Monarch Disease Ontology entry MONDO_0009952 (radioulnar synostosis-developmental delay-hypotonia syndrome), also known as Der Kaloustian-McIntosh-Silver syndrome, is an extremely rare syndrome with synostosis described in about 4 patients to date with clinical manifestations including congenital unilateral radioulnar synostosis, generalized hypotonia, developmental delay, and dysmorphic facial features (long face, prominent nose and ears). Also known as: Der Kaloustian-McIntosh-Silver syndrome, radioulnar synostosis with developmental delay and hypotonia syndrome.