lumbar vertebrae, loss of synchondroses, and foramen-magnum shape anomalies. NVP-BGJ398 inhibited FGFR3 downstream signaling pathways, including MAPK, SOX9, STAT1, and PLCγ, in the growth plates of Fgfr3Y367C/+ mice and in cultured chondrocyte models of ACH. Together, our data demonstrate that NVP-BGJ398 corrects pathological hallmarks of ACH and support TKIs as a potential therapeutic approach for ACH.

Functional characteristics of mesenchymal stem cells derived from the adipose tissue of a patient with achondroplasia

Mesenchymal stem cells (MSCs) can be isolated from various tissues including bone marrow, adipose tissue, skin dermis, and umbilical Wharton's jelly as well as injured tissues. MSCs possess the capacity for self-renewal and the potential for differentiation into adipogenic, osteogenic, and chondrogenic lineages. However, the characteristics of MSCs in injured tissues, such as achondroplasia (ACH), are not well known. In this study, we isolated MSCs from human subcutaneous adipose (ACH-SAMSCs) tissue and circumjacent human adipose tissue of the cartilage (ACH-CAMSCs) from a patient with ACH. We then analyzed the characterization of ACH-SAMSCs and ACH-CAMSCs, compared with normal human dermis-derived MSCs (hDMSCs). In flow cytometry analysis, the isolated ACH-MSCs expressed low levels of CD73, CD90, and CD105, compared with hDMSCs. Moreover, both ACH- SAMSCs and ACH-CAMSCs had constitutionally overactive fibroblast growth factor receptor 3 (FGFR3) and exhibited significantly reduced osteogenic differentiation, compared to enhanced adipogenic differentiation. The activity of extracellular signal-regulated kinases 1/2 (ERK1/2) and p38 mitogen-activated protein kinases (p38 MAPK) was increased in ACH-MSCs. In addition, the efficacy of osteogenic differentiation was slightly restored in osteogenic differentiation medium with MAPKs inhibitors. These results suggest that they play essential roles in MSC differentiation toward adipogenesis in ACH pathology. In conclusion, the identification of the characteristics of ACH-MSCs and the favoring of adipogenic differentiation via the FGFR3/MAPK axis might help to elucidate the pathogenic mechanisms relevant to other skeletal diseases and could provide targets for therapeutic interventions.

Droplet digital PCR combined with minisequencing, a new approach to analyze fetal DNA from maternal blood: application to the non-invasive prenatal diagnosis of achondroplasia

BACKGROUND

Achondroplasia is generally detected by abnormal prenatal ultrasound findings in the third trimester of pregnancy and then confirmed by molecular genetic testing of fetal genomic DNA obtained by aspiration of amniotic fluid. This invasive procedure presents a small but significant risk for both the fetus and mother. Therefore, non-invasive procedures using cell-free fetal DNA in maternal plasma have been developed for the detection of the fetal achondroplasia mutations.

METHODS

To determine whether the fetus carries the de novo mis-sense genetic mutation at nucleotide 1138 in FGFR3 gene involved in >99% of achondroplasia cases, we developed two independent methods: digital-droplet PCR combined with minisequencing, which are very sensitive methods allowing detection of rare alleles.

RESULTS

We collected 26 plasmatic samples from women carrying fetus at risk of achondroplasia and diagnosed to date a total of five affected fetuses in maternal blood. The sensitivity and specificity of our test are respectively 100% [95% confidence interval, 56.6-100%] and 100% [95% confidence interval, 84.5-100%].

CONCLUSIONS

This novel, original strategy for non-invasive prenatal diagnosis of achondroplasia is suitable for implementation in routine clinical testing and allows considering extending the applications of these technologies in non-invasive prenatal diagnosis of many other monogenic diseases. © 2016 John Wiley & Sons, Ltd.

FGF signaling in the osteoprogenitor lineage non-autonomously regulates postnatal chondrocyte proliferation and skeletal growth

Fibroblast growth factor (FGF) signaling is important for skeletal development; however, cell-specific functions, redundancy and feedback mechanisms regulating bone growth are poorly understood. FGF receptors 1 and 2 (Fgfr1 and Fgfr2) are both expressed in the osteoprogenitor lineage. Double conditional knockout mice, in which both receptors were inactivated using an osteoprogenitor-specific Cre driver, appeared normal at birth; however, these mice showed severe postnatal growth defects that include an ∼50% reduction in body weight and bone mass, and impaired longitudinal bone growth. Histological analysis showed reduced cortical and trabecular bone, suggesting cell-autonomous functions of FGF signaling during postnatal bone formation. Surprisingly, the double conditional knockout mice also showed growth plate defects and an arrest in chondrocyte proliferation. We provide genetic evidence of a non-cell-autonomous feedback pathway regulating Fgf9, Fgf18 and Pthlh expression, which led to increased expression and signaling of Fgfr3 in growth plate chondrocytes and suppression of chondrocyte proliferation. These observations show that FGF signaling in the osteoprogenitor lineage is obligately coupled to chondrocyte proliferation and the regulation of longitudinal bone growth.

Concomitant achondroplasia and developmental dysplasia of the hip

Achondroplasia (ACH) is the most common form of hereditary dwarfism and presents with multiple musculoskeletal anomalies but is not normally associated with premature hip arthritis. Developmental dysplasia of the hip (DDH) is a spectrum of disease resulting in shallow acetabular depth and a propensity for chronic femoral subluxation or dislocation; it is among the most common causes of premature arthritis. This case report describes the diagnosis of symptomatic DDH in a patient with ACH and highlights difficulties of primary total hip arthroplasty (THA) as a treatment option. Intraoperative radiographic imaging is advised to ensure proper prosthesis placement. Femoral osteotomy may aid visualization, reduction, and avoidance of soft tissue injury. Concomitant ACH and DDH is a challenging problem that can be successfully treated with modified THA.

