Mitochondrial Respiratory Chain Disorders Research Articles

Clinical, biochemical, and histopathological diagnosis of Egyptian paediatric patients with suspected mitochondrial diseases: A hospital‑based study

Background. Mitochondrial respiratory chain (RC) disorders are a growing group of disorders with a large variety of clinical presentations ranging from well-defined clinical syndromes to nonspecific manifestations, such as failure to thrive, exercise intolerance and seizures.Objective. To describe the clinical, biochemical, and histochemical spectrum of 38 Egyptian patients clinically suspected of havingmitochondrial RC disorders.Methods. A total of 38 patients (female, n=18 (47.4%); male, n=20 (52.6%)) clinically suspected of having mitochondrial diseases had been referred to the Inherited Metabolic Diseases Laboratory at Cairo University Children’s Hospital. Laboratory investigations and analyses included histochemical staining of cytochrome c oxidase and succinate dehydrogenase in muscle biopsies, as well as spectrophotometric assays of RC complexes in muscle homogenates.Results. Twenty-three patients (60.5%) were diagnosed with different RC enzyme deficiencies. Fifteen patients (65%) had complex Ideficiency and all of them also had lactic acidosis (mean (standard deviation)) plasma lactate concentration of 4 (1.65) mmol/L). Twopatients (9%) with marked complex IV deficiency both showed COX-negative ragged red fibers (RRFs) on histochemical staining.Combined complex I and complex II deficiency with scattered COX-stain deficiency and RRFs was diagnosed in 2 patients (5.25%), whilea further 2 patients (5.26%) had combined (complex I, II+III, complex IV) deficiencies. Isolated complex II deficiency was diagnosed in2 patients (5.26%) and 15 (39.5%) patients had normal RC enzyme activities.Conclusion. Biochemical assay of RC complexes is considered the cornerstone for diagnosis of RC complex mitochondrial disorders.These disorders are common among Egyptian paediatric patients.

Potential Biomarkers of Mitochondrial Dysfunction Associated with COVID-19 Infection.

Mitochondria play crucial roles in modulating immune responses, and viruses can in turn moderate mitochondrial functioning. Therefore, it is not judicious to assume that clinical outcome experienced in patients with COVID-19 or long COVID may be influenced by mitochondrial dysfunction in this infection. Also, patients who are predisposed to mitochondrial respiratory chain (MRC) disorders may be more susceptible to worsened clinical outcome associated with COVID-19 infection and long COVID. MRC disorders and dysfunction require a multidisciplinary approach for their diagnosis of which blood and urinary metabolite analysis may be utilized, including the measurement of lactate, organic acid and amino acid levels. More recently, hormone-like cytokines including fibroblast growth factor-21 (FGF-21) have also been used to assess possible evidence of MRC dysfunction. In view of their association with MRC dysfunction, assessing evidence of oxidative stress parameters including GSH and coenzyme Q10 (CoQ10) status may also provide useful biomarkers for diagnosis of MRC dysfunction. To date, the most reliable biomarker available for assessing MRC dysfunction is the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ. Moreover, the combined use of these biomarkers in a multiplexed targeted metabolic profiling strategy may further improve the diagnostic yield of the individual tests for assessing evidence of mitochondrial dysfunction in patients pre- and post-COVID-19 infection.

