Hemizygous missense variants in the X-linked BGN gene, encoding the extracellular matrix protein biglycan, cause spondyloepimetaphyseal dysplasia (SEMD, biglycan type), which is clinically characterized by short stature, brachydactyly and osteoarthritis. The gene discussed is PSMB5; the disease is spondyloepimetaphyseal dysplasia, matrilin-3 type.