FGFR3/fibroblast growth factor receptor 3 inhibits autophagy through decreasing the ATG12-ATG5 conjugate, leading to the delay of cartilage development in achondroplasia

FGFR3 (fibroblast growth factor receptor 3) is a negative regulator of endochondral ossification. Gain-of-function mutations in FGFR3 are responsible for achondroplasia, the most common genetic form of dwarfism in humans. Autophagy, an evolutionarily conserved catabolic process, maintains chondrocyte viability in the growth plate under stress conditions, such as hypoxia and nutritional deficiencies. However, the role of autophagy and its underlying molecular mechanisms in achondroplasia remain elusive. In this study, we found activated FGFR3 signaling inhibited autophagic activity in chondrocytes, both in vivo and in vitro. By employing an embryonic bone culture system, we demonstrated that treatment with autophagy inhibitor 3-MA or chloroquine led to cartilage growth retardation, which mimics the effect of activated-FGFR3 signaling on chondrogenesis. Furthermore, we found that FGFR3 interacted with ATG12-ATG5 conjugate by binding to ATG5. More intriguingly, FGFR3 signaling was found to decrease the protein level of ATG12-ATG5 conjugate. Consistently, using in vitro chondrogenic differentiation assay system, we showed that the ATG12-ATG5 conjugate was essential for the viability and differentiation of chondrocytes. Transient transfection of ATG5 partially rescued FGFR3-mediated inhibition on chondrocyte viability and differentiation. Our findings reveal that FGFR3 inhibits the autophagic activity by decreasing the ATG12-ATG5 conjugate level, which may play an essential role in the pathogenesis of achondroplasia.

FGFR3 biology and skeletal disease

Fibroblast Growth Factor Receptor 3 (FGFR3) is one of four high-affinity receptors for canonical FGF ligands. It acts in many tissues and plays a special role in skeletal development, especially post-embryonic bone growth, where it inhibits chondrocyte proliferation and differentiation. Gain of function mutations cause the most common forms of dwarfism in humans, and they are also detected in cancer. Triggered by ligand binding or in some cases mutation, FGFR3 activation involves dimerization of receptor monomers, phosphorylation of specific tyrosine residues in the receptor's kinase domain and in the tightly linked scaffold protein Fibroblast Receptor Factor Substrate 2 (FRS2). Signaling molecules recruited to these phosphorylation sites propagate signals through cascades that are subject to modulation. Signal output is also regulated by the fate of the receptor and the interval between its activation and degradation. Trafficking pathways have been identified for both lysosomal and proteasomal degradation, as well as, an alternative fate that involves intramembrane cleavage that produces an intracellular domain fragment capable of nuclear transport and potential function.

Bilateral humeral lengthening in achondroplasia with unilateral external fixators

A retrospective study was performed in 18 patients with achondroplasia, who underwent bilateral humeral lengthening between 2001 and 2013, using monorail external fixators. The mean age was ten years (six to 15) and the mean follow-up was 40 months (12 to 104).

The mean disabilities of the arm, shoulder and hand (DASH) score fell from 32.3 (20 to 40) pre-operatively to 9.4 (6 to 14) post-operatively (p = 0.037). A mean lengthening of 60% (40% to 95%) was required to reach the goal of independent perineal hygiene. One patient developed early consolidation, and fractures occurred in the regenerate bone of four humeri in three patients. There were three transient radial nerve palsies.

Humeral lengthening increases the independence of people with achondroplasia and is not just a cosmetic procedure.

Cite this article: Bone Joint J 2015;97-B:1577–81.

Sheathless transradial coronary angioplasty in an achondroplasic patient with ST elevation myocardial infarction

We present a case of a 50-year-old man with achondroplasia, who presented with anterior ST segment myocardial infarction (STEMI). He was taken urgently to the catheterisation laboratory. Owing to his short stature, it was not possible to insert a radial artery sheath so he underwent a sheathless primary percutaneous coronary intervention (PCI) through the right radial artery, with no complication. He was shifted to the coronary care unit and had an uneventful hospital course. He was discharged in stable condition and follows up regularly as an outpatient.

Multikinase activity of fibroblast growth factor receptor (FGFR) inhibitors SU5402, PD173074, AZD1480, AZD4547 and BGJ398 compromises the use of small chemicals targeting FGFR catalytic activity for therapy of short-stature syndromes

Activating mutations in the fibroblast growth factor receptor 3 (FGFR3) cause the most common genetic form of human dwarfism, achondroplasia (ACH). Small chemical inhibitors of FGFR tyrosine kinase activity are considered to be viable option for treating ACH, but little experimental evidence supports this claim. We evaluated five FGFR tyrosine kinase inhibitors (TKIs) (SU5402, PD173074, AZD1480, AZD4547 and BGJ398) for their activity against FGFR signaling in chondrocytes. All five TKIs strongly inhibited FGFR activation in cultured chondrocytes and limb rudiment cultures, completely relieving FGFR-mediated inhibition of chondrocyte proliferation and maturation. In contrast, TKI treatment of newborn mice did not improve skeletal growth and had lethal toxic effects on the liver, lungs and kidneys. In cell-free kinase assays as well as in vitro and in vivo cell assays, none of the tested TKIs demonstrated selectivity for FGFR3 over three other FGFR tyrosine kinases. In addition, the TKIs exhibited significant off-target activity when screened against a panel of 14 unrelated tyrosine kinases. This was most extensive in SU5402 and AZD1480, which inhibited DDR2, IGF1R, FLT3, TRKA, FLT4, ABL and JAK3 with efficiencies similar to or greater than those for FGFR. Low target specificity and toxicity of FGFR TKIs thus compromise their use for treatment of ACH. Conceptually, different avenues of therapeutic FGFR3 targeting should be investigated.

