Variants in ATP5F1B are associated with dominantly inherited dystonia.

ATP5F1B is a subunit of the mitochondrial ATP synthase or complex V of the mitochondrial respiratory chain. Pathogenic variants in nuclear genes encoding assembly factors or structural subunits are associated with complex V deficiency, typically characterized by autosomal recessive inheritance and multisystem phenotypes. Movement disorders have been described in a subset of cases carrying autosomal dominant variants in structural subunits genes ATP5F1A and ATP5MC3. Here, we report the identification of two different ATP5F1B missense variants (c.1000A>C; p.Thr334Pro and c.1445T>C; p.Val482Ala) segregating with early-onset isolated dystonia in two families, both with autosomal dominant mode of inheritance and incomplete penetrance. Functional studies in mutant fibroblasts revealed no decrease of ATP5F1B protein amount but severe reduction of complex V activity and impaired mitochondrial membrane potential, suggesting a dominant-negative effect. In conclusion, our study describes a new candidate gene associated with isolated dystonia and confirms that heterozygous variants in genes encoding subunits of the mitochondrial ATP synthase may cause autosomal dominant isolated dystonia with incomplete penetrance, likely through a dominant-negative mechanism.

Genetics, sex, and gender.

This review aims to give an overview of what has been discovered so far and what still needs to be analyzed about how sex and gender affect the disease development. These two terms are often confused and indifferently used. In principle, the term "sex" refers to biological differences between males and females, specifically reproductive organs and their functions, while the term "gender" refers to the social context in which people live and which contributes to a subjective sexual identity, masculine or feminine. This dichotomy, however, is not so rigid and both sex and gender influence different aspects of human health, such as brain, health and aging and drug treatment and pharmacokinetics. In particular, we want to focus on genetic differences between men and women: indeed, the expression of the genes mapped on X chromosome or Y chromosome and all epigenetic interactions affect the diseases development. Finally, we will briefly outline sex and gender differences in clinical manifestations of three neurological diseases: Alzheimer's disease, Parkinson's disease, and obsessive compulsive disorder. In the era of personalized medicine, we must not forget the importance of gender medicine to promote personalized care for any kind of patients.

Harmonizing Genetic Testing for Parkinson's Disease: Results of the PARKNET Multicentric Study.

BACKGROUND AND OBJECTIVE: Early-onset Parkinson's disease (EOPD) commonly recognizes a genetic basis; thus, patients with EOPD are often addressed to diagnostic testing based on next-generation sequencing (NGS) of PD-associated multigene panels. However, NGS interpretation can be challenging in a diagnostic setting, and few studies have addressed this issue so far. METHODS: We retrospectively collected data from 648 patients with PD with age at onset younger than 55 years who underwent NGS of a minimal shared panel of 15 PD-related genes, as well as PD-multiplex ligation-dependent probe amplification in eight Italian diagnostic laboratories. Data included a minimal clinical dataset, the complete list of variants included in the diagnostic report, and final interpretation (positive/negative/inconclusive). Patients were further stratified based on age at onset ≤40 years (very EOPD, n = 157). All variants were reclassified according to the latest American College of Medical Genetics and Genomics criteria. For classification purposes, PD-associated GBA1 variants were considered diagnostic. RESULTS: In 186 of 648 (29%) patients, the diagnostic report listed at least one variant, and the outcome was considered diagnostic (positive) in 105 (16%). After reanalysis, diagnosis changed in 18 of 186 (10%) patients, with 5 shifting from inconclusive to positive and 13 former positive being reclassified as inconclusive. A definite diagnosis was eventually reached in 97 (15%) patients, of whom the majority carried GBA1 variants or, less frequently, biallelic PRKN variants. In 89 (14%) cases, the genetic report was inconclusive. CONCLUSIONS: This study attempts to harmonize reporting of PD genetic testing across several diagnostic labs and highlights current difficulties in interpreting genetic variants emerging from NGS-multigene panels, with relevant implications for counseling. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Protective Role of Tacrolimus, Deleterious Role of Age and Comorbidities in Liver Transplant Recipients With Covid-19: Results From the ELITA/ELTR Multi-center European Study.

