Dominant negative variants in KIF5B cause osteogenesis imperfecta via down regulation of mTOR signaling.

BACKGROUND: Kinesin motor proteins transport intracellular cargo, including mRNA, proteins, and organelles. Pathogenic variants in kinesin-related genes have been implicated in neurodevelopmental disorders and skeletal dysplasias. We identified de novo, heterozygous variants in KIF5B, encoding a kinesin-1 subunit, in four individuals with osteogenesis imperfecta. The variants cluster within the highly conserved kinesin motor domain and are predicted to interfere with nucleotide binding, although the mechanistic consequences on cell signaling and function are unknown. METHODS: To understand the in vivo genetic mechanism of KIF5B variants, we modeled the p.Thr87Ile variant that was found in two patients in the C. elegans ortholog, unc-116, at the corresponding position (Thr90Ile) by CRISPR/Cas9 editing and performed functional analysis. Next, we studied the cellular and molecular consequences of the recurrent p.Thr87Ile variant by microscopy, RNA and protein analysis in NIH3T3 cells, primary human fibroblasts and bone biopsy. RESULTS: C. elegans heterozygous for the unc-116 Thr90Ile variant displayed abnormal body length and motility phenotypes that were suppressed by additional copies of the wild type allele, consistent with a dominant negative mechanism. Time-lapse imaging of GFP-tagged mitochondria showed defective mitochondria transport in unc-116 Thr90Ile neurons providing strong evidence for disrupted kinesin motor function. Microscopy studies in human cells showed dilated endoplasmic reticulum, multiple intracellular vacuoles, and abnormal distribution of the Golgi complex, supporting an intracellular trafficking defect. RNA sequencing, proteomic analysis, and bone immunohistochemistry demonstrated down regulation of the mTOR signaling pathway that was partially rescued with leucine supplementation in patient cells. CONCLUSION: We report dominant negative variants in the KIF5B kinesin motor domain in individuals with osteogenesis imperfecta. This study expands the spectrum of kinesin-related disorders and identifies dysregulated signaling targets for KIF5B in skeletal development.

Postmortem CT and autopsy findings in an elevator-related death: a case report.

Elevator-related fatalities and injuries are rarely discussed. Falls have been identified as the first cause of mortality in the majority of these accidents. Evidence suggests that many elevator accidents may be attributed to inadequate equipment maintenance or malfunctions of the devices. This study examines a case involving an elevator maintenance worker found within an elevator shaft, using postmortem computed tomography (PMCT) along with a full autopsy. The autopsy revealed that the cause of death was severe polytrauma resulting from dragging, compression, and crushing mechanisms, which resulted in a dislocated skull and multiple thoraco-abdominal injuries, including exposed organs and viscera. Detailed examination identified a cranio-encephalic crush, leading to a significant alteration in the physiognomy of the facial structures. Additionally, PMCT revealed complex spinal fractures, such as a Jefferson fracture and a complete Chance fracture at the D6 vertebra, accompanied by spinal deviation proximal to the fracture site. Autopsy findings corroborated these PMCT results. A multidisciplinary approach, including PMCT, is proposed as a strategic method for the comprehensive reconstruction of such accidents, facilitating the collection of extensive data.

Osteogenesis imperfecta: advancements in genetics and treatment.

