Rhizomelic limb shortness and abnormal facies: short stature syndrome sharing some manifestations with robinow syndrome

In children, short stature and disproportionate skeletal growth are associated with many syndromes and these syndromes have characteristic radiological changes which help in their diagnosis. However, many of them have no well-defined diagnostic criteria, and thus overlap between apparently distinct syndromes is common. Here, we report a child with characteristic features seen distinct from any other dwarfing syndrome known to us with some of the features similar to Robinow syndrome. Newborn had a broad and prominent forehead, mid-face hypoplasia, hypertelorism, flat nasal bridge, upturned nose, elongated philtrum, protruding tongue, single crease in the left hand, widely spaced nipple, brachydactyly in lower limbs, and disproportionately short rhizomelic upper and lower limbs. Based on these features, a diagnosis of Robinow syndrome was made. The case was the first of his kind admitted to our institute. The diagnosis was made clinically after follow-up.

Structure and function of the ROR2 cysteine-rich domain in vertebrate noncanonical WNT5A signaling

The receptor tyrosine kinase ROR2 mediates noncanonical WNT5A signaling to orchestrate tissue morphogenetic processes, and dysfunction of the pathway causes Robinow syndrome, Brachydactyly B and metastatic diseases. The domain(s) and mechanisms required for ROR2 function, however, remain unclear. We solved the crystal structure of the extracellular cysteine rich (CRD) and Kringle (Kr) domains of ROR2 and found that, unlike other CRDs, the ROR2 CRD lacks the signature hydrophobic pocket that binds lipids/lipid-modified proteins, such as WNTs, suggesting a novel mechanism of receptor action. Functionally, we showed that the ROR2 CRD, but not other domains, is required and minimally sufficient to promote WNT5A signaling, and Robinow mutations in the CRD and the adjacent Kr alter ROR2 function. Moreover, we demonstrated that the activity of the ROR2 CRD requires Frizzled receptors. Thus, ROR2 acts via its CRD to potentiate the function of a receptor supercomplex that includes Frizzleds to transduce WNT5A signals.