BACKGROUND AND AIMS: Despite concerns that liver transplant (LT) recipients may be at increased risk of unfavorable outcomes from COVID-19 due the high prevalence of co-morbidities, immunosuppression and ageing, a detailed analysis of their effects in large studies is lacking. METHODS: Data from adult LT recipients with laboratory confirmed SARS-CoV2 infection were collected across Europe. All consecutive patients with symptoms were included in the analysis. RESULTS: Between March 1 and June 27, 2020, data from 243 adult symptomatic cases from 36 centers and 9 countries were collected. Thirty-nine (16%) were managed as outpatients while 204 (84%) required hospitalization including admission to the ICU (39 of 204, 19.1%). Forty-nine (20.2%) patients died after a median of 13.5 (10-23) days, respiratory failure was the major cause. After multivariable Cox regression analysis, age >70 (HR, 4.16; 95% CI, 1.78-9.73) had a negative effect and tacrolimus (TAC) use (HR, 0.55; 95% CI, 0.31-0.99) had a positive independent effect on survival. The role of co-morbidities was strongly influenced by the dominant effect of age where comorbidities increased with the increasing age of the recipients. In a second model excluding age, both diabetes (HR, 1.95; 95% CI, 1.06-3.58) and chronic kidney disease (HR, 1.97; 95% CI, 1.05-3.67) emerged as associated with death CONCLUSIONS: Twenty-five percent of patients requiring hospitalization for COVID-19 died, the risk being higher in patients older than 70 and with medical co-morbidities, such as impaired renal function and diabetes. Conversely, the use of TAC was associated with a better survival thus encouraging clinicians to keep TAC at the usual dose.

Location and allocation: Inequity of access to liver transplantation for patients with severe acute-on-chronic liver failure in Europe.

There is growing evidence that liver transplantation (LT) is the most effective treatment for acute-on-chronic liver failure grade-3 (ACLF-3). This study examines whether and how this evidence translates into practice by analyzing the variability in intensive care unit (ICU) admissions, listing strategies, and LT activity for patients with ACLF-3 across transplantation centers in Europe. Consecutive patients who were admitted to the ICU with ACLF-3, whether or not they were listed and/or transplanted with ACLF-3, between 2018 and 2019 were included across 20 transplantation centers. A total of 351 patients with ACLF-3 were included: 33 had been listed prior to developing ACLF-3 and 318 had not been listed at the time of admission to the ICU. There was no correlation between the number of unlisted patients with ACLF-3 admitted to the ICU and the number listed or transplanted while in ACLF-3 across centers. By contrast, there was a correlation between the number of patients listed and the number transplanted while in ACLF-3. About 21% of patients who were listed while in ACLF-3 died on the waiting list or were delisted. The percentage of LT for patients with ACLF-3 varied from 0% to 29% for those transplanted with decompensated cirrhosis across centers (average = 8%), with an I2 index of 68% (95% confidence interval, 49%-80%), showing substantial heterogeneity among centers. The 1-year survival for all patients with ACLF-3 was significantly higher in centers that listed and transplanted more patients with ACLF-3 (>10 patients) than in centers that listed and transplanted fewer: 36% versus 20%, respectively (p = 0.012). Patients with ACLF-3 face inequity of access to LT across Europe. Waitlisting strategies for patients with ACLF-3 influence their access to LT and, ultimately, their survival.

COVID-19 in liver transplant candidates: pretransplant and post-transplant outcomes - an ELITA/ELTR multicentre cohort study.

OBJECTIVE: Explore the impact of COVID-19 on patients on the waiting list for liver transplantation (LT) and on their post-LT course. DESIGN: Data from consecutive adult LT candidates with COVID-19 were collected across Europe in a dedicated registry and were analysed. RESULTS: From 21 February to 20 November 2020, 136 adult cases with laboratory-confirmed SARS-CoV-2 infection from 33 centres in 11 European countries were collected, with 113 having COVID-19. Thirty-seven (37/113, 32.7%) patients died after a median of 18 (10-30) days, with respiratory failure being the major cause (33/37, 89.2%). The 60-day mortality risk did not significantly change between first (35.3%, 95% CI 23.9% to 50.0%) and second (26.0%, 95% CI 16.2% to 40.2%) waves. Multivariable Cox regression analysis showed Laboratory Model for End-stage Liver Disease (Lab-MELD) score of ≥15 (Model for End-stage Liver Disease (MELD) score 15-19, HR 5.46, 95% CI 1.81 to 16.50; MELD score≥20, HR 5.24, 95% CI 1.77 to 15.55) and dyspnoea on presentation (HR 3.89, 95% CI 2.02 to 7.51) being the two negative independent factors for mortality. Twenty-six patients underwent an LT after a median time of 78.5 (IQR 44-102) days, and 25 (96%) were alive after a median follow-up of 118 days (IQR 31-170). CONCLUSIONS: Increased mortality in LT candidates with COVID-19 (32.7%), reaching 45% in those with decompensated cirrhosis (DC) and Lab-MELD score of ≥15, was observed, with no significant difference between first and second waves of the pandemic. Respiratory failure was the major cause of death. The dismal prognosis of patients with DC supports the adoption of strict preventative measures and the urgent testing of vaccination efficacy in this population. Prior SARS-CoV-2 symptomatic infection did not affect early post-transplant survival (96%).