Paleopathological Study of Dwarfism-Related Skeletal Dysplasia in a Late Joseon Dynasty (South Korean) Population

Skeletal dysplasias related to genetic etiologies have rarely been reported for past populations. This report presents the skeletal characteristics of an individual with dwarfism-related skeletal dysplasia from South Korea. To assess abnormal deformities, morphological features, metric data, and computed tomography scans are analyzed. Differential diagnoses include achondroplasia or hypochondroplasia, chondrodysplasia, multiple epiphyseal dysplasia, thalassemia-related hemolytic anemia, and lysosomal storage disease. The diffused deformities in the upper-limb bones and several coarsened features of the craniofacial bones indicate the most likely diagnosis to have been a certain type of lysosomal storage disease. The skeletal remains of EP-III-4-No.107 from the Eunpyeong site, although incomplete and fragmented, provide important clues to the paleopathological diagnosis of skeletal dysplasias.

Advances in treatment of achondroplasia and osteoarthritis

Achondroplasia (ACH) is the prototype and most common of the human chondrodysplasias. It results from gain-of-function mutations that exaggerate the signal output of the fibroblast growth factor receptor 3 (FGFR3), a receptor tyrosine kinase that negatively regulates growth plate activity and linear bone growth. Several approaches to reduce FGFR3 signaling by blocking receptor activation or inhibiting downstream signals have been proposed. Five show promise in preclinical mouse studies. Two candidate therapies target the extracellular domain of FGFR3. The first is a decoy receptor that competes for activating ligands. The second is a synthetic blocking peptide that prevents ligands from binding and activating FGFR3. Two established drugs, statins and meclozine, improve growth of ACH mice. The strongest candidate therapy employs an analog of C-type natriuretic peptide (CNP), which antagonizes the mitogen-activated-protein (MAP) kinase pathway downstream of the FGFR3 receptor and may also act independently in the growth plate. Only the CNP analog has reached clinical trials. Preliminary results of Phase 2 studies show a substantial increase in growth rate of ACH children after six months of therapy with no serious adverse effects. A challenge for drug therapy in ACH is targeting agents to the avascular growth plate. The application of gene therapy in osteoarthritis offers insights because it faces similar technical obstacles. Major advances in gene therapy include the emergence of recombinant adeno-associated virus as the vector of choice, capsid engineering to target vectors to specific tissues, and development of methods to direct vectors to articular chondrocytes.

Best practices in the evaluation and treatment of foramen magnum stenosis in achondroplasia during infancy

Achondroplasia is the most common inherited disorder of bone growth (skeletal dysplasia). Despite this fact, consistent and evidence-based management approaches to recognized, life-threatening complications, such as foramen magnum stenosis, are lacking. This study aims to outline best practice, based on evidence and expert consensus, regarding the diagnosis, assessment, and management of foramen magnum stenosis in achondroplasia during infancy. A panel of 11 multidisciplinary international experts on skeletal dysplasia was invited to participate in a Delphi process. They were: 1) presented with a list of 26 indications and a thorough literature review, 2) given the opportunity to anonymously rate the indications and discuss in face to face discussion; 3) edit the list and rate it in a second round. Those indications with more than 80% agreement were considered as consensual. After two rounds of rating and a face-to-face meeting, consensus was reached to support 22 recommendations for the evaluation and treatment of foramen magnum stenosis in infants with achondroplasia. These recommendations include indications for surgical decompression, ventriculomegaly, and hydrocephalus, sleep-disordered breathing, physical exams and the use of polysomnography and imaging in this condition. We present a consensus-based best practice guidelines consisting of 22 recommendations. It is hoped that these guidelines will lead to more uniform and structured evaluation, standardizing care pathways, and improving mortality and morbidity outcomes for this cohort.

Characterization of membrane protein interactions in plasma membrane derived vesicles with quantitative imaging Förster resonance energy transfer

Here we describe an experimental tool, termed quantitative imaging Förster resonance energy transfer (QI-FRET), that enables the quantitative characterization of membrane protein interactions. The QI-FRET methodology allows us to acquire binding curves and calculate association constants for complex membrane proteins in the native plasma membrane environment. The method utilizes FRET detection, and thus requires that the proteins of interest are labeled with florescent proteins, either FRET donors or FRET acceptors. Since plasma membranes of cells have complex topologies precluding the acquisition of two-dimensional binding curves, the FRET measurements are performed in plasma membrane derived vesicles that bud off cells as a result of chemical or osmotic stress. The results overviewed here are acquired in vesicles produced with an osmotic vesiculation buffer developed in our laboratory, which does not utilize harsh chemicals. The concentrations of the donor-labeled and the acceptor-labeled proteins are determined, along with the FRET efficiencies, in each vesicle. The experiments utilize transient transfection, such that a wide variety of concentrations is sampled. Then, data from hundreds of vesicles are combined to yield dimerization curves. Here we discuss recent findings about the dimerization of receptor tyrosine kinases (RTKs), membrane proteins that control cell growth and differentiation via lateral dimerization in the plasma membrane. We focus on the dimerization of fibroblast growth factor receptor 3 (FGFR3), a RTK that plays a critically important role in skeletal development. We study the role of different FGFR3 domains in FGFR3 dimerization in the absence of ligand, and we show that FGFR3 extracellular domains inhibit unliganded dimerization, while contacts between the juxtamembrane domains, which connect the transmembrane domains to the kinase domains, stabilize the unliganded FGFR3 dimers. Since FGFR3 has been documented to harbor many pathogenic single amino acid mutations that cause skeletal and cranial dysplasias, as well as cancer, we also study the effects of these mutations on dimerization. First, we show that the A391E mutation, linked to Crouzon syndrome with acanthosis nigricans and to bladder cancer, significantly enhances FGFR3 dimerization in the absence of ligand and thus induces aberrant receptor interactions. Second, we present results about the effect of three cysteine mutations that cause thanatophoric dysplasia, a lethal phenotype. Such cysteine mutations have been hypothesized previously to cause constitutive dimerization, but we find instead that they have a surprisingly modest effect on dimerization. Most of the studied pathogenic mutations also altered FGFR3 dimer structure, suggesting that both increases in dimerization propensities and changes in dimer structure contribute to the pathological phenotypes. The results acquired with the QI-FRET method further our understanding of the interactions between FGFR3 molecules and RTK molecules in general. Since RTK dimerization regulates RTK signaling, our findings advance our knowledge of RTK activity in health and disease. The utility of the QI-FRET method is not restricted to RTKs, and we thus hope that in the future the QI-FRET method will be applied to other classes of membrane proteins, such as channels and G protein-coupled receptors.