MITOCHONDRIAL RESPIRATORY CHAIN DISORDERS WITH VESICOURETERAL REFLUX: A PEDIATRIC CASE REPORT

Mitochondrial respiratory chain disorders (MRCD) constitute a highly heterogeneous group both with regard to clinical manifestations and underlying genetic/biochemical defects. Management of urological complications such as vesicoureteral reflux (VUR) has not been discussed in cases with MRCD. We report a pediatric case of MRCD with recurrent urinary tract infections (UTI) due to primary and secondary VUR.A 6-month-old boy with multiple malformations and a history of aspiration pneumonia was referred to our department for febrile UTI (fUTI). Voiding cystourethrography showed high-grade left VUR and a normal bladder. As a spontaneous resolution of VUR was not observed, he underwent left ureteral reimplantation concomitant with left orchidopexy at the age of 1 year and 7 months. Although he had fUTI immediately after surgery, no recurrence of the UTI occurred after discharge. At the age of 3 years, he had septic shock and cardiac arrest caused by aspiration pneumonia, as well as, encephalopathy following cardiopulmonary resuscitation. At this event, the diagnosis of MRCD was achieved by liver biopsy. Since the age of 4 years, he has had repeated fUTI. VCUG confirmed the bladder deformity and right VUR. He underwent vesico-cutaneostomy at the age of 6 years. The postoperative course was uneventful. No recurrence of UTI was observed at the one-year follow-up.

The Biochemical Assessment of Mitochondrial Respiratory Chain Disorders.

Mitochondrial respiratory chain (MRC) disorders are a complex group of diseases whose diagnosis requires a multidisciplinary approach in which the biochemical investigations play an important role. Initial investigations include metabolite analysis in both blood and urine and the measurement of lactate, pyruvate and amino acid levels, as well as urine organic acids. Recently, hormone-like cytokines, such as fibroblast growth factor-21 (FGF-21), have also been used as a means of assessing evidence of MRC dysfunction, although work is still required to confirm their diagnostic utility and reliability. The assessment of evidence of oxidative stress may also be an important parameter to consider in the diagnosis of MRC function in view of its association with mitochondrial dysfunction. At present, due to the lack of reliable biomarkers available for assessing evidence of MRC dysfunction, the spectrophotometric determination of MRC enzyme activities in skeletal muscle or tissue from the disease-presenting organ is considered the ‘Gold Standard’ biochemical method to provide evidence of MRC dysfunction. The purpose of this review is to outline a number of biochemical methods that may provide diagnostic evidence of MRC dysfunction in patients.

EP015: COQ5 compound heterozygous variants in a family with global developmental delay, seizures, spastic paraparesis, and stroke

Primary Coenzyme Q10 (CoQ10) Deficiency is a heterogeneous group of mitochondrial respiratory chain disorders caused by pathogenic variants in any of the genes involved in the metabolism of CoQ10. To date, only one family with CoQ10 deficiency due to COQ5 pathogenic variants has been reported. In 2018, 3 sisters were described with cerebellar ataxia, cerebellar atrophy, and other variable features, such as intellectual disability and seizures. They all had reduced CoQ10 levels in leukocytes, and reduced levels in the only muscle tissue available.

Macroscopic Characteristics of the Native Liver in Children With MPV17-Related Mitochondrial DNA Depletion Syndrome: An Indication for Performing Liver Transplantation?

Mitochondrial respiratory chain disorders (MRCDs) are rare conditions with various clinical manifestations that depend on the genetic type, with subsequent severity of the liver disease. Clinical presentations include acute liver failure or chronic liver failure with liver cirrhosis, which are cruelly progressive and fatal. We report six cases of LT for acute liver failure diagnosed pathogenic MPV17 variants. Three out of six cases were siblings with the MPV17-mutation (c.148C>T, p.R50W / c.149G>A; p.R50Q), also known as the childhood form of Navajo neurohepatopathy. Those three patients underwent LT for liver cirrhosis at the ages of 5, 7, and 7 years, respectively. All three recipients are currently doing well without any neurological sequelae. In contrast, the three additional patients that presented with an acute liver failure and subsequent diagnosis of mutation in MPV17 (homozygous c.451dupC: p.L151PfsX39; homozygous c.451dupC : p.L151PfsX39; c.451dupC : p.L151PfsX39 / c.71-2_79del11ins4), underwent LT at the ages of 4 months, 11 months, and 1 year, respectively. All three recipients died from pulmonary hypertension following successful LT. Interestingly, the intraoperative macroscopic findings of the native liver at the time of LT revealed distinctive, microgranular nodules and liver fibrosis with severe steatosis ("avocado-like" liver). LT might be contraindicated in MPV17 patients with c.451dupC mutation due to the extremely poor prognosis caused by fatal progressive pulmonary hypertension. The identification of the typical macroscopic finding ("avocado-like"), seen in such pediatric transplant candidates with acute liver failure, might be helpful to provide an early diagnosis of MPV17-related c.451dupC mutation.