Novel NDUFA12 variants are associated with isolated complex I defect and variable clinical manifestation.

Isolated biochemical deficiency of mitochondrial complex I is the most frequent signature among mitochondrial diseases and is associated with a wide variety of clinical symptoms. Leigh syndrome represents the most frequent neuroradiological finding in patients with complex I defect and more than 80 monogenic causes have been involved in the disease. In this report, we describe seven patients from four unrelated families harboring novel NDUFA12 variants, with six of them presenting with Leigh syndrome. Molecular genetic characterization was performed using next-generation sequencing combined with the Sanger method. Biochemical and protein studies were achieved by enzymatic activities, blue native gel electrophoresis, and western blot analysis. All patients displayed novel homozygous mutations in the NDUFA12 gene, leading to the virtual absence of the corresponding protein. Surprisingly, despite the fact that in none of the analyzed patients, NDUFA12 protein was detected, they present a different onset and clinical course of the disease. Our report expands the array of genetic alterations in NDUFA12 and underlines phenotype variability associated with NDUFA12 defect.

Expanding the genetic spectrum of primary familial brain calcification due to SLC2OA2 mutations: a case series.

Primary familial brain calcification (PFBC) is a neurological condition characterized by the presence of intracranial calcifications, mainly involving basal ganglia, thalamus, and dentate nuclei. So far, six genes have been linked to this condition: SLC20A2, PDGFRB, PDGFB, and XPR1 inherited as autosomal-dominant trait, while MYORG and JAM2 present a recessive pattern of inheritance. Patients mainly present with movement disorders, psychiatric disturbances, and cognitive decline or are completely asymptomatic and calcifications may represent an occasional finding. Here we present three variants in SLC20A2, two exonic and one intronic, which we found in patients with PFBC associated to three different clinical phenotypes. One variant is novel and two were already described as variants of uncertain significance. We confirm the pathogenicity of these three variants and suggest a broadening of the phenotypic spectrum associated with mutations in SLC20A2.

Liver transplantation for patients with acute-on-chronic liver failure (ACLF) in Europe: Results of the ELITA/EF-CLIF collaborative study (ECLIS).

BACKGROUND & AIMS: Liver transplantation (LT) has been proposed as an effective salvage therapy even for the sickest patients with acute-on-chronic liver failure (ACLF). This large collaborative study was designed to assess the current clinical practice and outcomes of patients with ACLF who are wait-listed for LT in Europe. METHODS: This was a retrospective study including 308 consecutive patients with ACLF, listed in 20 centres across 8 European countries, from January 2018 to June 2019. RESULTS: A total of 2,677 patients received a LT: 1,216 (45.4%) for decompensated cirrhosis. Of these, 234 (19.2%) had ACLF at LT: 58 (4.8%) had ACLF-1, 78 (6.4%) had ACLF-2, and 98 (8.1%) had ACLF-3. Wide variations were observed amongst countries: France and Germany had high rates of ACLF-2/3 (27-41%); Italy, Switzerland, Poland and the Netherlands had medium rates (9-15%); and the United Kingdom and Spain had low rates (3-5%) (p <0.0001). The 1-year probability of survival after LT for patients with ACLF was 81% (95% CI 74-87). Pre-LT arterial lactate levels >4 mmol/L (hazard ratio [HR] 3.14; 95% CI 1.37-7.19), recent infection from multidrug resistant organisms (HR 3.67; 95% CI 1.63-8.28), and renal replacement therapy (HR 2.74; 95% CI 1.37-5.51) were independent predictors of post-LT mortality. During the same period, 74 patients with ACLF died on the waiting list. In an intention-to-treat analysis, 1-year survival of patients with ACLF on the LT waiting list was 73% for ACLF-1 or -2 and 50% for ACLF-3. CONCLUSION: The results reveal wide variations in the listing of patients with ACLF in Europe despite favourable post-LT survival. Risk factors for mortality were identified, enabling a more precise prognostic assessment of patients with ACLF. LAY SUMMARY: Acute-on-chronic liver failure (ACLF) is a severe clinical condition for which liver transplantation is an effective therapeutic option. This study has demonstrated that in Europe, referral and access to liver transplantation (LT) for patients with ACLF needs to be harmonised to avoid inequities. Post-LT survival for patients with ACLF was >80% after 1 year and some factors have been identified to help select patients with favourable outcomes.

