A gain-of-function mutation of the chondrocyte-specific microRNA, miR-140-5p, encoded by the MIR140 gene, causes spondyloepiphyseal dysplasia, Nishimura type (SEDN, also known as SED, MIR140 type; MIM, 611894). This evidence concerns the gene MIR140 and spondyloepiphyseal dysplasia.