Fibroblast growth factor signaling in skeletal development and disease

Fibroblast growth factor (FGF) signaling pathways are essential regulators of vertebrate skeletal development. FGF signaling regulates development of the limb bud and formation of the mesenchymal condensation and has key roles in regulating chondrogenesis, osteogenesis, and bone and mineral homeostasis. This review updates our review on FGFs in skeletal development published in Genes & Development in 2002, examines progress made on understanding the functions of the FGF signaling pathway during critical stages of skeletogenesis, and explores the mechanisms by which mutations in FGF signaling molecules cause skeletal malformations in humans. Links between FGF signaling pathways and other interacting pathways that are critical for skeletal development and could be exploited to treat genetic diseases and repair bone are also explored.

Role of the natriuretic peptide system in normal growth and growth disorders

The C-type natriuretic peptide (CNP) and its receptor (NPR-B) are recognized as important regulators of longitudinal growth. Animal models involving CNP or NPR-B genes (Nppc or Npr2) support the fundamental role of CNP/NPR-B for endochondral ossification. Studies with these animals allow the development of potential drug therapies for dwarfism. Polymorphisms in two genes related to the CNP pathway have been implicated in height variability in healthy individuals. Biallelic loss-of-function mutations in NPR-B gene (NPR2) cause acromesomelic dysplasia type Maroteux, a skeletal dysplasia with extremely short stature. Heterozygous mutations in NPR2 are responsible for nonsyndromic familial short stature. Conversely, heterozygous gain-of-function mutations in NPR2 cause tall stature, with a variable phenotype. A phase 2 multicenter and multinational trial is being developed to evaluate a CNP analog treatment for achondroplasia. Pediatricians and endocrinologists must be aware of growth disorders related to natriuretic peptides, although there is still much to be learned about its diagnostic and therapeutic use.

Magnetic resonance evaluation of the knee in children and adolescents with achondroplasia

BACKGROUND

Achondroplasia is the most common form of skeletal dysplasia. Although the radiographic features are well described, MRI features of the knee in achondroplasia have not been reported.

OBJECTIVE

To describe common MRI characteristics of the knee joint in symptomatic children and adolescents with achondroplasia.

MATERIALS AND METHODS

We retrospectively evaluated 10 knee MRI examinations in 8 children and young adults (age range 11-20 years, mean 16.3 years) with achondroplasia. We measured modified Insall-Salvati index, knee flexion angle, anterior cruciate ligament (ACL)-Blumensaat line angle, ACL-tibial angle, posterior cruciate ligament (PCL) angle, intercondylar notch width index, and intercondylar notch depth index. We compared our findings with an age- and gender-matched control group of 20 children (age range 15-18 years; mean 16 years) with normal knee MRIs.

RESULTS

All 10 knees in the achondroplasia group had discoid lateral meniscus; 8 meniscal tears were identified. Patella baja was present in half of the study cases. Greater knee flexion and increased ACL-Blumensaat line and PCL angles were seen in all achondroplasia knees. ACL-tibial angle was similar in the study and in the control group. Children with achondroplasia had deeper A-shape femoral notches that extended more anteriorly than those seen in the control group. MRI findings were confirmed in all seven knees with arthroscopic correlation.

CONCLUSION

Discoid lateral meniscus, often with tear, is a consistent feature in knee MRIs of symptomatic children and adolescents with achondroplasia. Other findings include patella baja, knee flexion, deep A-shape intercondylar notch, increased ACL-Blumensaat line angle and taut PCL.

Occipital foramina development involves localised regulation of mesenchyme proliferation and is independent of apoptosis

Cranial foramina are holes within the skull, formed during development, allowing entry and exit of blood vessels and nerves. Once formed they must remain open, due to the vital structures they contain, i.e. optic nerves, jugular vein, carotid artery, and other cranial nerves and blood vessels. Understanding cranial foramina development is essential as cranial malformations lead to the stenosis or complete closure of these structures, resulting in blindness, deafness, facial paralysis, raised intracranial pressure and lethality. Here we focus on describing early events in the formation of the jugular, carotid and hypoglossal cranial foramina that form in the mesoderm-derived, endochondral occipital bones at the base of the embryonic chick skull. Whole-mount skeletal staining of skulls indicates the appearance of these foramina from HH32/D7.5 onwards. Haematoxylin & eosin staining of sections shows that the intimately associated mesenchyme, neighbouring the contents of these cranial foramina, is initially very dense and gradually becomes sparser as development proceeds. Histological examination also revealed that these foramina initially contain relatively large-diameter nerves, which later become refined, and are closely associated with the blood vessel, which they also innervate within the confines of the foramina. Interestingly cranial foramina in the base of the skull contain blood vessels lacking smooth muscle actin, which suggests these blood vessels belong to glomus body structures within the foramina. The blood vessel shape also appears to dictate the overall shape of the resulting foramina. We initially hypothesised that cranial foramina development could involve targeted proliferation and local apoptosis to cause 'mesenchymal clearing' and the creation of cavities in a mechanism similar to joint cavitation. We find that this is not the case, and propose that a mechanism reliant upon local nerve/blood vessel-derived restriction of ossification may contribute to foramina formation during cranial development.