Regorafenib Efficacy After Sorafenib in Patients With Recurrent Hepatocellular Carcinoma After Liver Transplantation: A Retrospective Study.

Safety of regorafenib in hepatocellular carcinoma (HCC) recurrence after liver transplantation (LT) has been recently demonstrated. We aimed to assess the survival benefit of regorafenib compared with best supportive care (BSC) in LT patients after sorafenib discontinuation. This observational multicenter retrospective study included LT patients with HCC recurrence who discontinued first-line sorafenib. Group 1 comprised regorafenib-treated patients, whereas the control group was selected among patients treated with BSC due to unavailability of second-line options at the time of sorafenib discontinuation and who were sorafenib-tolerant progressors (group 2). Primary endpoint was overall survival (OS) of group 1 compared with group 2. Secondary endpoints were safety and OS of sequential treatment with sorafenib + regorafenib/BSC. Among 132 LT patients who discontinued sorafenib included in the study, 81 were sorafenib tolerant: 36 received regorafenib (group 1) and 45 (group 2) received BSC. Overall, 24 (67%) patients died in group 1 and 40 (89%) in group 2: the median OS was significantly longer in group 1 than in group 2 (13.1 versus 5.5 months; P < 0.01). Regorafenib treatment was an independent predictor of reduced mortality (hazard ratio, 0.37; 95% confidence interval [CI], 0.16-0.89; P = 0.02). Median treatment duration with regorafenib was 7.0 (95% CI, 5.5-8.5) months; regorafenib dose was reduced in 22 (61%) patients for adverse events and discontinued for tumor progression in 93% (n = 28). The median OS calculated from sorafenib start was 28.8 months (95% CI, 17.6-40.1) in group 1 versus 15.3 months (95% CI, 8.8-21.7) in group 2 (P < 0.01). Regorafenib is an effective second-line treatment after sorafenib in patients with HCC recurrence after LT.

Cost analysis of a long-term randomized controlled study in biliary duct-to-duct anastomotic stricture after liver transplantation.

Multiple plastic stent (MPS) for biliary anastomotic stricture (AS) after liver transplantation requires multiple procedures with consequent costs. To compare the success, adverse events and treatment-related costs of fully covered self-expandable metal stents (FCSEMS) versus MPS. Thirty liver transplant (LT) patients with clinically relevant naïve AS were prospectively randomized to FCSEMS or MPS, with stent numbers increased at 3-month intervals. Treatment costs per patient were calculated for endoscopic retrograde cholangiopancreatography (including all devices and stents) and overall hospital stay. Radiological success was achieved in 73% of FCSEMS (median indwelling period of 6 mos) and 93% of MPS patients (P = NS) (median period of 11 mos). AS recurrence occurred in 36% of FCSEMS and 7% of MPS patients (P = NS), and AS re-treatment was needed in 53% and 13% (P < 0.01), respectively, during follow-up of 60 (34-80) months. Stents migrated after 29% and 2.6% of FCSEMS and MPS procedures, respectively (P < 0.01). Including re-treatments, long-term clinical success was achieved in 28/30 (93%) patients. Overall treatment-related costs were similar between groups. In the subgroup of LT patients in clinical remission after first-line treatment, treatment costs were 41% lower per FCSEMS patient compared with MPS patients. FCSEMS did not perform better than MPS. FCSEMS migration increased the rate of re-treatment and costs.

COVID-19 in an international European liver transplant recipient cohort.

