Single Large-scale Mitochondrial DNA Deletions Research Articles

Long-term hematopoietic dysfunction in patients with large-scale mitochondrial DNA deletion syndromes.

Pearson syndrome (PS) and Kearns-Sayre syndrome (KSS) are single large-scale mitochondrial DNA deletion (SLSMD) syndromes. PS is characterized by severe, transient childhood cytopenia, whereas KSS typically manifests later in life without hematologic abnormalities. Despite distinct clinical presentations, both share a common mitochondrial DNA deletion. Recent observations suggest a potential link between PS progression and myeloid malignancy development, indicating that bone marrow failure (BMF) may be a key aspect of PS pathology and potentially universal across SLSMDs. This study explores longitudinal hematological manifestations of SLSMD syndromes, focusing on bone marrow (BM) dysfunction. Sixteen patients with SLSMDs (13 PS and 3 KSS) were followed, of whom 75% experienced cytopenia, necessitating blood transfusions in 56%. Despite achieving transfusion independence at a median age of 24 months, persistent hematological abnormalities were noted. Comprehensive longitudinal BM studies were conducted in 62% of subjects and consistently revealed signs of marrow dysfunction, even without concurrent cytopenia. Median BM cellularity at a median age of four years and eight months was 50%, with histological signs of dyserythropoiesis, abnormal megakaryocytes, and signs suggesting myelodysplasia. Reduced CD34+ counts and BM colony-forming unit capacity were noted, alongside chromosome 7 aberrations in 16% of patients on cytogenetic studies. Our findings establish BM dysfunction as a persistent hallmark of SLSMD syndromes, posing a risk of clonal evolution and acquisition of chromosome 7 aberrations. This aligns with recent literature, emphasizing enduring BMF in SLSMD syndromes and advocating for tailored hematological monitoring guidelines for this unique patient cohort.

Long-Term Hematopoietic Dysfunction in Patients with Single Large-Scale Mitochondrial DNA Deletion Syndromes

Pearson syndrome (PS) is the only single large-scale mitochondrial DNA deletion syndrome (SLSMDs) presenting substantial hematologic manifestations, usually a severe though transient cytopenia of childhood. Recently, progression to myeloid malignancies has been described among PS patients. Older PS patients, as well as patients with SLSMDs presenting with Kearns-Sayre syndrome (KSS) or with progressive external ophthalmoplegia (PEO), do not display hematologic abnormalities. Since the underlying mitochondrial DNA deletion is similar in all SLSMDs, we hypothesized that bone marrow (BM) dysfunction is a common and persistent manifestation in these patients. We studied 16 patients with molecular-confirmed SLSMDs: 13 with PS, and three with KSS. The median age at diagnosis was 25 months (range 2-136 months). Seventy-five percent of patients presented with cytopenia in infancy, and 56% required blood products. Resolution of cytopenia occurred in 92% of this subgroup, at a median age of 24 months (range 12-39 months). BM studies were performed in all patients, and 56% of patients had multiple BM evaluations. All BM biopsies examined showed signs of marrow dysfunction, including in patients without a history of cytopenia. Median BM cellularity was 50% (range 30-80%) at a median age of 5 years. BM samples showed a paucity of precursor myeloid cells, signs of dyserythropoiesis, and abnormal or missing megakaryocytes. We report low hematopoietic stem and progenitor cell functionality in patients with SLSMDs: The median CD34+ count was 0.68% (range 0.27-1.92%, expected range 1-2%). BM colony forming unit (CFU) capacity was reduced in SLSMD patients: the median CFU in patients was 280 per 10 6 cells compared to 1090 per 10 6 cells in healthy controls (p=0.004). Conventional cytogenetic analysis was done on 10 patients (62%), and FISH analysis was done on 15 patients (93%). Monosomy 7 was identified in seven patients (44%): in one patient the monosomy 7 resolved in a follow-up BM assay. Another patient with signs of myelodysplasia and 30% of the BM cells having monosomy 7 was referred to an allogeneic bone marrow transplantation. To conclude, long-term BM dysfunction is evident in all patients with SLSMD and includes a risk of developing clonal evolution and monosomy 7. This data, combined with other recent publications, highlights the ongoing marrow failure and suggest that SLSMD syndromes should be included under inherited BM failure syndromes.

Adrenocortical function in patients with Single Large Scale Mitochondrial DNA Deletions: a retrospective single centre cohort study.

Single Large Scale Mitochondrial DNA Deletions (SLSMDs), Pearson Syndrome (PS) and Kearns-Sayre Syndrome (KSS), are systemic diseases with multiple endocrine abnormalities. The adrenocortical function has not been systematically investigated with a few anecdotal reports of overt adrenal insufficiency (AI). The study aimed to assess the adrenocortical function in a large cohort of SLSMDs. A retrospective monocentric longitudinal study involved a cohort of 18 SLSMDs patients. Adrenocortical function was evaluated by baseline adrenocorticotrophic hormone (ACTH) and cortisol measurements and by high- (HDT) and low-dose (LDT) ACTH stimulation tests and compared with 92 healthy controls (HC). Baseline adrenocortical function was impaired in 39% of patients and by the end of the study, 66% of PS and 25% of KSS showed an insufficient increase after ACTH stimulation, with cortisol deficiency due to primary AI in most PS and subclinical AI in KSS. Symptomatic AI was recorded in 44% of patients. Peak cortisol levels after ACTH stimulation tests were significantly lower in patients than in HC (P < .0001), with a more reduced response to LDT vs HDT (P < .05). Our study highlights that cortisol deficiency due to primary AI represents a relevant part of the clinical spectrum in SLSMDs, with more severe impairment in PS than in KSS. Basal and after-stimulus assessment of adrenocortical axis should be early and regularly investigated to identify any degree of adrenocortical dysfunction. The study allowed the elaboration of a diagnostic process designed for the diagnosis, treatment, and follow-up of adrenocortical abnormalities in SLSMDs.