The Fibroblast Growth Factor signaling pathway

The signaling component of the mammalian Fibroblast Growth Factor (FGF) family is comprised of eighteen secreted proteins that interact with four signaling tyrosine kinase FGF receptors (FGFRs). Interaction of FGF ligands with their signaling receptors is regulated by protein or proteoglycan cofactors and by extracellular binding proteins. Activated FGFRs phosphorylate specific tyrosine residues that mediate interaction with cytosolic adaptor proteins and the RAS-MAPK, PI3K-AKT, PLCγ, and STAT intracellular signaling pathways. Four structurally related intracellular non-signaling FGFs interact with and regulate the family of voltage gated sodium channels. Members of the FGF family function in the earliest stages of embryonic development and during organogenesis to maintain progenitor cells and mediate their growth, differentiation, survival, and patterning. FGFs also have roles in adult tissues where they mediate metabolic functions, tissue repair, and regeneration, often by reactivating developmental signaling pathways. Consistent with the presence of FGFs in almost all tissues and organs, aberrant activity of the pathway is associated with developmental defects that disrupt organogenesis, impair the response to injury, and result in metabolic disorders, and cancer. For further resources related to this article, please visit the WIREs website.

Association of achondroplasia with Down syndrome: difficulty in prenatal diagnosis by sonographic and 3-D helical computed tomographic analyses

Achondroplasia and Down syndrome are relatively common conditions individually. But co-occurrence of both conditions in the same patient is rare and there have been no reports of fetal analysis of this condition by prenatal sonographic and three-dimensional (3-D) helical computed tomography (CT). Prenatal sonographic findings seen in persons with Down syndrome, such as a thickened nuchal fold, cardiac defects, and echogenic bowel were not found in the patient. A prenatal 3-D helical CT revealed a large head with frontal bossing, metaphyseal flaring of the long bones, and small iliac wings, which suggested achondroplasia. In a case with combination of achondroplasia and Down syndrome, it may be difficult to diagnose the co-occurrence prenatally without typical markers of Down syndrome.

Surgical treatment for cervicomedullary compression among infants with achondroplasia

PURPOSE

Achondroplasia is the most common form of dwarfism. Respiratory failure is responsible for most deaths among these children and is often related to cervicomedullary compression (CMC). We present our experience with early cervicomedullary decompression in infants with achondroplasia.

METHODS

Data was retrospectively collected for infants with achondroplasia who underwent CMC decompression between 1998 and 2013. Data included presurgical and postsurgical neurological examinations, MRI scans, and sleep study results.

RESULTS

Ten infants were included. Ages at surgery were 4 to 23 months (12.5 ± 6.88 months). All infants displayed neurological findings prior to surgery, although often subtle. All infants underwent a foramen magnum opening with a wide C1 laminectomy. Following surgery, seven patients (70 %) demonstrated improved neurological status, and one displayed neurological deterioration. Seven patients demonstrated improved sleep quality 1 year after surgery. These patients had a good or improved neurological status following surgery. Preoperative radiological findings included abnormal hyperintense T2 changes in all children (improved following surgery in six children), brainstem distortion in four children (improved in all), and diminished cerebrospinal fluid (CSF) spaces at the level of the foramen magnum in eight children (improved in seven). One child with extensive preoperative T2 changes accompanied by neurological and respiratory decline, deteriorated following surgery, and remains chronically ventilated.

CONCLUSIONS

Infants with achondroplasia are prone to neurological and respiratory symptoms. We believe that early diagnosis and early surgery for decompression of the foramen magnum and C1 lamina can alleviate respiratory symptoms, improve neurological status, and perhaps prevent sudden infant death in this population.

FGFR3 unliganded dimer stabilization by the juxtamembrane domain

Receptor tyrosine kinases (RTKs) conduct biochemical signals upon dimerization in the membrane plane. While RTKs are generally known to be activated in response to ligand binding, many of these receptors are capable of forming unliganded dimers that are likely important intermediates in the signaling process. All 58 RTKs consist of an extracellular (EC) domain, a transmembrane (TM) domain, and an intracellular domain that includes a juxtamembrane (JM) sequence and a kinase domain. Here we investigate directly the effect of the JM domain on unliganded dimer stability of FGFR3, a receptor that is critically important for skeletal development. The data suggest that FGFR3 unliganded dimers are stabilized by receptor-receptor contacts that involve the JM domains. The contribution is significant, as it is similar in magnitude to the stabilizing contribution of a pathogenic mutation and the repulsive contribution of the EC domain. Furthermore, we show that the effects of the JM domain and a TM pathogenic mutation on unliganded FGFR3 dimer stability are additive. We observe that the JM-mediated dimer stabilization occurs when the JM domain is linked to FGFR3 TM domain and not simply anchored to the plasma membrane. These results point to a coordinated stabilization of the unliganded dimeric state of FGFR3 by its JM and TM domains via a mechanism that is distinctly different from the case of another well studied receptor, EGFR.

Advances in Skeletal Dysplasia Genetics

Skeletal dysplasias result from disruptions in normal skeletal growth and development and are a major contributor to severe short stature. They occur in approximately 1/5,000 births, and some are lethal. Since the most recent publication of the Nosology and Classification of Genetic Skeletal Disorders, genetic causes of 56 skeletal disorders have been uncovered. This remarkable rate of discovery is largely due to the expanded use of high-throughput genomic technologies. In this review, we discuss these recent discoveries and our understanding of the molecular mechanisms behind these skeletal dysplasia phenotypes. We also cover potential therapies, unusual genetic mechanisms, and novel skeletal syndromes both with and without known genetic causes. The acceleration of skeletal dysplasia genetics is truly spectacular, and these advances hold great promise for diagnostics, risk prediction, and therapeutic design.