OBJECTIVE: Knowledge on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in liver transplant recipients is lacking, particularly in terms of severity of the disease. The aim of this study was to describe the demographic, baseline clinical characteristics and early outcomes of a European cohort of liver transplant recipients with SARS-CoV-2 infection. DESIGN: We conducted an international prospective study across Europe on liver transplant recipients with SARS-CoV-2 infection confirmed by microbiological assay during the first outbreak of COVID-19 pandemic. Baseline characteristics, clinical presentation, management of immunosuppressive therapy and outcomes were collected. RESULTS: 57 patients were included (70% male, median (IQR) age at diagnosis 65 (57-70) years). 21 (37%), 32 (56%) and 21 (37%) patients had one cardiovascular disease, arterial hypertension and diabetes mellitus, respectively. The most common symptoms were fever (79%), cough (55%), dyspnoea (46%), fatigue or myalgia (56%) and GI symptoms (33%). Immunosuppression was reduced in 22 recipients (37%) and discontinued in 4 (7%). With this regard, no impact on outcome was observed. Forty-one (72%) subjects were hospitalised and 11 (19%) developed acute respiratory distress syndrome. Overall, we estimated a case fatality rate of 12% (95% CI 5% to 24%), which increased to 17% (95% CI 7% to 32%) among hospitalised patients. Five out of the seven patients who died had a history of cancer. CONCLUSION: In this European multicentre prospective study of liver transplant recipients, COVID-19 was associated with an overall and in-hospital fatality rate of 12% (95% CI 5% to 24%) and 17% (95% CI 7% to 32%), respectively. A history of cancer was more frequent in patients with poorer outcome.

Efficacy and safety of device-assisted enteroscopy ERCP in liver transplantation: A systematic review and meta-analysis.

BACKGROUND: Enterobiliary anastomoses are the main source of complications after liver transplantation. An endoscopic approach combining device-assisted enteroscopy and ERCP (DAE-ERCP) is technically feasible in postsurgical anatomy. AIMS: This study aimed at assessing the efficacy, feasibility, and safety of DAE-ERCP in liver-transplanted patients (LT) and other subsets (non-LT). METHODS: A systematic review and meta-analysis of studies involving DAE procedures in LT patients (between January 2000 and May 2017) was conducted. The main endpoints were as follows: endoscopic, diagnostic, therapeutic, and overall success rates, complications, and the need for surgery. RESULTS: A total of 155 studies were retrieved, and 6 relevant trials were analyzed. Overall, 132 subjects (72 LT and 60 non-LT) undergoing 257 DAE-ERCP (135 and 122) were included. Complications were rare (4/257), and no deaths occurred. These are the pooled success rates among LT and non-LT patients: 80%-100% and 82%-95% (enteroscopic), 75%-100% and 89%-100% (diagnostic), 67%-100% and 92%-100% (therapeutic), and 60%-100% and 79%-83% (overall results). The requirement for surgery was similar in the two subgroups. CONCLUSION: In managing biliary complications, the high diagnostic and therapeutic success rates of DAE-ERCP combined with its safety and feasibility encourage its application as a first-line approach to transplanted patients.

Mutations in ELAC2 associated with hypertrophic cardiomyopathy impair mitochondrial tRNA 3'-end processing.

Mutations in either the mitochondrial or nuclear genomes are associated with a diverse group of human disorders characterized by impaired mitochondrial respiration. Within this group, an increasing number of mutations have been identified in nuclear genes involved in mitochondrial RNA metabolism, including ELAC2. The ELAC2 gene codes for the mitochondrial RNase Z, responsible for endonucleolytic cleavage of the 3' ends of mitochondrial pre-tRNAs. Here, we report the identification of 16 novel ELAC2 variants in individuals presenting with mitochondrial respiratory chain deficiency, hypertrophic cardiomyopathy (HCM), and lactic acidosis. We provide evidence for the pathogenicity of the novel missense variants by studying the RNase Z activity in an in vitro system. We also modeled the residues affected by a missense mutation in solved RNase Z structures, providing insight into enzyme structure and function. Finally, we show that primary fibroblasts from the affected individuals have elevated levels of unprocessed mitochondrial RNA precursors. Our study thus broadly confirms the correlation of ELAC2 variants with severe infantile-onset forms of HCM and mitochondrial respiratory chain dysfunction. One rare missense variant associated with the occurrence of prostate cancer (p.Arg781His) impairs the mitochondrial RNase Z activity of ELAC2, suggesting a functional link between tumorigenesis and mitochondrial RNA metabolism.

Preliminary experience on safety of regorafenib after sorafenib failure in recurrent hepatocellular carcinoma after liver transplantation.