PURPOSE OF REVIEW: The purpose of this review is to outline the current understanding of the molecular mechanisms and natural history of osteogenesis imperfecta, and to describe the development of new treatments for this disorder. RECENT FINDINGS: The introduction of next-generation sequencing technology has led to better understanding of the genetic cause of osteogenesis imperfecta and enabled cost-effective and timely diagnosis via expanded gene panels and exome or genome sequencing. Clinically, despite genetic heterogeneity, different forms of osteogenesis imperfecta share similar features that include connective tissue and systemic manifestations in addition to bone fragility. Thus, the goals of treatment in osteogenesis imperfecta extend beyond decreasing the risk of fracture, to include the maximization of growth and mobility, and the management of extraskeletal complications. The standard of care in pediatric patients is bisphosphonates therapy. Ongoing preclinical studies in osteogenesis imperfecta mouse models and clinical studies in individuals with osteogenesis imperfecta have been instrumental in the development of new and targeted therapeutic approaches, such as sclerostin inhibition and transforming growth factor-ß inhibition. SUMMARY: Osteogenesis imperfecta is a skeletal dysplasia characterized by bone fragility and extraskeletal manifestations. Better understanding of the mechanisms of osteogenesis imperfecta will enable the development of much needed targeted therapies to improve the outcome in affected individuals.

The IFITM5 mutation in osteogenesis imperfecta type V is associated with an ERK/SOX9-dependent osteoprogenitor differentiation defect.

Osteogenesis imperfecta (OI) type V is the second most common form of OI, distinguished by hyperplastic callus formation and calcification of the interosseous membranes, in addition to the bone fragility. It is caused by a recurrent, dominant pathogenic variant (c.-14C>T) in interferon-induced transmembrane protein 5 (IFITM5). Here, we generated a conditional Rosa26-knockin mouse model to study the mechanistic consequences of the recurrent mutation. Expression of the mutant Ifitm5 in osteo-chondroprogenitor or chondrogenic cells resulted in low bone mass and growth retardation. Mutant limbs showed impaired endochondral ossification, cartilage overgrowth, and abnormal growth plate architecture. The cartilage phenotype correlates with the pathology reported in patients with OI type V. Surprisingly, expression of mutant Ifitm5 in mature osteoblasts caused no obvious skeletal abnormalities. In contrast, earlier expression in osteo-chondroprogenitors was associated with an increase in the skeletal progenitor cell population within the periosteum. Lineage tracing showed that chondrogenic cells expressing the mutant Ifitm5 had decreased differentiation into osteoblastic cells in diaphyseal bone. Moreover, mutant IFITM5 disrupted early skeletal homeostasis in part by activating ERK signaling and downstream SOX9 protein, and inhibition of these pathways partially rescued the phenotype in mutant animals. These data identify the contribution of a signaling defect altering osteo-chondroprogenitor differentiation as a driver in the pathogenesis of OI type V.

Microbiological screening tests for SARS-CoV-2 in the first hour since the hospital admission: A reliable tool for enhancing the safety of pediatric care.

Introduction/purpose: Since a significant proportion of SARS-CoV-2 infections occur within healthcare facilities, a multidisciplinary approach is required for careful and timely assessment of the risk of infection in asymptomatic patients or those whose COVID-19 diagnosis has not yet been made. The aim of this study was to investigate whether an adaptative model based on microbiological testing can represent a valid risk management strategy. Material and methods: We collected data from the risk management unit database of a 1,550-bed tertiary hospital (Fondazione Policlinico Gemelli IRCCS, Rome, Italy) concerning pediatric admissions to the Emergency Department (ED) from 1 March 2020 to 31 December 2021. The study period was subdivided in period A and period B according to the technique used for the microbiological screening, respectively reverse-transcription polymerase chain reaction (RT-PCR) and antigen-detection test. Results: In Period A, 426 children (mean age: 6 years) underwent microbiological screening at the ED. The total number of molecular tests performed was 463. 459/463 tested negative at the molecular test. In Period B, 887 children (mean age: 6 years) underwent microbiological screening in the ED. The total number of molecular tests performed was 1,154. 1,117/1,154 tested negative at the molecular test. Neither in Period A nor in Period B hospital-acquired SARS-CoV-2 infections were reported. Discussion and conclusion: Despite high volumes, no cases of hospital-acquired SARS-CoV-2 infection have been reported. SARS-CoV-2 antigen-based tests can be used as a first-line option as they provide rapid results compared to RT-PCR, reducing the risk of infection in ED waiting rooms.