Outcomes of liver transplantation for mitochondrial respiratory chain disorder in children.

Mitochondrial respiratory chain disorder (MRCD) can cause acute liver failure (ALF), which may necessitate liver transplantation (LT). However, MRCD is often difficult to diagnose before LT and the indications of LT are controversial due to the likelihood of progressive neurological disease. The present study further characterized the patient population and described the outcomes. Thirteen patients who underwent LT for MRCD from November 2005 to May 2020 were enrolled in this study. Six of 13MRCD patients were diagnosed with a mitochondrial inner membrane protein 17-related mitochondrial DNA depletion syndrome (MTDPS). Overall, nine survived with a median follow-up of 1.8years (IQR, 1.3-5.1years); four died within 2years. In the long-term, seven survivors showed no progression of hypotonia after LT and attended a normal kindergarten or primary school. Neurological abnormalities were observed in two survivors, including vison loss related to Leber's hereditary optic neuropathy in one patient and psychomotor retardation related to Leigh syndrome in the other. Three non-survivors after LT were diagnosed with MTDPS and died of severe pulmonary hypertension, which had developed at 8, 9, and 18months after LT (n=1 each). The remaining patient died of postoperative respiratory infection with respiratory syncytial virus. The long-term results support the performance of LT in patients with MRCD, although a genetic diagnosis is preferable for determining the accurate indications for LT in these patients. Furthermore, care should be taken to avoid complications due to mitochondrial dysfunction during the long-term follow-up.

The long and winding road: perspectives of people and parents of children with mitochondrial conditions negotiating management after diagnosis

BackgroundThe diagnostic odyssey for people with a rare disease is well known, but difficulties do not stop at diagnosis. Here we investigate the experience of people, or parents of children with a diagnosed mitochondrial respiratory chain disorder (MRCD) in the management of their disease. The work complements ongoing projects around implementation of consensus recommendations for management of people with MRCD. People with or caring for a child with a formally diagnosed MRCD were invited to take part in an hour-long focus group held via videoconference. Questions elicited experiences of receiving management advice or information specific to their MRCD in four areas drawn from the consensus recommendations: diet and supplements, exercise, access to social services, and mental health. Sessions were audio-recorded, transcribed and analysed using a combination of inductive and deductive coding.ResultsFocus groups were conducted with 20 participants from five Australian states in June–September 2020. Fourteen adults with a MRCD (three of whom also had a child with a MRCD), and six who cared for a child with a MRCD took part. The overarching finding was that of the need for ongoing negotiation to access the advice and service required to manage their condition. The nature of these negotiations varied across contexts but mostly related to joint decision-making, and more commonly, the need to advocate for their care with non-specialist services (e.g., dieticians, schools). The effort required for this self-advocacy was a prominent theme. While most participants reported receiving adequate advice around supplements, and to a lesser extent diet and exercise, the majority reported no formal advice around mental health or practical assistance accessing social services.ConclusionThese focus groups have revealed several gaps in the system for people with a MRCD, interacting with care providers after diagnosis. Focus group participants had to negotiate with a range of different stakeholders in order to secure appropriate advice or services. Notable was the gap in appropriate generalist services (e.g., dieticians) with sufficient knowledge of MRCD to support people with their day-to-day challenges.

Defective complex III mitochondrial respiratory chain due to a novel variant in CYC1 gene masquerades acute demyelinating syndrome or Leber hereditary optic neuropathy

