A novel pathogenic variant p.Asp797Val in IFIH1 in a Japanese boy with overlapping Singleton‐Merten syndrome and Aicardi‐Goutières syndrome

Pathogenic‐activating variants of interferon induced with Helicase C domain 1 (IFIH1) cause Singleton‐Merten (S‐M) syndrome, which accompanies acro‐osteolysis, loss of permanent teeth, and aortic calcification, as well as causing Aicardi‐Goutières (A‐G) syndrome, which shows progressive encephalopathy, spastic paraplegia, and calcification of basal ganglia. Recently, patients with overlapping syndromes presenting with features of S‐M syndrome and A‐G syndrome were reported. However, progression of clinical features of this condition has not been fully understood. We report a Japanese boy with a novel pathogenic IFIH1 variant who presented with clinical features of S‐M syndrome and A‐G syndrome.