OP0200 BLOCKING ROR2 IMPROVES CARTILAGE INTEGRITY AND PROVIDES PAIN RELIEF IN OSTEOARTHRITIS

Background:Osteoarthritis (OA) is the leading cause of chronic disability worldwide, affecting 12% of the population, and yet we still do not have a disease-modifying treatment. Cartilage breakdown is the hallmark of OA, and patients suffer from pain and loss of joint function/independence, severely affecting quality of life. Therefore, there is a huge unmet clinical need.Receptor tyrosine kinase–like orphan receptor 2 (ROR2) is a non-canonical WNT receptor that regulates the planar cell polarity pathway, controlling limb outgrowth during development. During skeletal development, chondrocytes require ROR2 to undergo hypertrophy throughout the process of endochondral bone formation1. Loss of function mutations in humans causes Recessive Robinow Syndrome, leading to limb shortening and brachydactyly2,3.Although absent from healthy adult articular cartilage, our initial studies identified high expression levels of ROR2 in chondrocytes from patients with OA, suggesting a role in the disease processObjectives:To test the potential of ROR2 blockade as a disease-modifying treatment for OA.Methods:Human cartilage organoid model in nude mice, menisco-ligament injury (MLI) model of OA in mice, behavioural studies, in vitro studies in cells.Results:ROR2/WNT5A signaling was increased in osteoarthritic cartilage. Blocking ROR2 was sufficient to induce articular chondrogenesis and suppress expression of aggrecanases in a mesenchymal stem cell line, and to support cartilage formation in a human cartilage organoid model in nude mice using primary chondrocytes from patients with OA.In the MLI model of OA, blocking ROR2 in therapeutic regime using atelocollagen-conjugated siRNA resulted in reduced cartilage destruction and in rapid and sustained pain relief. Due to the limited expression pattern of ROR2 in adulthood, no systemic or local toxicity were expected, nor were any observed4.With the current technology, ROR2 blockade requires intra-articular (IA) injections of siRNA conjugated to atelocollagen every 5 days. Preliminary efficacy data of potentially longer-acting ROR2 blockers are promising.The mechanism of action of ROR2 blockade was independent of modulation of canonical WNT signaling.ROR2/WNT5A promoted nuclear localization of YAP, which required both Rho and G-proteins. YAP signaling downstream of ROR2 also required Rho, but not G-proteins. YAP and TEAD inhibition was required, but not sufficient, for the chondrogenic effect of blocking ROR2. Therefore, additional, yet unknown mechanisms must be involved downstream of ROR2.Conclusion:ROR2 blockade has potential as a disease-modifying treatment for OA, resulting in cartilage protection and rapid and sustained pain relief in a murine model. This will be crucial for clinical success of any treatment for OA and promote patient compliance.Our current siRNA-atelocollagen based technology requires IA injections too frequently to be acceptable for patients. We are developing ROR2 blockade which can be administered systemically or IA not more often than every 3 months - work funded by FOREUM.References:[1]DeChiara, T. M. et al. Ror2, encoding a receptor-like tyrosine kinase, is required for cartilage and growth plate development. Nat. Genet.24, 271–4 (2000).[2]Bokhoven, H. Van, Celli, J. & Kayserili, H. Mutation of the gene encoding the ROR2 tyrosine kinase causes autosomal recessive Robinow syndrome. Nature25, 423–426 (2000).[3]Afzal, A., Rajab, A., Fenske, C. & Oldridge, M. Recessive Robinow syndrome, allelic to dominant brachydactyly type B, is caused by mutation of ROR2. Nature25, 419–422 (2000).[4]Thorup, A.-S. et al. ROR2 blockade as a therapy for osteoarthritis. Sci. Transl. Med.12, eaax3063 (2020).Acknowledgements:We gratefully acknowledge funding support of this work by the Medical College of St Bartholomew’s Hospital Trust, the William Harvey Research Foundation, FOREUM foundation for research in rheumatology (1016807), the MRC (MR/L022893/1, MR/N010973/1, MR/P026362/1, MR/K013076/1), Versus Arthritis (21515, 20886, 21621, 20859), and the DFG Emmy-Noether program (BE4328/5-1).Disclosure of Interests:Anne-Sophie Thorup: None declared, Danielle Strachan: None declared, Sara Caxaria: None declared, Blandine Poulet: None declared, Bethan Thomas: None declared, Suzanne Eldridge: None declared, Giovanna Nalesso: None declared, James Whiteford: None declared, Costantino Pitzalis: None declared, Thomas Aigner: None declared, Roger Corder: None declared, Jessica Bertrand: None declared, Francesco Dell’Accio Consultant of: Samumed and UCB

Canine DVL2 variant contributes to brachycephalic phenotype and caudal vertebral anomalies

A frameshift deletion variant in the Wnt pathway gene dishevelled 2 (DVL2) is associated with a truncated, kinked tail (“screw tail”) in English Bulldogs, French Bulldogs and Boston Terriers. These breeds are also characterized by distinctive morphological traits, including a wide head, flat face and short-limbed dwarfism, which are characteristic of Robinow syndrome in humans, caused by defects in genes such as DVL1 and DVL3. Based on these phenotypic and genetic similarities, it has previously been hypothesized that the canine DVL2 variant results in a syndromic phenotype called the Robinow-like syndrome. In our study, we investigated the distribution of the DVL2 variant in 1954 dogs from 15 breeds, identifying breeds with allele variation and enabling the dissection of the genotype–phenotype correlation for the first time. With CT examinations in American Staffordshire Terriers, we confirmed that the DVL2 allele is associated with caudal vertebral malformations and a brachycephalic phenotype. We also hypothesize that the variant may be linked to additional health conditions, including brachycephalic obstructive airway syndrome and congenital heart defects. Altogether, our study strengthens the role of DVL2 as one of the contributors to the “bulldog type” morphology and features on the spectrum of human Robinow syndrome.