Adenosine deaminases acting on RNA (ADARs) catalyze the hydrolytic deamination of adenosine to inosine in double-stranded RNA (dsRNA) and thereby potentially alter the information content and structure of cellular RNAs. Notably, although the overwhelming majority of such editing events occur in transcripts derived from Alu repeat elements, the biological function of non-coding RNA editing remains uncertain. Here, we show that mutations in ADAR1 (also known as ADAR) cause the autoimmune disorder Aicardi-Goutières syndrome (AGS). As in Adar1-null mice, the human disease state is associated with upregulation of interferon-stimulated genes, indicating a possible role for ADAR1 as a suppressor of type I interferon signaling. Considering recent insights derived from the study of other AGS-related proteins, we speculate that ADAR1 may limit the cytoplasmic accumulation of the dsRNA generated from genomic repetitive elements.

Summary Background Aicardi-Goutières syndrome (AGS) is an inflammatory disorder caused by mutations in any of six genes (TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, and ADAR). The disease is severe and effective treatments are urgently needed. We investigated the status of interferon-related biomarkers in patients with AGS with a view to future use in diagnosis and clinical trials. Methods In this case-control study, samples were collected prospectively from patients with mutation-proven AGS. The expression of six interferon-stimulated genes (ISGs) was measured by quantitative PCR, and the median fold change, when compared with the median of healthy controls, was used to create an interferon score for each patient. Scores higher than the mean of controls plus two SD (>2·466) were designated as positive. Additionally, we collated historical data for interferon activity, measured with a viral cytopathic assay, in CSF and serum from mutation-positive patients with AGS. We also undertook neutralisation assays of interferon activity in serum, and looked for the presence of autoantibodies against a panel of interferon proteins. Findings 74 (90%) of 82 patients had a positive interferon score (median 12·90, IQR 6·14–20·41) compared with two (7%) of 29 controls (median 0·93, IQR 0·57–1·30). Of the eight patients with a negative interferon score, seven had mutations in RNASEH2B (seven [27%] of all 26 patients with mutations in this gene). Repeat sampling in 16 patients was consistent for the presence or absence of an interferon signature on 39 of 41 occasions. Interferon activity (tested in 147 patients) was negatively correlated with age (CSF, r=−0·604; serum, r=−0·289), and was higher in CSF than in serum in 104 of 136 paired samples. Neutralisation assays suggested that measurable antiviral activity was related to interferon α production. We did not record significantly increased concentrations of autoantibodies to interferon subtypes in patients with AGS, or an association between the presence of autoantibodies and interferon score or serum interferon activity. Interpretation AGS is consistently associated with an interferon signature, which is apparently sustained over time and can thus be used to differentiate patients with AGS from controls. If future studies show that interferon status is a reactive biomarker, the measurement of an interferon score might prove useful in the assessment of treatment efficacy in clinical trials. Funding European Union’s Seventh Framework Programme; European Research Council.

We report on ten individuals with a fatal infantile encephalopathy and/or pulmonary hypertension, leading to death before the age of 15 months. Hyperglycinemia and lactic acidosis were common findings. Glycine cleavage system and pyruvate dehydrogenase complex (PDHC) activities were low. Homozygosity mapping revealed a perfectly overlapping homozygous region of 1.24 Mb corresponding to chromosome 2 and led to the identification of a homozygous missense mutation (c.622G > T) in NFU1, which encodes a conserved protein suggested to participate in Fe-S cluster biogenesis. Nine individuals were homozygous for this mutation, whereas one was compound heterozygous for this and a splice-site (c.545 + 5G > A) mutation. The biochemical phenotype suggested an impaired activity of the Fe-S enzyme lipoic acid synthase (LAS). Direct measurement of protein-bound lipoic acid in individual tissues indeed showed marked decreases. Upon depletion of NFU1 by RNA interference in human cell culture, LAS and, in turn, PDHC activities were largely diminished. In addition, the amount of succinate dehydrogenase, but no other Fe-S proteins, was decreased. In contrast, depletion of the general Fe-S scaffold protein ISCU severely affected assembly of all tested Fe-S proteins, suggesting that NFU1 performs a specific function in mitochondrial Fe-S cluster maturation. Similar biochemical effects were observed in Saccharomyces cerevisiae upon deletion of NFU1, resulting in lower lipoylation and SDH activity. Importantly, yeast Nfu1 protein carrying the individuals' missense mutation was functionally impaired. We conclude that NFU1 functions as a late-acting maturation factor for a subset of mitochondrial Fe-S proteins.

