BBS9 gene in nonsyndromic craniosynostosis: Role of the primary cilium in the aberrant ossification of the suture osteogenic niche

Identification of bone metabolism disorders in patients with Alström and Bardet-Biedl syndromes based on markers of bone turnover and mandibular atrophy

Objectives

Causative variants in genes responsible for Alström syndrome (ALMS) and Bardet-Biedl syndrome (BBS) cause damage to primary cilia associated with correct functioning of cell signaling pathways in many tissues. Despite differences in genetic background, both syndromes affect multiple organs and numerous clinical manifestations are common including obesity, retinal degeneration, insulin resistance, type 2 diabetes and many others. The aim of the study was to evaluate bone metabolism abnormalities and their relation to metabolic disorders based on bone turnover markers and presence of mandibular atrophy in patients with ALMS and BBS syndromes.

Material and methods

In 18 patients (11 with ALMS and 7 with BBS aged 5–29) and in 42 age-matched (p < 0.05) healthy subjects, the following markers of bone turnover were assessed: serum osteocalcin (OC), osteoprotegerin (OPG), s-RANKL and urinary deoxypyridinoline - DPD. In addition, a severity of alveolar atrophy using dental panoramic radiograms was evaluated.

Results

Lower serum OC (p = 0.0004) and urinary DPD levels (p = 0.0056) were observed in the study group compared to controls. In ALMS and BBS patients, serum OC and urinary DPD values negatively correlated with the HOMA-IR index, while a positive correlation between the OC and 25-OHD levels and a negative correlation between s-RANKL and fasting glucose concentrations were found. A significant difference in the incidence of low-grade mandibular atrophy between patients with ALMS and BBS and controls (p < 0.0001) was observed.

Conclusions

The identification of bone metabolism disorders in patients with ALMS and BBS syndromes indicates the necessity to provide them with appropriate diagnosis and treatment of these abnormalities.

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Bone metabolism disorders in Alstrom and Bardet-Biedl syndromes

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Markers of bone turnover in Alstrom and Bardet-Biedl syndromes

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Mandibular atrophy in Alstrom and Bardet-Biedl syndromes

Meier-Gorlin Syndrome: Clinical Misdiagnosis, Genetic Testing and Functional Analysis of ORC6 Mutations and the Development of a Prenatal Test

Meier−Gorlin syndrome (MGS) is a rare genetic developmental disorder that causes primordial proportional dwarfism, microtia, the absence of or hypoplastic patellae and other skeletal anomalies. Skeletal symptoms overlapping with other syndromes make MGS difficult to diagnose clinically. We describe a 3-year-old boy with short stature, recurrent respiratory infections, short-rib dysplasia, tower head and facial dysmorphisms who was admitted to the Tomsk Genetic Clinic to verify a clinical diagnosis of Jeune syndrome. Clinical exome sequencing revealed two variants (compound heterozygosity) in the ORC6 gene: c.2T>C(p.Met1Thr) and c.449+5G>A. In silico analysis showed the pathogenicity of these two mutations and predicted a decrease in donor splicing site strength for c.449+5G>A. An in vitro minigene assay indicated that variant c.449+5G>A causes complete skipping of exon 4 in the ORC6 gene. The parents requested urgent prenatal testing for MGS for the next pregnancy, but it ended in a miscarriage. Our results may help prevent MGS misdiagnosis in the future. We also performed in silico and functional analyses of ORC6 mutations and developed a restriction fragment length polymorphism and haplotype-based short-tandem-repeat assay for prenatal genetic testing for MGS. These findings should elucidate MGS etiology and improve the quality of genetic counselling for affected families.