Loss of osteoblast Runx3 produces severe congenital osteopenia

Congenital osteopenia is a bone demineralization condition that is associated with elevated fracture risk in human infants. Here we show that Runx3, like Runx2, is expressed in precommitted embryonic osteoblasts and that Runx3-deficient mice develop severe congenital osteopenia. Runx3-deficient osteoblast-specific (Runx3(fl/fl)/Col1α1-cre), but not chondrocyte-specific (Runx3(fl/fl)/Col1α2-cre), mice are osteopenic. This demonstrates that an osteoblastic cell-autonomous function of Runx3 is required for proper osteogenesis. Bone histomorphometry revealed that decreased osteoblast numbers and reduced mineral deposition capacity in Runx3-deficient mice cause this bone formation deficiency. Neonatal bone and cultured primary osteoblast analyses revealed a Runx3-deficiency-associated decrease in the number of active osteoblasts resulting from diminished proliferation and not from enhanced osteoblast apoptosis. These findings are supported by Runx3-null culture transcriptome analyses showing significant decreases in the levels of osteoblastic markers and increases in the levels of Notch signaling components. Thus, while Runx2 is mandatory for the osteoblastic lineage commitment, Runx3 is nonredundantly required for the proliferation of these precommitted cells, to generate adequate numbers of active osteoblasts. Human RUNX3 resides on chromosome 1p36, a region that is associated with osteoporosis. Therefore, RUNX3 might also be involved in human bone mineralization.

Analysis of the clinical and molecular characteristics of a child with achondroplasia: A case report

Achondroplasia (ACH) is a hereditary dwarfism caused by the disturbed proliferation and differentiation of growth plate chondrocytes, followed by impaired endochondral bone growth. ACH is caused by mutations in the gene encoding the transmembrane receptor, fibroblast growth factor receptor 3 (FGFR3). In total, >90% of patients with ACH have a G1138A mutation in the transmembrane domain of the FGFR3 gene. Patients with ACH usually have no growth hormone (GH) deficiency. The current study presents the case of a four-year-old male with clinical manifestations suggestive of ACH, including a large head, prominent forehead, short upper arms and legs, and short hands with fingers assuming a trident position. The patient showed normal responses to GH provocation tests with L-dopa (peak GH concentration, 42.38 ng/ml) and insulin (peak GH concentration, 23.29 ng/ml during hypoglycemia), but a blunted response to a GH provocation test with arginine (peak GH concentration, 7.31 ng/ml). Furthermore, the GH concentration during exercise was low (4.8 ng/ml). Magnetic resonance imaging revealed a decreased pituitary volume. Thyroid function tests and the levels of sex hormones (follicle stimulating hormone, luteinizing hormone, estradiol, prolactin and progesterone), cortisol and adrenocorticotropic hormone were normal. A heterozygous G1138A mutation within the FGFR3 gene was detected, confirming the diagnosis of ACH. Thus, recombinant human GH therapy (0.1 IU/kg/day) was initiated. At the six-month follow-up, the height, arm span-to-height ratio and lower limb length-to-height ratio of the patient had increased, while the head circumference had decreased. The present results corroborate the finding that the G1138A mutation within FGFR3 is the most common ACH-causing mutation in different populations. GH may be beneficial in the treatment of short stature in ACH patients with subnormal GH secretion.

Human monoclonal antibody fragments targeting matrilin-3 in growth plate cartilage

PURPOSE

Many genetic disorders, including chondrodysplasias, and acquired disorders impair growth plate function, resulting in short and sometimes malformed bones. There are multiple endocrine and paracrine factors that promote chondrogenesis at the growth plate, which could potentially be used to treat these disorders. Targeting these growth factors specifically to the growth plate might augment the therapeutic skeletal effect while diminishing undesirable effects on non-target tissues.

METHODS

Using yeast display technology, we selected single-chain variable antibody fragments that bound to human and mouse matrilin-3, an extracellular matrix protein specifically expressed in cartilage tissue. The ability of the selected antibody fragments to bind matrilin-3 and to bind cartilage tissue in vitro and in vivo was assessed by ELISA and immunohistochemistry.

RESULTS

We identified antibody fragments that bound matrilin-3 with high affinity and also bound with high tissue specificity to cartilage homogenates and to cartilage structures in mouse embryo sections. When injected intravenously in mice, the antibody fragments specifically homed to cartilage.

CONCLUSIONS

Yeast display successfully selected antibody fragments that are able to target cartilage tissue in vivo. Coupling these antibodies to chondrogenic endocrine and paracrine signaling molecules has the potential to open up new pharmacological approaches to treat childhood skeletal growth disorders.

Neutral endopeptidase-resistant C-type natriuretic peptide variant represents a new therapeutic approach for treatment of fibroblast growth factor receptor 3-related dwarfism

Achondroplasia (ACH), the most common form of human dwarfism, is caused by an activating autosomal dominant mutation in the fibroblast growth factor receptor-3 gene. Genetic overexpression of C-type natriuretic peptide (CNP), a positive regulator of endochondral bone growth, prevents dwarfism in mouse models of ACH. However, administration of exogenous CNP is compromised by its rapid clearance in vivo through receptor-mediated and proteolytic pathways. Using in vitro approaches, we developed modified variants of human CNP, resistant to proteolytic degradation by neutral endopeptidase, that retain the ability to stimulate signaling downstream of the CNP receptor, natriuretic peptide receptor B. The variants tested in vivo demonstrated significantly longer serum half-lives than native CNP. Subcutaneous administration of one of these CNP variants (BMN 111) resulted in correction of the dwarfism phenotype in a mouse model of ACH and overgrowth of the axial and appendicular skeletons in wild-type mice without observable changes in trabecular and cortical bone architecture. Moreover, significant growth plate widening that translated into accelerated bone growth, at hemodynamically tolerable doses, was observed in juvenile cynomolgus monkeys that had received daily subcutaneous administrations of BMN 111. BMN 111 was well tolerated and represents a promising new approach for treatment of patients with ACH.

