C1S and Ehlers-Danlos syndrome: Finally, the periodontal form of Ehlers-Danlos syndrome (pEDS), characterised by periodontitis and gingival recessions but also skin abnormalities such as easy bruising, fragility and abnormal collagen fibrils, was recently shown to be caused by mutations in the complement proteases C1r and C1s, though the underlying molecular mechanisms are unknown25.