Autoinflammatory phenotypes in Aicardi-Goutières syndrome with interferon upregulation and serological autoimmune features

Overlapping Aicardi-Goutières and Singleton-Merten syndromes with a heterozygous gain-of-function mutation in IFIH1 mimicking juvenile idiopathic arthritis

Aicardi-Goutières syndrome (AGS) and Singleton-Merten syndrome (SMS) are associated with heterozygous gain-of-function mutations in the interferon induced with helicase C domain 1 (IFIH1) gene. Recent reports describe patients exhibiting overlapping clinical features of AGS and SMS, along with marked type I interferon (IFN) overproduction. However, the clinical characteristics and optimal treatment strategies remain unclear. Herein, we present a patient with overlapping clinical features of AGS and SMS who was initially misdiagnosed with juvenile idiopathic arthritis. Surgical soft tissue release of the hip and knee joints improved joint deformities and spastic paraparesis. Baricitinib effectively treated refractory chilblains and skin ulcers while reducing IFN-stimulated gene overexpression in peripheral blood. These findings indicate that baricitinib may be a safe and effective treatment for AGS-SMS overlap, and surgical intervention may be a viable option for refractory joint deformities with spastic paraparesis.

Retroelement-derived RNA and its role in the brain

Comprising ~40% of the human genome, retroelements are mobile genetic elements which are transcribed into RNA, then reverse-transcribed into DNA and inserted into a new site in the genome. Retroelements are referred to as "genetic parasites", residing among host genes and relying on host machinery for transcription and evolutionary propagation. The healthy brain has the highest expression of retroelement-derived sequences compared to other somatic tissue, which leads to the question: how does retroelement-derived RNA influence human traits and cellular states? While the functional importance of upregulating retroelement expression in the brain is an active area of research, RNA species derived from retroelements influence both self- and host gene expression by contributing to chromatin remodeling, alternative splicing, somatic mosaicism and translational repression. Here, we review the emerging evidence that the functional importance of RNA derived from retroelements is multifaceted. Retroelements can influence organismal states through the seeding of epigenetic states in chromatin, the production of structured RNA and even catalytically active ribozymes, the generation of cytoplasmic ssDNA and RNA/DNA hybrids, the production of viral-like proteins, and the generation of somatic mutations. Comparative sequencing suggests that retroelements can contribute to intraspecies variation through these mechanisms to alter transcript identity and abundance. In humans, an increasing number of neurodevelopmental and neurodegenerative conditions are associated with dysregulated retroelements, including Aicardi-Goutieres syndrome (AGS), Rett syndrome (RTT), Amyotrophic Lateral Sclerosis (ALS), Alzheimer's disease (AD), multiple sclerosis (MS), schizophrenia (SZ), and aging. Taken together, these concepts suggest a larger functional role for RNA derived from retroelements. This review aims to define retroelement-derived RNA, discuss how it impacts the mammalian genome, as well as summarize data supporting phenotypic consequences of this unique RNA subset in the brain.