Regorafenib is one option for second-line treatment of hepatocellular carcinoma (HCC), improving overall survival (OS) of sorafenib-tolerant patients who develop progression. We aim to evaluate the safety and outcomes of regorafenib as second-line treatment for HCC recurrence after liver transplantation (LT). This is a retrospective, multicenter, international study including regorafenib-treated LT patients (2015-2018), with analysis of baseline characteristics and evolutionary events during sorafenib/regorafenib treatment. Twenty-eight LT patients (57 years, 7% cirrhotics, 54% performance status 1) were included. Median time from LT to regorafenib initiation was 3.9 (1.1-18.5) years; median time on sorafenib was 11.3 (0.7-76.4) months and 14 (1-591) days from sorafenib discontinuation to regorafenib. During regorafenib (6.3 months), all patients had at least one adverse event (AE), the most common grade 3/4 AEs were fatigue (n = 7) and dermatological reaction (n = 5). While no liver rejection was observed, plasma levels of immunosuppressive drugs increased in five. Twenty-four patients developed progression (38% extrahepatic growth, 33% new extrahepatic lesions/vascular invasion). Median OS from regorafenib initiation was 12.9 (95% CI, 6.7-19.1) and 38.4 months (95% CI, 18.5-58.4) for the sorafenib initiation. This is the first study showing safety of regorafenib after LT, thus providing the rational of considering regorafenib in the clinical decision-making in sorafenib-tolerant patients with HCC recurrence after LT.

Frequency and phenotypic spectrum of KMT2B dystonia in childhood: A single-center cohort study.

BACKGROUND: Childhood-onset dystonia is often genetically determined. Recently, KMT2B variants have been recognized as an important cause of childhood-onset dystonia. OBJECTIVE: To define the frequency of KMT2B mutations in a cohort of dystonic patients aged <18 years at onset, the associated clinical and radiological phenotype, and the natural history of disease. METHODS: Whole-exome sequencing or customized gene panels were used to screen a cohort of 65 patients who had previously tested negative for all other known dystonia-associated genes. RESULTS: We identified 14 patients (21.5%) carrying KMT2B variants, of which 1 was classified as a variant of unknown significance. We also identified 2 additional patients carrying pathogenic mutations in GNAO1 and ATM. Overall, we established a definitive genetic diagnosis in 23% of cases. We observed a spectrum of clinical manifestations in KMT2B variant carriers, ranging from generalized dystonia to short stature or intellectual disability alone, even within the same family. In 78.5% of cases, dystonia involved the lower limbs at onset, with later caudocranial generalization. Eight patients underwent pallidal DBS with a median decrease of Burke-Fahn-Marsden Dystonia Rating Scale-Motor score of 38.5% in the long term. We also report on 4 asymptomatic carriers, suggesting that some KMT2B mutations may be associated with incomplete disease penetrance. CONCLUSIONS: KMT2B mutations are frequent in childhood-onset dystonia and cause a complex neurodevelopmental syndrome, often featuring growth retardation and intellectual disability as additional phenotypic features. A dramatic and long-lasting response to DBS is characteristic of DYT-KMT2B dystonia. © 2019 International Parkinson and Movement Disorder Society.

COQ4 mutations cause a broad spectrum of mitochondrial disorders associated with CoQ10 deficiency.

Primary coenzyme Q10 (CoQ10) deficiencies are rare, clinically heterogeneous disorders caused by mutations in several genes encoding proteins involved in CoQ10 biosynthesis. CoQ10 is an essential component of the electron transport chain (ETC), where it shuttles electrons from complex I or II to complex III. By whole-exome sequencing, we identified five individuals carrying biallelic mutations in COQ4. The precise function of human COQ4 is not known, but it seems to play a structural role in stabilizing a multiheteromeric complex that contains most of the CoQ10 biosynthetic enzymes. The clinical phenotypes of the five subjects varied widely, but four had a prenatal or perinatal onset with early fatal outcome. Two unrelated individuals presented with severe hypotonia, bradycardia, respiratory insufficiency, and heart failure; two sisters showed antenatal cerebellar hypoplasia, neonatal respiratory-distress syndrome, and epileptic encephalopathy. The fifth subject had an early-onset but slowly progressive clinical course dominated by neurological deterioration with hardly any involvement of other organs. All available specimens from affected subjects showed reduced amounts of CoQ10 and often displayed a decrease in CoQ10-dependent ETC complex activities. The pathogenic role of all identified mutations was experimentally validated in a recombinant yeast model; oxidative growth, strongly impaired in strains lacking COQ4, was corrected by expression of human wild-type COQ4 cDNA but failed to be corrected by expression of COQ4 cDNAs with any of the mutations identified in affected subjects. COQ4 mutations are responsible for early-onset mitochondrial diseases with heterogeneous clinical presentations and associated with CoQ10 deficiency.