BackgroundIsovaleric aciduria (IVA), propionic aciduria (PA) and methylmalonic aciduria (MMA) are inherited organic acidurias (OAs) in which impaired organic acid metabolism induces hyperammonaemia arising partly from secondary deficiency of N-acetylglutamate (NAG) synthase. Rapid reduction in plasma ammonia is required to prevent neurological complications. This retrospective, multicentre, open-label, uncontrolled, phase IIIb study evaluated the efficacy and safety of carglumic acid, a synthetic structural analogue of NAG, for treating hyperammonaemia during OA decompensation.MethodsEligible patients had confirmed OA and hyperammonaemia (plasma NH3 > 60 μmol/L) in ≥1 decompensation episode treated with carglumic acid (dose discretionary, mean (SD) first dose 96.3 (73.8) mg/kg). The primary outcome was change in plasma ammonia from baseline to endpoint (last available ammonia measurement at ≤18 hours after the last carglumic acid administration, or on Day 15) for each episode. Secondary outcomes included clinical response and safety.ResultsThe efficacy population (received ≥1 dose of study drug and had post-baseline measurements) comprised 41 patients (MMA: 21, PA: 16, IVA: 4) with 48 decompensation episodes (MMA: 25, PA: 19, IVA: 4). Mean baseline plasma ammonia concentration was 468.3 (±365.3) μmol/L in neonates (29 episodes) and 171.3 (±75.7) μmol/L in non-neonates (19 episodes). At endpoint the mean plasma NH3 concentration was 60.7 (±36.5) μmol/L in neonates and 55.2 (±21.8) μmol/L in non-neonates. Median time to normalise ammonaemia was 38.4 hours in neonates vs 28.3 hours in non-neonates and was similar between OA subgroups (MMA: 37.5 hours, PA: 36.0 hours, IVA: 40.5 hours). Median time to ammonia normalisation was 1.5 and 1.6 days in patients receiving and not receiving concomitant scavenger therapy, respectively. Although patients receiving carglumic acid with scavengers had a greater reduction in plasma ammonia, the endpoint ammonia levels were similar with or without scavenger therapy. Clinical symptoms improved with therapy. Twenty-five of 57 patients in the safety population (67 episodes) experienced AEs, most of which were not drug-related. Overall, carglumic acid seems to have a good safety profile for treating hyperammonaemia during OA decompensation.ConclusionCarglumic acid when used with or without ammonia scavengers, is an effective treatment for restoration of normal plasma ammonia concentrations in hyperammonaemic episodes in OA patients.

Familial hemiplegic migraine (FHM) is a rare type of migraine with aura. Mutations in three genes have been described in FHM patients: CACNA1A (FHM1), ATP1A2 (FHM2) and SCN1A (FHM3). We screened 27 Spanish patients with hemiplegic migraine (HM), basilar-type migraine or childhood periodic syndromes (CPS) for mutations in these three genes. Two novel CACNA1A variants, p.Val581Met and p.Tyr1245Cys, and a previously annotated change, p.Cys1534Ser, were identified in individuals with HM, although they have not yet been proven to be pathogenic. Interestingly, p.Tyr1245Cys was detected in a patient displaying a changing, age-specific phenotype that began as benign paroxysmal torticollis of infancy, evolving into benign paroxysmal vertigo of childhood and later becoming HM. This is the first instance of a specific non-synonymous base change being described in a subject affected with CPS. The fact that the molecular screen identified non-synonymous changes in < 15% of our HM patients further stresses the genetic heterogeneity underlying the presumably monogenic forms of migraine.

Inherited Metabolic Diseases (IMDs) are rare diseases caused by genetic defects in biochemical pathways. Earlier diagnosis and advances in treatment have improved the life expectancy of IMD patients over the last decades, with the majority of patients now surviving beyond the age of 20. This has created a new challenge: as they grow up, the care of IMD patients' needs to be transferred from metabolic pediatricians to metabolic physicians specialized in treating adults, through a process called “transition.” The purpose of this study was to assess how this transition is managed in Europe: a survey was sent to all 77 centers of the European Reference Network for Hereditary Metabolic Disorders (MetabERN) to collect information and to identify unmet needs regarding the transition process. Data was collected from 63/77 (81%) healthcare providers (HCPs) from 20 EU countries. Responders were mostly metabolic pediatricians; of these, only ~40% have received appropriate training in health issues of adolescent metabolic patients. In most centers (~67%) there is no designated transition coordinator. About 50% of centers provide a written individualized transition protocol, which is standardized in just ~20% of cases. In 77% of centers, pediatricians share a medical summary, transition letter and emergency plan with the adult team and the patient. According to our responders, 11% of patients remain under pediatric care throughout their life. The main challenges identified by HCPs in managing transition are lack of time and shortage of adult metabolic physician positions, while the implementations that are most required for a successful transition include: medical staff dedicated to transition, a transition coordinator, and specific metabolic training for adult physicians. Our study shows that the transition process of IMD patients in Europe is far from standardized and in most cases is inadequate or non-existent. A transition coordinator to facilitate collaboration between the pediatric and adult healthcare teams should be central to any transition program. Standardized operating procedures, together with adequate financial resources and specific training for adult physicians focused on IMDs are the key aspects that must be improved in the rare metabolic field to establish successful transition processes in Europe.

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Despite optimal medical treatment and strict low-protein diet, the prognosis of propionic acidemia (PA) patients is generally poor. We aim to report our experience with liver transplantation (LT) in the management of PA patients. Six patients with PA received a LT at a mean age of 5.2 years (1.3-7.5 years). The indications for LT were frequent metabolic decompensations in the first 4 patients and preventative in the last 2 patients. Two patients presented hepatic artery thromboses that were solved through an interventional radiologist approach. These patients showed a very high procoagulant state that was observed by thromboelastography. Arterial vasospasm without thrombus was observed in 2 patients during the LT surgery. In order to avoid hepatic artery thrombosis, an arterial conduit from the recipient aorta to the hepatic artery of the donor was used in the fifth patient. After LT, patients presented improvement in propionyl byproducts without complete normalization, but no decompensations have been observed. In conclusion, LT could be a good therapeutic option to improve the metabolic control and the quality of life of PA patients. Improved surgical strategies along with new techniques of interventional radiology allow us to perform the LT minimizing the complications derived from the higher risk of hepatic artery thrombosis.