TREX1 and systemic lupus erythematosus: AD defects in the nuclease TREX1 represent the most common cause of monogenic lupus with a frequency of 0.2–2 % in the adult SLE population [44–46] and have been linked to a particular form of SLE presenting with skin lesions of the extremities induced by cold exposure, called chilblains (CHBL1, OMIM610448) [47–49].