Complex III (CIII) is the third out of five mitochondrial respiratory chain complexes residing at the mitochondrial inner membrane. The assembly of 10 subunits encoded by nuclear DNA and one by mitochondrial DNA result in the functional CIII which transfers electrons from ubiquinol to cytochrome c. Deficiencies of CIII are among the least investigated mitochondrial disorders and thus clinical spectrum of patients with mutations in CIII is not well defined. We report on a 10-year-old girl born to consanguineous Iranian parents presenting with recurrent visual loss episodes and optic nerve contrast enhancement in brain imaging reminiscent of an acquired demyelination syndrome (i.e. optic neuritis or multiple sclerosis), who was ultimately confirmed to have a novel homozygous missense variant of unknown significance, c.949C > T; p.(Arg317Trp) in the CYC1 gene, a nuclear DNA subunit of complex III of the mitochondrial chain. Sanger sequencing confirmed the segregation of this variant with disease in the family. The effect of this variant on the protein structure was shown in-silico. Our findings, not only expand the clinical spectrum due to defects in CYC1 gene but also highlight that mitochondrial respiratory chain disorders could be considered as a potential differential diagnosis in children who present with unusual patterns of acquired demyelination syndromes (ADS). In addition, our results support the hypothesis that mitochondrial disorders might have an overlapping presentation with ADS.

Spontaneous recovery in infantile mitochondrial hepatopathy due to TRMU gene mutation

Background: Depending on the genetic mutation, mitochondrial hepatopathy has a variable presentation. Spontaneous recovery is a rare occurrence in these patients. However, complete recovery is possible in infants having t-RNA5-methylaminomethyl-2-thiouridylate methyl-transferase (TRMU) gene mutation. Case presentation: A 53-day-old female child presented with hepatopathy and lactic acidosis. Genetic work up showed she has a mitochondrial respiratory chain disorder due to the TRMU gene mutation. Very few patients with isolated hepatic involvement have been described in the literature. We are reporting the first case from India of transient hepatopathy due to heterozygous TRMU gene mutation. Recovery was spontaneous at 4 months of age. Conclusion: Complete recovery is possible in infants having TRMU mutation if they are supported through and survive the acute phase. The identification of TRMU mutation could impact clinical management.

Advanced pathologic study for definite diagnosis of mitochondrial cardiomyopathy

Abstract Mitochondrial cardiomyopathy (MCM) is usually recognized as one of the phenotypes of systemic mitochondrial disease. However if there are no cardiac symptoms, it is difficult to make a definite diagnosis because of various cardiovascular phenotypes and no diagnostic criteria in pathological examination. To add myocardial pathology to the diagnostic criteria for mitochondrial respiratory chain disorders, which is the gold standard in the diagnosis of mitochondrial diseases, we performed quantitative analysis of mitochondria using electron microscopy and immunohistopathologic analysis with respiratory chain enzyme antibodies. Ten patients with hypertrophic or restrictive cardiomyopathy who had undergone endomyocardial biopsy were studied. Respiratory chain enzymatic assay and genetic study were performed and four patients were diagnosed with MCM. Using electron microscopy with quantitative analysis, volume density of mitochondria within cardiac muscle cells was significantly increased in the MCM group compared to the non-MCM group (p=0.013). Immunohistopathologic results were compatible with the result of the respiratory chain enzymatic assay. These advanced pathological tests can distinguish MCM from other cardiomyopathies. Results of immunopathologic study Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, AMED.

CoQ10 Deficient Endothelial Cell Culture Model for the Investigation of CoQ10 Blood-Brain Barrier Transport.

Primary coenzyme Q10 (CoQ10) deficiency is unique among mitochondrial respiratory chain disorders in that it is potentially treatable if high-dose CoQ10 supplements are given in the early stages of the disease. While supplements improve peripheral abnormalities, neurological symptoms are only partially or temporarily ameliorated. The reasons for this refractory response to CoQ10 supplementation are unclear, however, a contributory factor may be the poor transfer of CoQ10 across the blood–brain barrier (BBB). The aim of this study was to investigate mechanisms of CoQ10 transport across the BBB, using normal and pathophysiological (CoQ10 deficient) cell culture models. The study identifies lipoprotein-associated CoQ10 transcytosis in both directions across the in vitro BBB. Uptake via SR-B1 (Scavenger Receptor) and RAGE (Receptor for Advanced Glycation Endproducts), is matched by efflux via LDLR (Low Density Lipoprotein Receptor) transporters, resulting in no “net” transport across the BBB. In the CoQ10 deficient model, BBB tight junctions were disrupted and CoQ10 “net” transport to the brain side increased. The addition of anti-oxidants did not improve CoQ10 uptake to the brain side. This study is the first to generate in vitro BBB endothelial cell models of CoQ10 deficiency, and the first to identify lipoprotein-associated uptake and efflux mechanisms regulating CoQ10 distribution across the BBB. The results imply that the uptake of exogenous CoQ10 into the brain might be improved by the administration of LDLR inhibitors, or by interventions to stimulate luminal activity of SR-B1 transporters.

