The heterozygous IFIH1 missense mutations underlying several autosomal dominant autoimmune disorders, namely SLE, AGS and SMS, enhance interferon beta induction by MDA5, opposed to the IFIH1 nonsense mutation of patient II:1 which can be considered recessive (heterozygous carriers – the parents and the patient’s sister – are healthy). The gene discussed is IFNB1; the disease is systemic lupus erythematosus.