WARS2 mutations cause dopa-responsive early-onset parkinsonism and progressive myoclonus ataxia

Compound Heterozygous WARS2 Variants Including a Hypomorphic Allele Cause a Milder Phenotype of Complex Dopa Responsive Dystonia: Case Report and Review of the Literature

Biallelic WARS2 pathogenic variants responsible for partial defect in aminoacylation, have recently been reported in subjects presenting with late-onset phenotypes combining dopa-responsive early-onset dystonia parkinsonism with altered DaTSCAN and progressive myoclonus ataxia. Here, we present the case of a 39-year-old male with childhood-onset progressive dopa-responsive dystonia parkinsonism, prominent psychiatric features and ataxia whose genome sequencing identified a p.(Arg36Ter) nonsense variant and a hypomorphic p.(Trp13Gly) missense variant, allowing the diagnosis of WARS2-related disease. The p.(Trp13Gly) missense variant has previously been reported in individuals with less severe phenotypes than those carrying biallelic WARS2 loss-of-function variants. Among these individuals, two subjects had similar genetic backgrounds and almost identical clinical history to our patient. Our report brings additional proof that the p.(Trp13Gly) variant acts as a hypomorphic allele, offering insight on a genotype-phenotype correlation in WARS2-related disorders.

Pseudorabies virus manipulates mitochondrial tryptophanyl-tRNA synthetase 2 for viral replication

The pseudorabies virus (PRV) is identified as a double-helical DNA virus responsible for causing Aujeszky's disease, which results in considerable economic impacts globally. The enzyme tryptophanyl-tRNA synthetase 2 (WARS2), a mitochondrial protein involved in protein synthesis, is recognized for its broad expression and vital role in the translation process. The findings of our study showed an increase in both mRNA and protein levels of WARS2 following PRV infection in both cell cultures and animal models. Suppressing WARS2 expression via RNA interference in PK-15 ​cells led to a reduction in PRV infection rates, whereas enhancing WARS2 expression resulted in increased infection rates. Furthermore, the activation of WARS2 in response to PRV was found to be reliant on the cGAS/STING/TBK1/IRF3 signaling pathway and the interferon-alpha receptor-1, highlighting its regulation via the type I interferon signaling pathway. Further analysis revealed that reducing WARS2 levels hindered PRV's ability to promote protein and lipid synthesis. Our research provides novel evidence that WARS2 facilitates PRV infection through its management of protein and lipid levels, presenting new avenues for developing preventative and therapeutic measures against PRV infections.

The integrated stress response pathway and neuromodulator signaling in the brain: lessons learned from dystonia

The integrated stress response (ISR) is a highly conserved biochemical pathway involved in maintaining proteostasis and cell health in the face of diverse stressors. In this Review, we discuss a relatively noncanonical role for the ISR in neuromodulatory neurons and its implications for synaptic plasticity, learning, and memory. Beyond its roles in stress response, the ISR has been extensively studied in the brain, where it potently influences learning and memory, and in the process of synaptic plasticity, which is a substrate for adaptive behavior. Recent findings demonstrate that some neuromodulatory neuron types engage the ISR in an "always-on" mode, rather than the more canonical "on-demand" response to transient perturbations. Atypical demand for the ISR in neuromodulatory neurons introduces an additional mechanism to consider when investigating ISR effects on synaptic plasticity, learning, and memory. This basic science discovery emerged from a consideration of how the ISR might be contributing to human disease. To highlight how, in scientific discovery, the route from starting point to outcomes can often be circuitous and full of surprise, we begin by describing our group's initial introduction to the ISR, which arose from a desire to understand causes for a rare movement disorder, dystonia. Ultimately, the unexpected connection led to a deeper understanding of its fundamental role in the biology of neuromodulatory neurons, learning, and memory.

Next-generation sequencing and bioinformatics in rare movement disorders

The ability to sequence entire exomes and genomes has revolutionized molecular testing in rare movement disorders, and genomic sequencing is becoming an integral part of routine diagnostic workflows for these heterogeneous conditions. However, interpretation of the extensive genomic variant information that is being generated presents substantial challenges. In this Perspective, we outline multidimensional strategies for genetic diagnosis in patients with rare movement disorders. We examine bioinformatics tools and computational metrics that have been developed to facilitate accurate prioritization of disease-causing variants. Additionally, we highlight community-driven data-sharing and case-matchmaking platforms, which are designed to foster the discovery of new genotype-phenotype relationships. Finally, we consider how multiomic data integration might optimize diagnostic success by combining genomic, epigenetic, transcriptomic and/or proteomic profiling to enable a more holistic evaluation of variant effects. Together, the approaches that we discuss offer pathways to the improved understanding of the genetic basis of rare movement disorders.