Advanced pathological study for definite diagnosis of mitochondrial cardiomyopathy.

Mitochondrial cardiomyopathy (MCM) is difficult to make a definite diagnosis because of various cardiovascular phenotypes and no diagnostic criteria in the pathology examination. We aim to add myocardial pathology to the diagnostic criteria for mitochondrial respiratory chain disorders. Quantitative analysis of mitochondria using electron microscopy and immunohistopathological analysis with respiratory chain enzyme antibodies were performed in 11 patients with hypertrophic or restrictive cardiomyopathy who underwent endomyocardial biopsy for possible MCM . Respiratory chain enzymatic assay in biopsied myocardium and genetic studies were also performed in all the subjects to define MCM. Four patients were diagnosed with MCM according to the recent criteria of mitochondrial respiratory chain disorders. Using electron microscopy with quantitative analysis, the volume density of mitochondria within cardiac muscle cells was significantly increased in the MCM group compared with the non-MCM group (p=0.007). Immunohistopathological results were compatible with the result of the respiratory chain enzymatic assay. Pathological diagnosis of MCM could be confirmed by a quantitative study of electron microscopy and immunohistopathological analysis using the mitochondrial respiratory chain enzyme subunit antibody.

DNA Methylation Associated with Mitochondrial Dysfunction in a South African Autism Spectrum Disorder Cohort.

Autism spectrum disorder (ASD) is characterized by phenotypic heterogeneity and a complex genetic architecture which includes distinctive epigenetic patterns. We report differential DNA methylation patterns associated with ASD in South African children. An exploratory whole‐epigenome methylation screen using the Illumina 450 K MethylationArray identified differentially methylated CpG sites between ASD and controls that mapped to 898 genes (P ≤ 0.05) which were enriched for nine canonical pathways converging on mitochondrial metabolism and protein ubiquitination. Targeted Next Generation Bisulfite Sequencing of 27 genes confirmed differential methylation between ASD and control in our cohort. DNA pyrosequencing of two of these genes, the mitochondrial enzyme Propionyl‐CoA Carboxylase subunit Beta (PCCB) and Protocadherin Alpha 12 (PCDHA12), revealed a wide range of methylation levels (9–49% and 0–54%, respectively) in both ASD and controls. Three CpG loci were differentially methylated in PCCB (P ≤ 0.05), while PCDHA12, previously linked to ASD, had two significantly different CpG sites (P ≤ 0.001) between ASD and control. Differentially methylated CpGs were hypomethylated in ASD. Metabolomic analysis of urinary organic acids revealed that three metabolites, 3‐hydroxy‐3‐methylglutaric acid (P = 0.008), 3‐methyglutaconic acid (P = 0.018), and ethylmalonic acid (P = 0.043) were significantly elevated in individuals with ASD. These metabolites are directly linked to mitochondrial respiratory chain disorders, with a putative link to PCCB, consistent with impaired mitochondrial function. Our data support an association between DNA methylation and mitochondrial dysfunction in the etiology of ASD. Autism Res 2020, 13: 1079‐1093. © 2020 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc.Lay SummaryEpigenetic changes are chemical modifications of DNA which can change gene function. DNA methylation, a type of epigenetic modification, is linked to autism. We examined DNA methylation in South African children with autism and identified mitochondrial genes associated with autism. Mitochondria are power‐suppliers in cells and mitochondrial genes are essential to metabolism and energy production, which are important for brain cells during development. Our findings suggest that some individuals with ASD also have mitochondrial dysfunction.