MTHSA-DHEI: multitasking harmony search algorithm for detecting high-order SNP epistatic interactions

Genome-wide association studies have succeeded in identifying genetic variants associated with complex diseases, but the findings have not been well interpreted biologically. Although it is widely accepted that epistatic interactions of high-order single nucleotide polymorphisms (SNPs) [(1) Single nucleotide polymorphisms (SNP) are mainly deoxyribonucleic acid (DNA) sequence polymorphisms caused by variants at a single nucleotide at the genome level. They are the most common type of heritable variation in humans.] are important causes of complex diseases, the combinatorial explosion of millions of SNPs and multiple tests impose a large computational burden. Moreover, it is extremely challenging to correctly distinguish high-order SNP epistatic interactions from other high-order SNP combinations due to small sample sizes. In this study, a multitasking harmony search algorithm (MTHSA-DHEI) is proposed for detecting high-order epistatic interactions [(2) In classical genetics, if genes X1 and X2 are mutated and each mutation by itself produces a unique disease status (phenotype) but the mutations together cause the same disease status as the gene X1 mutation, gene X1 is epistatic and gene X2 is hypostatic, and gene X1 has an epistatic effect (main effect) on disease status. In this work, a high-order epistatic interaction occurs when two or more SNP loci have a joint influence on disease status.], with the goal of simultaneously detecting multiple types of high-order (k1-order, k2-order, …, kn-order) SNP epistatic interactions. Unified coding is adopted for multiple tasks, and four complementary association evaluation functions are employed to improve the capability of discriminating the high-order SNP epistatic interactions. We compare the proposed MTHSA-DHEI method with four excellent methods for detecting high-order SNP interactions for 8 high-orderepistatic interaction models with no marginal effect (EINMEs) and 12 epistatic interaction models with marginal effects (EIMEs) (*) and implement the MTHSA-DHEI algorithm with a real dataset: age-related macular degeneration (AMD). The experimental results indicate that MTHSA-DHEI has power and an F1-score exceeding 90% for all EIMEs and five EINMEs and reduces the computational time by more than 90%. It can efficiently perform multiple high-order detection tasks for high-order epistatic interactions and improve the discrimination ability for diverse epistasis models.

Primary cilia and PTH1R interplay in the regulation of osteogenic actions

Primary cilia are subcellular structures specialized in sensing different stimuli in a diversity of cell types. In bone, the primary cilium is involved in mechanical sensing and transduction of signals that regulate the behavior of mesenchymal osteoprogenitors, osteoblasts and osteocytes. To perform its functions, the primary cilium modulates a plethora of molecules including those stimulated by the parathyroid hormone (PTH) receptor type I (PTH1R), a master regulator of osteogenesis. Binding of the agonists PTH or PTH-related protein (PTHrP) to the PTH1R or direct agonist-independent stimulation of the receptor activate PTH1R signaling pathways. In turn, activation of PTH1R leads to regulation of bone formation and remodeling. Herein, we describe the structure, function and molecular partners of primary cilia in the context of bone, playing special attention to those signaling pathways that are mediated directly or indirectly by PTH1R in association with primary cilia during the process of osteogenesis.

Shaping modern human skull through epigenetic, transcriptional and post-transcriptional regulation of the RUNX2 master bone gene

RUNX2 encodes the master bone transcription factor driving skeletal development in vertebrates, and playing a specific role in craniofacial and skull morphogenesis. The anatomically modern human (AMH) features sequence changes in the RUNX2 locus compared with archaic hominins' species. We aimed to understand how these changes may have contributed to human skull globularization occurred in recent evolution. We compared in silico AMH and archaic hominins' genomes, and used mesenchymal stromal cells isolated from skull sutures of craniosynostosis patients for in vitro functional assays. We detected 459 and 470 nucleotide changes in noncoding regions of the AMH RUNX2 locus, compared with the Neandertal and Denisovan genomes, respectively. Three nucleotide changes in the proximal promoter were predicted to alter the binding of the zinc finger protein Znf263 and long-distance interactions with other cis-regulatory regions. By surface plasmon resonance, we selected nucleotide substitutions in the 3'UTRs able to affect miRNA binding affinity. Specifically, miR-3150a-3p and miR-6785-5p expression inversely correlated with RUNX2 expression during in vitro osteogenic differentiation. The expression of two long non-coding RNAs, AL096865.1 and RUNX2-AS1, within the same locus, was modulated during in vitro osteogenic differentiation and correlated with the expression of specific RUNX2 isoforms. Our data suggest that RUNX2 may have undergone adaptive phenotypic evolution caused by epigenetic and post-transcriptional regulatory mechanisms, which may explain the delayed suture fusion leading to the present-day globular skull shape.

