Humeroradial synostosis (HRS) is a rare congenital limb malformation, characterised by fusion of the humeral and radial bones, leading to functional disability of the elbow joint. HRS may be reported in familial or sporadic cases and observed either isolated or as part of a syndromic condition. According to an extensive review of the literature, a dozen known conditions may comprise an HRS. The present review aims to propose an updated classification based on molecular pathways (chondrogenesis and osteogenesis; limb development and patterning; genome regulation), combined with a concise overview of the conditions associated with HRS. This knowledge could guide molecular analyses, patient management and genetic counselling. As some cases remain unexplained, further genetic and epidemiological studies are required to evaluate the contribution of genetic and environmental factors in HRS physiopathology.

Clubfoot, medically termed congenital talipes equinovarus (CTEV), is a prevalent musculoskeletal birth defect, affecting approximately 0.3% of all live births. This serious congenital anomaly results from structural abnormalities in the foot and lower leg, leading to abnormal positioning of the ankle and foot joints. This review provides a comprehensive overview of the causative factors associated with CTEV and evaluates current therapeutic approaches. Although variations in genes encoding contractile proteins of skeletal myofibers have been proposed as contributors to the etiology of CTEV, no definitive candidate genes have been conclusively linked to increased risk. However, genes such as TBX4, PITX1, and members of the HOXA, HOXC, and HOXD clusters, as well as NAT2, have been implicated in the condition's development, playing critical roles in limb development, muscle formation, and tissue differentiation. Also, Axin1 plays a key role in joint formation and skeletal development by inhibiting β-catenin-BMP signaling. It could significantly serve as a therapeutic target for fibular hemimelia and multiple synostoses syndrome. The exact mechanisms and the extent of their physical and genetic interactions remain subjects of ongoing research. Understanding the genetic determinants and cellular pathways involved in CTEV is crucial for unravelling the pathophysiology of this complex deformity.

Humans and other jawed vertebrates rely heavily on their craniofacial skeleton for eating, breathing, and communicating. As such, it is vital that the elements of the craniofacial skeleton develop properly during embryogenesis to ensure a high quality of life and evolutionary fitness. Indeed, craniofacial abnormalities, including cleft palate and craniosynostosis, represent some of the most common congenital abnormalities in newborns. Like many other organ systems, the development of the craniofacial skeleton is complex, relying on specification and migration of the neural crest, patterning of the pharyngeal arches, and morphogenesis of each skeletal element into its final form. These processes must be carefully coordinated and integrated. One way this is achieved is through the spatial and temporal deployment of cell signaling pathways. Recent studies conducted using the zebrafish model underscore the importance of the Transforming Growth Factor Beta (TGF-β) and Bone Morphogenetic Protein (BMP) pathways in craniofacial development. Although both pathways contain similar components, each pathway results in unique outcomes on a cellular level. In this review, we will cover studies conducted using zebrafish that show the necessity of these pathways in each stage of craniofacial development, starting with the induction of the neural crest, and ending with the morphogenesis of craniofacial elements. We will also cover human skeletal and craniofacial diseases and malformations caused by mutations in the components of these pathways (e.g., cleft palate, craniosynostosis, etc.) and the potential utility of zebrafish in studying the etiology of these diseases. We will also briefly cover the utility of the zebrafish model in joint development and biology and discuss the role of TGF-β/BMP signaling in these processes and the diseases that result from aberrancies in these pathways, including osteoarthritis and multiple synostoses syndrome. Overall, this review will demonstrate the critical roles of TGF-β/BMP signaling in craniofacial development and show the utility of the zebrafish model in development and disease.

This study aimed to identify the molecular defects and clinical manifestations in a Chinese family with brachydactyly (BD) type A1 (BDA1) and multiple-synostoses syndrome 2 (SYNS2). A Chinese family with BDA1 and SYNS2 was enrolled in this study. Whole-exome sequencing was used to analyze the gene variants in the proband. The sequences of the candidate pathogenic variant in GDF5 was validated via Sanger sequencing. I-TASSER and PyMOL were used to analyze the functional domains of the corresponding mutant proteins. The family was found to have an autosomal-dominantly inherited combination of BDA1 and SYNS2 caused by the S475N variant in the GDF5 gene. The variant was located within the functional region, and the mutated residue was found to be highly conserved among species. Via bioinformatic analyses, we predicted this variant to be deleterious, which perturb the protein function. The substitution of the negatively charged amino acid S475 with the neutral N475 was predicted to disrupt the formation of salt bridges with Y487 and impair the structure, stability, and function of the protein, consequently, the abnormalities in cartilage and bone development ensue. A single genetic variant (S475N) which disrupt the formation of salt bridges with Y487, in the interface of the antagonist- and receptor-binding sites of GDF5 concurrently causes two pathological mechanisms. This is the first report of this variant, identified in a Chinese family with BDA1 and SYNS2.