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

The Expanding Phenotypical Spectrum of WARS2-Related Disorder: Four Novel Cases with a Common Recurrent Variant

Biallelic variants in the mitochondrial form of the tryptophanyl-tRNA synthetases (WARS2) can cause a neurodevelopmental disorder with movement disorders including early-onset tremor-parkinsonism syndrome. Here, we describe four new patients, who all presented at a young age with a tremor-parkinsonism syndrome and responded well to levodopa. All patients carry the same recurrent, hypomorphic missense variant (NM_015836.4: c.37T>G; p.Trp13Gly) either together with a previously described truncating variant (NM_015836.4: c.797Cdel; p.Pro266ArgfsTer10), a novel truncating variant (NM_015836.4: c.346C>T; p.Gln116Ter), a novel canonical splice site variant (NM_015836.4: c.349-1G>A), or a novel missense variant (NM_015836.4: c.475A>C, p.Thr159Pro). We investigated the mitochondrial function in patients and found increased levels of mitochondrially encoded cytochrome C Oxidase II as part of the mitochondrial respiratory chain as well as decreased mitochondrial integrity and branching. Finally, we conducted a literature review and here summarize the broad phenotypical spectrum of reported WARS2-related disorders. In conclusion, WARS2-related disorders are diagnostically challenging diseases due to the broad phenotypic spectrum and the disease relevance of a relatively common missense change that is often filtered out in a diagnostic setting since it occurs in ~0.5% of the general European population.

The Role of Nuclear-Encoded Mitochondrial tRNA Charging Enzymes in Human Inherited Disease

Aminoacyl-tRNA synthetases (ARSs) are highly conserved essential enzymes that charge tRNA with cognate amino acids-the first step of protein synthesis. Of the 37 nuclear-encoded human ARS genes, 17 encode enzymes are exclusively targeted to the mitochondria (mt-ARSs). Mutations in nuclear mt-ARS genes are associated with rare, recessive human diseases with a broad range of clinical phenotypes. While the hypothesized disease mechanism is a loss-of-function effect, there is significant clinical heterogeneity among patients that have mutations in different mt-ARS genes and also among patients that have mutations in the same mt-ARS gene. This observation suggests that additional factors are involved in disease etiology. In this review, we present our current understanding of diseases caused by mutations in the genes encoding mt-ARSs and propose explanations for the observed clinical heterogeneity.

Mitochondrial protein synthesis and the bioenergetic cost of neurodevelopment

The human brain consumes five orders of magnitude more energy than the sun by unit of mass and time. This staggering bioenergetic cost serves mostly synaptic transmission and actin cytoskeleton dynamics. The peak of both brain bioenergetic demands and the age of onset for neurodevelopmental disorders is approximately 5 years of age. This correlation suggests that defects in the machinery that provides cellular energy would be causative and/or consequence of neurodevelopmental disorders. We explore this hypothesis from the perspective of the machinery required for the synthesis of the electron transport chain, an ATP-producing and NADH-consuming enzymatic cascade. The electron transport chain is constituted by nuclear- and mitochondrial-genome-encoded subunits. These subunits are synthesized by the 80S and the 55S ribosomes, which are segregated to the cytoplasm and the mitochondrial matrix, correspondingly. Mitochondrial protein synthesis by the 55S ribosome is the rate-limiting step in the synthesis of electron transport chain components, suggesting that mitochondrial protein synthesis is a bottleneck for tissues with high bionergetic demands. We discuss genetic defects in the human nuclear and mitochondrial genomes that affect these protein synthesis machineries and cause a phenotypic spectrum spanning autism spectrum disorders to neurodegeneration during neurodevelopment. We propose that dysregulated mitochondrial protein synthesis is a chief, yet understudied, causative mechanism of neurodevelopmental and behavioral disorders.