Ciliary Signalling and Mechanotransduction in the Pathophysiology of Craniosynostosis

Craniosynostosis (CS) is the second most prevalent inborn craniofacial malformation; it results from the premature fusion of cranial sutures and leads to dimorphisms of variable severity. CS is clinically heterogeneous, as it can be either a sporadic isolated defect, more frequently, or part of a syndromic phenotype with mendelian inheritance. The genetic basis of CS is also extremely heterogeneous, with nearly a hundred genes associated so far, mostly mutated in syndromic forms. Several genes can be categorised within partially overlapping pathways, including those causing defects of the primary cilium. The primary cilium is a cellular antenna serving as a signalling hub implicated in mechanotransduction, housing key molecular signals expressed on the ciliary membrane and in the cilioplasm. This mechanical property mediated by the primary cilium may also represent a cue to understand the pathophysiology of non-syndromic CS. In this review, we aimed to highlight the implication of the primary cilium components and active signalling in CS pathophysiology, dissecting their biological functions in craniofacial development and in suture biomechanics. Through an in-depth revision of the literature and computational annotation of disease-associated genes we categorised 18 ciliary genes involved in CS aetiology. Interestingly, a prevalent implication of midline sutures is observed in CS ciliopathies, possibly explained by the specific neural crest origin of the frontal bone.

Gain-of-function variants and overexpression of RUNX2 in patients with nonsyndromic midline craniosynostosis

Craniosynostosis (CS), the premature fusion of one or more cranial sutures, is a relatively common congenital anomaly, occurring in 3-5 per 10,000 live births. Nonsyndromic CS (NCS) accounts for up to 80% of all CS cases, yet the genetic factors contributing to the disorder remain largely unknown. The RUNX2 gene, encoding a transcription factor critical for bone and skull development, is a well known CS candidate gene, as copy number variations of this gene locus have been found in patients with syndromic craniosynostosis. In the present study, we aimed to characterize RUNX2 to better understand its role in the genetic etiology and in the molecular mechanisms underlying midline suture ossification in NCS. We report four nonsynonymous variants, one intronic variant and one 18 bp in-frame deletion in RUNX2 not found in our study control population. Significant difference in allele frequency (AF) for the deletion variant RUNX2 p.Ala84-Ala89del (ClinVar 257,095; dbSNP rs11498192) was observed in our sagittal NCS cohort when compared to the general population (P = 1.28 × 10^-6), suggesting a possible role in the etiology of NCS. Dual-luciferase assays showed that three of four tested RUNX2 variants conferred a gain-of-function effect on RUNX2, further suggesting their putative pathogenicity in the tested NCS cases. Downregulation of RUNX2 expression was observed in prematurely ossified midline sutures. Metopic sites showed significant downregulation of promoter 1-specific isoforms compared to sagittal sites. Suture-derived mesenchymal stromal cells showed an increased expression of RUNX2 over matched unfused suture derived cells. This demonstrates that RUNX2, and particularly the distal promoter 1-isoform group, are overexpressed in the osteogenic precursors within the pathological suture sites.

GLI1 and AXIN2 Are Distinctive Markers of Human Calvarial Mesenchymal Stromal Cells in Nonsyndromic Craniosynostosis

All skeletal bones house osteogenic stem cell niches, in which mesenchymal stromal cells (MSC) provide progenitors for tissue growth and regeneration. They have been widely studied in long bones formed through endochondral ossification. Limited information is available on the composition of the osteogenic niche in flat bones (i.e., skull vault bones) that develop through direct membranous ossification. Craniosynostosis (CS) is a congenital craniofacial defect due to the excessive and premature ossification of skull vault sutures. This study aimed at analysing the expression of GLI1, AXIN2 and THY1 in the context of the human skull vault, using nonsyndromic forms of CS (NCS) as a model to test their functional implication in the aberrant osteogenic process. The expression of selected markers was studied in NCS patients' calvarial bone specimens, to assess the in vivo location of cells, and in MSC isolated thereof. The marker expression profile was analysed during in vitro osteogenic differentiation to validate the functional implication. Our results show that GLI1 and AXIN2 are expressed in periosteal and endosteal locations within the osteogenic niche of human calvarial bones. Their expression is higher in MSC isolated from calvarial bones than in those isolated from long bones and tends to decrease upon osteogenic commitment and differentiation. In particular, AXIN2 expression was lower in cells isolated from prematurely fused sutures than in those derived from patent sutures of NCS patients. This suggests that AXIN2 could reasonably represent a marker for the stem cell population that undergoes depletion during the premature ossification process occurring in CS.

