In humans, mutations in the FAM20C gene are responsible for highly lethal Raine syndrome, a neonatal osteosclerotic bone dysplasia (OMIM #259775), characterised by craniofacial anomalies, osteosclerosis and variable hypophosphataemia leading to dental and bone hypomineralisation. Here, FAM20C is linked to lethal osteosclerotic bone dysplasia.