Broadening the phenotypic spectrum of Pearson syndrome: Five new cases and a review of the literature.

Pearson syndrome (PS) is a multisystem mitochondrial respiratory chain disorder typically characterized by sideroblastic anemia and exocrine pancreatic insufficiency. PS is caused by a single large-scale mitochondrial DNA (mtDNA) deletion. PS classically presents in the first year of life and may be fatal in infancy. Children who survive PS may progress to develop Kearns-Sayre syndrome later in life. The full phenotypic spectrum and prognosis of the condition continue to evolve. Here we report five new patients with PS with unique clinical presentations, including four patients with onset later than previously reported in the literature, and one patient with prenatal onset of symptoms. The timing and unique features of these presentations support an expanded phenotypic spectrum of single large-scale mtDNA deletion syndromes (SLSMDS) and reinforce the importance of including SLSMDS in the differential for children with complex multisystem presentations.

Primary Coenzyme Q deficiency Due to Novel ADCK3 Variants, Studies in Fibroblasts and Review of Literature.

Primary deficiency of coenzyme Q10 (CoQ10 ubiquinone), is classified as a mitochondrial respiratory chain disorder with phenotypic variability. The clinical manifestation may involve one or multiple tissue with variable severity and presentation may range from infancy to late onset. ADCK3 gene mutations are responsible for the most frequent form of hereditary CoQ10 deficiency (Q10 deficiency-4 OMIM #612016) which is mainly associated with autosomal recessive spinocerebellar ataxia (ARCA2, SCAR9). Here we provide the clinical, biochemical and genetic investigation for unrelated three nuclear families presenting an autosomal form of Spino-Cerebellar Ataxia due to novel mutations in the ADCK3 gene. Using next generation sequence technology we identified a homozygous Gln343Ter mutation in one family with severe, early onset of the disease and compound heterozygous mutations of Gln343Ter and Ser608Phe in two other families with variable manifestations. Biochemical investigation in fibroblasts showed decreased activity of the CoQ dependent mitochondrial respiratory chain enzyme succinate cytochrome c reductase (complex II + III). Exogenous CoQ slightly improved enzymatic activity, ATP production and decreased oxygen free radicals in some of the patient's cells. Our results are presented in comparison to previously reported mutations and expanding the clinical, molecular and biochemical spectrum of ADCK3 related CoQ10 deficiencies.

Clinical and neuroimaging features of the m.10197G>A mtDNA mutation: New case reports and expansion of the phenotype variability

Complex I (CI) is the largest component of the mitochondrial respiratory chain (MRC) and it is made up of 7 mitochondrial DNA (mtDNA)-encoded and at least 38 nuclear DNA-encoded subunits. Isolated CI deficiency is the most common single enzyme deficiency in the heterogeneous group of MRC disorders and it is a relatively common etiology of Leigh-like syndrome (LS).With a few exceptions, descriptions of the clinical spectrum of specific mutations in CI are scarce. We here present three unrelated Italian children who harbored the homoplasmic m.10197G>A mutation in MT-ND3 associated with reduced enzyme activity of CI in muscle. Compared with the spectrum of phenotypes seen in 13 previously described families with the same mutation, these children showed some novel clinical features. Two of the boys presented with subacute onset of dystonia, which showed a remitting-relapsing clinical course in one of them. The third boy presented acute symptoms consisting of speech impairment, progressive left-sided hemiparesis, and also vertebral and arterial malformations. In all the children, molecular studies identified a similar mutation load in tissues, and neuroimaging findings were consistent with the features seen in LS. Functional investigations in cultured skin fibroblasts suggested low ATP production in homoplasmic cells. Our results confirm that the m.10197G>A mutation is relevant to these patients' clinical and biochemical phenotypes, which thus expand the array of phenotypes associated with this variant.