Graphene Oxide Nano-Concentrators Selectively Modulate RNA Trapping According to Metal Cations in Solution

With recent advances in nanotechnology, graphene nanomaterials are being translated to applications in the fields of biosensing, medicine, and diagnostics, with unprecedented power. Graphene is a carbon allotrope derived from graphite exfoliation made of an extremely thin honeycomb of sp2 hybridized carbons. In comparison with the bulk materials, graphene and its water-soluble derivative graphene oxide have a smaller size suitable for diagnostic platform miniaturization as well as high surface area and consequently loading of a large number of biological probes. In this work, we propose a nanotechnological method for concentrating total RNA solution and/or enriching small RNA molecules. To this aim, we exploited the unique trapping effects of GO nanoflakes in the presence of divalent cations (i.e., calcium and magnesium) that make it flocculate and precipitate, forming complex meshes that are positively charged. Here, we demonstrated that GO traps can concentrate nucleic acids in the presence of divalent cations and that small RNAs can be selectively released from GO-magnesium traps. GO nano-concentrators will allow better analytical performance with samples available in small amounts and will increase the sensitivity of sequencing platforms by short RNA selection.

Tissue-dependent differences in Bardet-Biedl syndrome gene expression

BACKGROUND INFORMATION

Primary cilia are highly conserved multifunctional cell organelles that extend from the cell membrane. A range of genetic disorders, collectively termed ciliopathies, is attributed to primary cilia dysfunction. The archetypical ciliopathy is the Bardet-Biedl syndrome (BBS), patients of which display virtually all symptoms associated with dysfunctional cilia. The primary cilium acts as a sensory organelle transmitting intra- and extracellular signals thereby transducing various signalling pathways facilitated by the BBS proteins. Growing evidence suggests that cilia proteins also have alternative functions in ciliary independent mechanisms, which might be contributing to disease etiology.

RESULTS

In an attempt to gain more insight into possible differences in organ specific roles, we examined whether relative gene expression for individual Bbs genes was constant across different tissues in mouse, in order to distinguish possible differences in organ specific roles. All tested tissues show differentially expressed Bbs transcripts with some tissues showing a more similar stoichiometric composition of transcripts than others do.  However, loss of Bbs6 or Bbs8 affects expression of other Bbs transcripts in a tissue-dependent way.

CONCLUSIONS AND SIGNIFICANCE

Our data support the hypothesis that in some organs, BBS proteins not only function in a complex but might also have alternative functions in a ciliary independent context. This significantly alters our understanding of disease pathogenesis and development of possible treatment strategies.

Imaging in craniosynostosis: when and what?

PURPOSE

Currently, the interest on craniosynostosis in the clinical practice is raised by their increased frequency and their genetic implications other than by the still existing search of less invasive surgical techniques. These reasons, together with the problem of legal issues, make the need of a definite diagnosis for a crucial problem, even in single-suture craniosynostosis (SSC). Although the diagnosis of craniosynostosis is primarily the result of physical examination, craniometrics measuring, and observation of the skull deformity, the radiological assessment currently plays an important role in the confirmation of the diagnosis, the surgical planning, and even the postoperative follow-up. On the other hand, in infants, the use of radiation or the need of sedation/anesthesia raises the problem to reduce them to minimum to preserve such a delicate category of patient from their adverse effects.

METHODS, RESULTS AND CONCLUSIONS

This review aims at summarizing the state of the art of the role of radiology in craniosynostosis, mainly focusing on indications and techniques, to provide an update not only to pediatric neurosurgeons or maxillofacial surgeons but also to all the other specialists involved in their management, like neonatologists, pediatricians, clinical geneticists, and pediatric neurologists.