New genes and pathomechanisms in mitochondrial disorders unraveled by NGS technologies.

Next Generation Sequencing (NGS) technologies are revolutionizing the diagnostic screening for rare disease entities, including primary mitochondrial disorders, particularly those caused by nuclear gene defects. NGS approaches are able to identify the causative gene defects in small families and even single individuals, unsuitable for investigation by traditional linkage analysis. These technologies are contributing to fill the gap between mitochondrial disease cases defined on the basis of clinical, neuroimaging and biochemical readouts, which still outnumber by approximately 50% the cases for which a molecular-genetic diagnosis is attained. We have been using a combined, two-step strategy, based on targeted genes panel as a first NGS screening, followed by whole exome sequencing (WES) in still unsolved cases, to analyze a large cohort of subjects, that failed to show mutations in mtDNA and in ad hoc sets of specific nuclear genes, sequenced by the Sanger's method. Not only this approach has allowed us to reach molecular diagnosis in a significant fraction (20%) of these difficult cases, but it has also revealed unexpected and conceptually new findings. These include the possibility of marked variable penetrance of recessive mutations, the identification of large-scale DNA rearrangements, which explain spuriously heterozygous cases, and the association of mutations in known genes with unusual, previously unreported clinical phenotypes. Importantly, WES on selected cases has unraveled the presence of pathogenic mutations in genes encoding non-mitochondrial proteins (e.g. the transcription factor E4F1), an observation that further expands the intricate genetics of mitochondrial disease and suggests a new area of investigation in mitochondrial medicine. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

Exome sequence reveals mutations in CoA synthase as a cause of neurodegeneration with brain iron accumulation.

Neurodegeneration with brain iron accumulation (NBIA) comprises a clinically and genetically heterogeneous group of disorders with progressive extrapyramidal signs and neurological deterioration, characterized by iron accumulation in the basal ganglia. Exome sequencing revealed the presence of recessive missense mutations in COASY, encoding coenzyme A (CoA) synthase in one NBIA-affected subject. A second unrelated individual carrying mutations in COASY was identified by Sanger sequence analysis. CoA synthase is a bifunctional enzyme catalyzing the final steps of CoA biosynthesis by coupling phosphopantetheine with ATP to form dephospho-CoA and its subsequent phosphorylation to generate CoA. We demonstrate alterations in RNA and protein expression levels of CoA synthase, as well as CoA amount, in fibroblasts derived from the two clinical cases and in yeast. This is the second inborn error of coenzyme A biosynthesis to be implicated in NBIA.

Mutations in GTPBP3 cause a mitochondrial translation defect associated with hypertrophic cardiomyopathy, lactic acidosis, and encephalopathy.

Respiratory chain deficiencies exhibit a wide variety of clinical phenotypes resulting from defective mitochondrial energy production through oxidative phosphorylation. These defects can be caused by either mutations in the mtDNA or mutations in nuclear genes coding for mitochondrial proteins. The underlying pathomechanisms can affect numerous pathways involved in mitochondrial physiology. By whole-exome and candidate gene sequencing, we identified 11 individuals from 9 families carrying compound heterozygous or homozygous mutations in GTPBP3, encoding the mitochondrial GTP-binding protein 3. Affected individuals from eight out of nine families presented with combined respiratory chain complex deficiencies in skeletal muscle. Mutations in GTPBP3 are associated with a severe mitochondrial translation defect, consistent with the predicted function of the protein in catalyzing the formation of 5-taurinomethyluridine (τm(5)U) in the anticodon wobble position of five mitochondrial tRNAs. All case subjects presented with lactic acidosis and nine developed hypertrophic cardiomyopathy. In contrast to individuals with mutations in MTO1, the protein product of which is predicted to participate in the generation of the same modification, most individuals with GTPBP3 mutations developed neurological symptoms and MRI involvement of thalamus, putamen, and brainstem resembling Leigh syndrome. Our study of a mitochondrial translation disorder points toward the importance of posttranscriptional modification of mitochondrial tRNAs for proper mitochondrial function.