Dominant mutations in the calcium permeable ion channel TRPV4 (transient receptor potential vanilloid 4) typically result in skeletal dysplasia or peripheral neuromuscular disease. However, the full spectrum of TRPV4-related phenotypes remains incompletely defined. This study systematically reviewed the clinical and genetic features of 10 Chinese patients harboring various TRPV4 variants. In the cohort, six patients were diagnosed with spondylometaphyseal dysplasia Kozlowski type (SMDK) and four patients with metatropic dysplasia (MD). The most common features involved spinal deformity (platyspondyly, kyphosis or scoliosis), and lower-limb malalignments (genu varum, genu valgum, or leg-length discrepancy). Two patients with MD had neurological deficits. The R594H and P799R substitutions were the most recurrent variants in our study. A novel variant (c.1628T>G, p.L543R) in the S2-S3 loop was identified. The study seeks to improve diagnostic precision by combining genetic and radiographic assessment, and highlights the importance of early spinal surveillance and multidisciplinary care to prevent neurological complications underlying TRPV4-mediated disorders.

Skeletal syndromes and dysplasias include more than 150 entities, most often of genetic origin. Some of them cause abnormalities in the cervical spine, with or without instability, distortion or compression of the spinal cord. These abnormalities must be detected and treated if necessary because they can have serious consequences such as quadriplegia. Up to 30% of patients with Down syndrome are affected by occipitocervical or atlantoaxial instability. Dynamic cervical spine radiographs are the most common screening tool. Mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage diseases that result in the accumulation of glycosaminoglycans sometimes responsible for craniocervical instability and cervical spinal canal stenosis. Their monitoring requires an MRI every two years. Neurofibromatosis type 1 and syndromes with connective tissue abnormalities (Marfan syndrome, Loeys-Dietz syndrome, Ehlers-Danlos syndrome) can cause severe and unstable cervical spine deformities that may remain asymptomatic for a long time. Cervical X-rays should therefore be performed if there is the slightest doubt. Some rare chondrodysplasias (punctate chondrodysplasia, Larsen syndrome, Metatropic dysplasia) or segmentation anomalies (Klippel Feil syndrome, Sprengel's disease) have cervical spine abnormalities that should be looked for. In case of progression of a deformity (usually kyphosis) or stenosis of the cervical spine, it is important to consider surgical treatment with correction and stabilization. Sometimes preceded by a period of Halo traction, the instrumentation must have "wide" limits and exceed the anatomical limits of the spinal deformity by at least 2-3 levels to prevent the development of an adjacent deformity. The increasing use of surgical navigation techniques allows for greater corrections and more efficient stabilizations, including severe cervical spinal deformities. Vigilance and the detection of these abnormalities remain the key to early and preventive treatment of the complications of these spinal anomalies on often difficult terrain. LEVEL OF EVIDENCE: >V (expert opinion).

Metatropic dysplasia is an autosomal dominant skeletal disorder characterized by progressive kyphoscoliosis, severe platyspondyly, pronounced metaphyseal enlargement, and shortening of the long bones. This condition is caused by pathogenic variants in the TRPV4 (Transient Receptor Potential Vanilloid 4) gene, which encodes a non-selective calcium channel involved in bone homeostasis. Variants in TRPV4 have been associated with two major disease groups: skeletal dysplasias and neuropathies, with recent findings indicating an overlap in their clinical features. We report three patients with metatropic dysplasia, each presenting a distinct severity profile. All exhibited a bell-shaped thorax, significant platyspondyly, and shortened long bones with broad metaphyses. Notably, patients 1 and 3 had more complex clinical courses, including seizures and global developmental delay. Genetic analysis revealed two different TRPV4 variants: p.Asn796del (patient 1) and p.Pro799Leu (patients 2 and 3). These cases illustrate variability in extra-skeletal manifestations, complications, and prognosis. In our patients with TRPV4-related disorders, the co-occurrence of neurological symptoms and skeletal abnormalities suggests a clinically heterogeneous spectrum consistent with a single disease rather than distinct entities. A comprehensive, multidisciplinary approach is essential to optimize management and improve the quality of life for patients.

Transient receptor potential vanilloid 4 (TRPV4) is a mechanosensitive ion channel highly expressed in chondrocytes that supports cartilage development and homeostasis. Mutations in the channel can cause skeletal dysplasias, including the gain-of-function mutations V620I and T89I, which lead to brachyolmia and metatropic dysplasia, respectively. These mutations suppress hypertrophic differentiation, but the mechanisms by which they alter chondrocyte response to mechanical load remain to be elucidated. To determine the effect of these mutations on chondrocyte mechanotransduction, tissue-engineered cartilage was derived from differentiated clustered regularly interspaced short palindromic repeats (CRISPR)-edited human-induced pluripotent stem cells (hiPSCs) harboring the moderate V620I or severe T89I TRPV4 mutations. Wild-type and mutant tissue-engineered hiPSC-derived cartilage contructs were subjected to compressive mechanical loading at physiological levels, and transcriptomic signatures were assessed by RNA-sequencing. Our results demonstrate that the V620I and T89I mutations diminish the mechanoresponsiveness of chondrocytes, as evidenced by reduced gene expression downstream of TRPV4 activation, including those involved in endochondral ossification. Changes in the expression of genes involved in extracellular matrix production and organization were found to contribute toward the phenotype in V620I mutant chondrocytes, whereas dysregulated retinoic acid signaling was linked to T89I, and disrupted proliferation was common to both. Our findings suggest that dysfunctional mechanotransduction due to V620I and T89I mutations in TRPV4 contribute to the developmental phenotypes, supporting TRPV4 modulation as a potential pharmacologic target.NEW & NOTEWORTHY Gain-of-function mutations in TRPV4, a mechano- and osmosensitive ion channel, are linked to skeletal dysplasias, but their effects on chondrocyte mechanotransduction remain unknown. Using human iPSCs harboring skeletal dysplasia-causing mutations, we developed and mechanically loaded tissue-engineered cartilage. Our findings show that V620I and T89I mutations reduce chondrocyte mechanoresponsiveness, evidenced by decreased gene expression downstream of TRPV4 activation, providing insight into TRPV4-related skeletal disorders and potential pharmacological targets.

To observe the natural history of the disease and the radiographic evolution of growth and development in patients with metatropic dysplasia (MD) and to complement the spectrum of mutations in the transient receptor potential vanilloid 4 (TRPV4) gene and the spectrum of MD phenotypes. We report a patient with MD caused by a novel missense mutation in TRPV4, who possessed a mixed phenotype of both abnormal skeletal development and peripheral neuropathy. From 3 months to the age of 7 years, we observed the patient's natural history and the imaging evolution of the patient's growth and development. The diagnosis of MD based on growth and developmental history, clinical presentation, imaging and mutation analysis of the TRPV4 gene. She underwent posterior spinal osteotomy (T10, vertebral column resection), lateral kyphosis correction, internal fixation (T6-L3), and implant fusion. Surgical intervention can effectively delay the course of the disease. Sequencing analysis and family validation of the patient's whole exon gene confirmed for the first time that the mutation in exon 11 of the TRPV4 gene was a heterozygous missense mutation (c.1811T > A) resulting in the mutation of isoleucine at position 604 to asparagine (p. I604N). This study complements the spectrum of mutations in the TRPV4 gene and the spectrum of MD phenotypes and provides a reference for prenatal diagnosis, genetic counseling, mechanistic studies, and development of symptomatic treatment for this type of disease.