Meclozine promotes longitudinal skeletal growth in transgenic mice with achondroplasia carrying a gain-of-function mutation in the FGFR3 gene

Achondroplasia (ACH) is one of the most common skeletal dysplasias causing short stature owing to a gain-of-function mutation in the FGFR3 gene, which encodes the fibroblast growth factor receptor 3. We found that meclozine, an over-the-counter drug for motion sickness, inhibited elevated FGFR3 signaling in chondrocytic cells. To examine the feasibility of meclozine administration in clinical settings, we investigated the effects of meclozine on ACH model mice carrying the heterozygous Fgfr3(ach) transgene. We quantified the effect of meclozine in bone explant cultures employing limb rudiments isolated from developing embryonic tibiae from Fgfr3(ach) mice. We found that meclozine significantly increased the full-length and cartilaginous primordia of embryonic tibiae isolated from Fgfr3(ach) mice. We next analyzed the skeletal phenotypes of growing Fgfr3(ach) mice and wild-type mice with or without meclozine treatment. In Fgfr3(ach) mice, meclozine significantly increased the body length after 2 weeks of administration. At skeletal maturity, the bone lengths including the cranium, radius, ulna, femur, tibia, and vertebrae were significantly longer in meclozine-treated Fgfr3(ach) mice than in untreated Fgfr3(ach) mice. Interestingly, meclozine also increased bone growth in wild-type mice. The plasma concentration of meclozine during treatment was within the range that has been used in clinical settings for motion sickness. Increased longitudinal bone growth in Fgfr3(ach) mice by oral administration of meclozine in a growth period suggests potential clinical feasibility of meclozine for the improvement of short stature in ACH.

A recurrent regulatory change underlying altered expression and Wnt response of the stickleback armor plates gene EDA

Armor plate changes in sticklebacks are a classic example of repeated adaptive evolution. Previous studies identified ectodysplasin (EDA) gene as the major locus controlling recurrent plate loss in freshwater fish, though the causative DNA alterations were not known. Here we show that freshwater EDA alleles have cis-acting regulatory changes that reduce expression in developing plates and spines. An identical T → G base pair change is found in EDA enhancers of divergent low-plated fish. Recreation of the T → G change in a marine enhancer strongly reduces expression in posterior armor plates. Bead implantation and cell culture experiments show that Wnt signaling strongly activates the marine EDA enhancer, and the freshwater T → G change reduces Wnt responsiveness. Thus parallel evolution of low-plated sticklebacks has occurred through a shared DNA regulatory change, which reduces the sensitivity of an EDA enhancer to Wnt signaling, and alters expression in developing armor plates while preserving expression in other tissues.

DOI:http://dx.doi.org/10.7554/eLife.05290.001

Stickleback fish develop bony plates on their surface to protect themselves from predators. The extent and pattern of their bony armor depends on their habitat: marine sticklebacks are typically covered from head to tail with bony plates, but freshwater sticklebacks retain only a few plates on their sides.

One gene that promotes the formation of the bony plates is called ectodysplasin (EDA). This encodes a signaling protein that is important for the development of the skeleton, skin and many other tissues. Variations in the sequence of this gene are shared among different stickleback populations worldwide. However, it has not been clear which genetic changes can explain how lightly armored freshwater sticklebacks could have evolved from their well-armored marine ancestors on several separate occasions.

Here, O'Brown et al. studied EDA in marine and groups of freshwater sticklebacks that have evolved in different locations around the world. The experiments show that the level of expression of EDA in the developing plates and spines is lower in the freshwater fish. O'Brown et al. thought this could be due to genetic changes in regions of EDA that lie outside the region that encodes the protein, so called ‘regulatory elements’.

Indeed, further experiments found that all freshwater fish have a small change in the DNA of a regulatory element that switches on the gene in plate-forming regions of the body. When this change was introduced into marine sticklebacks, the fish had lower levels of gene expression in these plate-forming regions.

These findings demonstrate that lightly armored sticklebacks have evolved multiple times from their well-armored marine ancestors through the same small change in their DNA that alters the expression of the EDA gene. The next challenge will be to understand why this particular small change in DNA appears to be favored over all the other changes that could occur in the regulatory element, and to see if factors that act through this regulatory switch also modify armor structures in natural populations.

DOI:http://dx.doi.org/10.7554/eLife.05290.002

Achondroplasia in children: correlation of ventriculomegaly, size of foramen magnum and jugular foramina, and emissary vein enlargement

PURPOSE

Achondroplasia is a skeletal dysplasia with diminished growth of the skull base secondary to defective enchondral bone formation. This leads to narrowing of the foramen magnum and jugular foramina, which further leads to ventricular dilatation and prominence of the emissary veins. The primary goal of our study was to determine a correlation between the degree of ventricular dilatation, jugular foramina and foramen magnum narrowing, as well as emissary vein enlargement.

METHODS

Conventional T2-weighted MR images were evaluated for surface area of the foramen magnum and jugular foramina, ventricular dilatation, and emissary veins enlargement in 16 achondroplasia patients and 16 age-matched controls. Ratios were calculated for the individual parameters using median values from age-matched control groups to avoid age as a confounder.

RESULTS

Compared to age-matched controls, in children with achondroplasia, the surface area of the foramen magnum (median 0.50 cm(2), range 0.23-1.37 cm(2) vs. 3.14 cm(2), 1.83-6.68 cm(2), p < 0.001) and jugular foramina (median 0.02 cm(2), range 0-0.10 cm(2) vs. 0.21 cm(2), 0.03-0.61 cm(2), p < 0.001) were smaller, whereas ventricular dilatation (0.28, 0.24-0.4 vs. 0.26, 0.21-0.28, p < 0.001) and enlargement of emissary veins (6, 0-11 vs. 0, p < 0.001) were higher. Amongst the patients, Spearman correlation and multiple regression analysis did not reveal correlation for severity between the individual parameters.

