Aicardi-Goutières syndrome (AGS) is an inflammatory disorder belonging to the 
recently characterized group of type I interferonopathies. The most consistently 
affected tissues in AGS are the central nervous system and skin, but various 
organ systems and tissues have been reported to be affected, pointing to the 
systemic nature of the disease. Here we describe a patient with AGS due to a 
homozygous p.Arg114His mutation in the TREX1 gene. The histologically proven 
inflammatory myopathy in our patient expands the range of clinical features of 
AGS. Histological signs of muscle biopsies in the proband, and in two other AGS 
patients described earlier, are similar to those seen in various autoimmune 
myositises and could be ascribed to inapproapriate IFN I activation. In view of 
signs of possible mitochondrial damage in AGS, we propose that mitochondrial DNA 
could be a trigger of autoimmune responses in AGS.