Lipidomic profiling of plasma samples from patients with mitochondrial disease

Mitochondrial disease (MD) is a rare mitochondrial respiratory chain disorder with a high mortality and extremely challenging to treat. Although genomic, transcriptomic, and proteomic analyses have been performed to investigate the pathogenesis of MD, the role of metabolomics in MD, particularly of lipidomics remains unclear. This study was undertaken to identify potential lipid biomarkers of MD. An untargeted lipidomic approach was used to compare the plasma lipid metabolites in 20 MD patients and 20 controls through Liquid Chromatography coupled to Mass Spectrometry. Volcano plot analysis was performed to identify the different metabolites. Receiver operating characteristic (ROC) curves were constructed and the area under the ROC curves (AUC) was calculated to determine the potentially sensitive and specific biomarkers. A total of 41 lipids were significantly different in MD patients and controls. ROC curve analysis showed the top 5 AUC values of lipids (phosphatidylinositols 38:6, lysoPC 20:0, 19:0, 18:0, 17:0) are more than 0.99. Multivariate ROC curve based exploratory analysis showed the AUC of combination of top 5 lipids is 1, indicating they may be potentially sensitive and specific biomarkers for MD. We propose combination of these lipid species may be more valuable in predicting the development and progression of MD, and this will have important implications for the diagnosis and treatment of MD.

Liver Transplantation for Mitochondrial Respiratory Chain Disorder: A Single-Center Experience and Excellent Marker of Differential Diagnosis

Mitochondrial respiratory chain disorder (MRCD) can cause liver failure requiring liver transplantation (LT), although it is often difficult to diagnose before LT. From 2005 to 2016, 9 MRCD patients with the median age at LT of 6 months underwent LT in our institute. Their clinical courses were retrospectively reviewed and the laboratory parameters were compared between the MRCD patients and 10 patients with acute liver failure unrelated to MRCD (non-MRCD). Five patients had extrahepatic manifestations, including developmental disorders in 3 and failure to thrive in 3, before LT. Only 3 patients (33.3%) were diagnosed before LT. Between MRCD and non-MRCD, lactate was significantly high and lactate-to-pyruvate ratio (L/P ratio) tended to be higher in MRCD. From the receiver operating characteristic curve, the optimal cutoff value of lactate was 50.0 mg/dL and that of L/P ratio was 23.2. Patient survival rate of MRCD was 77.8%, although 2 patients with mitochondrial depletion syndrome suffered from de novo pulmonary hypertension after LT. Our experiences showed the difficulty of preoperative diagnosis, and preoperative extrahepatic manifestations did not always mean poor outcome. Our study showed that lactate value and L/P ratio can be excellent predictors of MRCD.

Clinical validity of biochemical and molecular analysis in diagnosing Leigh syndrome: a study of 106 Japanese patients

Leigh syndrome (LS) is a progressive neurodegenerative disorder of infancy and early childhood. It is clinically diagnosed by typical manifestations and characteristic computed tomography (CT) or magnetic resonance imaging (MRI) studies. Unravelling mitochondrial respiratory chain (MRC) dysfunction behind LS is essential for deeper understanding of the disease, which may lead to the development of new therapies and cure. The aim of this study was to evaluate the clinical validity of various diagnostic tools in confirming MRC disorder in LS and Leigh-like syndrome (LL). The results of enzyme assays, molecular analysis, and cellular oxygen consumption rate (OCR) measurements were examined. Of 106 patients, 41 were biochemically and genetically verified, and 34 had reduced MRC activity but no causative mutations. Seven patients with normal MRC complex activities had mutations in the MT-ATP6 gene. Five further patients with normal activity in MRC were identified with causative mutations. Conversely, 12 out of 60 enzyme assays performed for genetically verified patients returned normal results. No biochemical or genetic background was confirmed for 19 patients. OCR was reduced in ten out of 19 patients with negative enzyme assay results. Inconsistent enzyme assay results between fibroblast and skeletal muscle biopsy samples were observed in 33% of 37 simultaneously analyzed cases. These data suggest that highest diagnostic rate is reached using a combined enzymatic and genetic approach, analyzing more than one type of biological materials where suitable. Microscale oxygraphy detected MRC impairment in 50% cases with no defect in MRC complex activities.