CONCLUSIONS

Our study suggests that in children with achondroplasia, (1) the variation in ventricular dilatation may be related to an unquantifiable interdependent relationship of emissary vein enlargement, venous channel narrowing, and foramen magnum compression and (2) stable ventricular size facilitated by interdependent factors likely obviates the need for ventricular shunt placement.

Autologous fat graft as treatment of post short stature surgical correction scars

INTRODUCTION

Surgical limb lengthening is undertaken to correct pathological short stature. Among the possible complications related to this procedure, painful and retractile scars are a cause for both functional and cosmetic concern. Our team has already shown the efficacy of autologous fat grafting in the treatment of scars with varying aetiology, so we decided to apply this technique to scars related to surgical correction of dwarfism. A prospective study was conducted to evaluate the efficacy of autologous fat grafting in the treatment of post-surgical scars in patients with short-limb dwarfism using durometer measurements and a modified patient and observer scar assessment scale (POSAS), to which was added a parameter to evaluate movement impairment.

PATIENTS AND METHODS

Between January 2009 and September 2012, 36 children (28 female and 8 male) who presented retractile and painful post-surgical scars came to our unit and were treated with autologous fat grafting. Preoperative and postoperative mean durometer measurements were analysed using the analysis of variance (ANOVA) test and POSAS parameters were studied using the Wilcoxon rank sum test.

RESULTS

There was a statistically significant reduction in all durometer measurements (p-value <0.05) and in all but one of the POSAS parameters (p-value <0.05) following treatment with autologous fat grafting.

DISCUSSION

Surgical procedures to camouflage scars on lower limbs are not often used as a first approach and non-surgical treatments often lead to unsatisfactory results. In contrast, our autologous fat grafting technique in the treatment of post-surgical scars has been shown to be a valuable option in patients with short-limb dwarfism.

CONCLUSION

There was a reduction of skin hardness and a clinical improvement of all POSAS parameters in all patients treated. Moreover, the newly introduced POSAS parameter appears to be reliable and we recommend that it is included to give a more complete evaluation of patient perception.

Molecular, phenotypic aspects and therapeutic horizons of rare genetic bone disorders

A rare disease afflicts less than 200,000 individuals, according to the National Organization for Rare Diseases (NORD) of the United States. Over 6,000 rare disorders affect approximately 1 in 10 Americans. Rare genetic bone disorders remain the major causes of disability in US patients. These rare bone disorders also represent a therapeutic challenge for clinicians, due to lack of understanding of underlying mechanisms. This systematic review explored current literature on therapeutic directions for the following rare genetic bone disorders: fibrous dysplasia, Gorham-Stout syndrome, fibrodysplasia ossificans progressiva, melorheostosis, multiple hereditary exostosis, osteogenesis imperfecta, craniometaphyseal dysplasia, achondroplasia, and hypophosphatasia. The disease mechanisms of Gorham-Stout disease, melorheostosis, and multiple hereditary exostosis are not fully elucidated. Inhibitors of the ACVR1/ALK2 pathway may serve as possible therapeutic intervention for FOP. The use of bisphosphonates and IL-6 inhibitors has been explored to be useful in the treatment of fibrous dysplasia, but more research is warranted. Cell therapy, bisphosphonate polytherapy, and human growth hormone may avert the pathology in osteogenesis imperfecta, but further studies are needed. There are still no current effective treatments for these bone disorders; however, significant promising advances in therapeutic modalities were developed that will limit patient suffering and treat their skeletal disabilities.

Sleep and sleep disorders in rare hereditary diseases: a reminder for the pediatrician, pediatric and adult neurologist, general practitioner, and sleep specialist

Although sleep abnormalities in general and sleep-related breathing disorders (SBD) in particular are quite common in healthy children; their presence is notably under-recognized. Impaired sleep is a frequent problem in subjects with inborn errors of metabolism as well as in a variety of genetic disorders; however, they are commonly either missed or underestimated. Moreover, the complex clinical presentation and the frequently life-threatening symptoms are so overwhelming that sleep and its quality may be easily dismissed. Even centers, which specialize in rare genetic-metabolic disorders, are expected to see only few patients with a particular syndrome, a fact that significantly contributes to the under-diagnosis and treatment of impaired sleep in this particular population. Many of those patients suffer from reduced life quality associated with a variable degree of cognitive impairment, which may be worsened by poor sleep and abnormal ventilation during sleep, abnormalities which can be alleviated by proper treatment. Even when such problems are detected, there is a paucity of publications on sleep and breathing characteristics of such patients that the treating physician can refer to. In the present paper, we provide an overview of sleep and breathing characteristics in a number of rare genetic–metabolic disorders with the hope that it will serve as a reminder for the medical professional to look for possible impaired sleep and SBD in their patients and when present to apply the appropriate evaluation and treatment options.

Cellular and molecular bases of skeletal regeneration: what can we learn from genetic mouse models?

Although bone repairs through a very efficient regenerative process in 90% of the patients, many factors can cause delayed or impaired healing. To date, there are no reliable biological parameters to predict or diagnose bone repair defects. Orthopedic surgeons mostly base their diagnoses on radiographic analyses. With the recent progress in our understanding of the bone repair process, new methods may be envisioned. Animal models have allowed us to define the key steps of bone regeneration and the biological and mechanical factors that may influence bone healing in positive or negative ways. Most importantly, small animal models such as mice have provided powerful tools to apprehend the genetic bases of normal and impaired bone healing. The current review presents a state of the art of the genetically modified mouse models that have advanced our understanding of the cellular and molecular components of bone regeneration and repair. The review illustrates the use of these models to define the role of inflammation, skeletal cell lineages, signaling pathways, the extracellular matrix, osteoclasts and angiogenesis. These genetic mouse models promise to change the field of orthopedic surgery to help establish genetic predispositions for delayed repair, develop models of non-union that mimic the human conditions and elaborate new therapeutic approaches to enhance bone regeneration.