Mitochondrial augmentation of hematopoietic stem cells in children with single large-scale mitochondrial DNA deletion syndromes

Patients with single large-scale mitochondrial DNA (mtDNA) deletion syndromes (SLSMDs) usually present with multisystemic disease, either as Pearson syndrome in early childhood or as Kearns-Sayre syndrome later in life. No disease-modifying therapies exist for SLSMDs. We have developed a method to enrich hematopoietic cells with exogenous mitochondria, and we treated six patients with SLSMDs through a compassionate use program. Autologous CD34+ hematopoietic cells were augmented with maternally derived healthy mitochondria, a technology termed mitochondrial augmentation therapy (MAT). All patients had substantial multisystemic disease involvement at baseline, including neurologic, endocrine, or renal impairment. We first assessed safety, finding that the procedure was well tolerated and that all study-related severe adverse events were either leukapheresis-related or related to the baseline disorder. After MAT, heteroplasmy decreased in the peripheral blood in four of the six patients. An increase in mtDNA content of peripheral blood cells was measured in all six patients 6 to 12 months after MAT as compared baseline. We noted some clinical improvement in aerobic function, measured in patients 2 and 3 by sit-to-stand or 6-min walk testing, and an increase in the body weight of five of the six patients suffering from very low body weight before treatment. Quality-of-life measurements as per caregiver assessment and physical examination showed improvement in some parameters. Together, this work lays the ground for clinical trials of MAT for the treatment of patients with mtDNA disorders.

Development and characterization of cell models harbouring mtDNA deletions for in vitro study of Pearson syndrome.

ABSTRACTPearson syndrome is a rare multisystem disease caused by single large-scale mitochondrial DNA deletions (SLSMDs). The syndrome presents early in infancy and is mainly characterised by refractory sideroblastic anaemia. Prognosis is poor and treatment is supportive, thus the development of new models for the study of Pearson syndrome and new therapy strategies is essential. In this work, we report three different cell models carrying an SLMSD: fibroblasts, transmitochondrial cybrids and induced pluripotent stem cells (iPSCs). All studied models exhibited an aberrant mitochondrial ultrastructure and defective oxidative phosphorylation system function, showing a decrease in different parameters, such as mitochondrial ATP, respiratory complex IV activity and quantity or oxygen consumption. Despite this, iPSCs harbouring ‘common deletion’ were able to differentiate into three germ layers. Additionally, cybrid clones only showed mitochondrial dysfunction when heteroplasmy level reached 70%. Some differences observed among models may depend on their metabolic profile; therefore, we consider that these three models are useful for the in vitro study of Pearson syndrome, as well as for testing new specific therapies. This article has an associated First Person interview with the first author of the paper.

Renal Phenotype in Mitochondrial Diseases: A Multicenter Study

Aims: This study aimed to investigate associations between renal and extrarenal manifestations of mitochondrial diseases and their natural history as well as predictors of renal disease severity and overall disease outcome. The secondary aim was to generate a protocol of presymptomatic assessment and monitoring of renal function in patients with a defined mitochondrial disease. Methods: A multicenter, retrospective cohort study was performed by the Mitochondrial Clinical and Research Network (MCRN). Patients of any age with renal manifestations associated with a genetically verified mitochondrial disease were included from 8 expert European centers specializing in mitochondrial diseases: Gothenburg, Oulu, Copenhagen, Bergen, Helsinki, Stockholm, Rotterdam, and Barcelona. Results: Of the 36 patients included, two-thirds had mitochondrial DNA-associated disease. Renal manifestations were the first sign of mitochondrial disease in 19%, and renal involvement was first identified by laboratory tests in 57% of patients. Acute kidney injury occurred in 19% of patients and was the first sign of renal disease in the majority of these. The most common renal manifestation was chronic kidney disease (75% with stage 2 or greater), followed by tubulopathy (44.4%), the latter seen mostly among patients with single large-scale mitochondrial DNA deletions. Acute kidney injury and tubulopathy correlated with worse survival outcome. The most common findings on renal imaging were increased echogenicity and renal dysplasia/hypoplasia. Renal histology revealed focal segmental glomerulosclerosis, nephrocalcinosis, and nephronophthisis. Conclusion: Acute kidney injury is a distinct renal phenotype in patients with mitochondrial disease. Our results highlight the importance to recognize renal disease as a sign of an underlying mitochondrial disease. Acute kidney injury and tubulopathy are 2 distinct indicators of poor survival in patients with mitochondrial diseases.

Phenotypic spectrum and clinical course of single large-scale mitochondrial DNA deletion disease in the paediatric population: a multicentre study

BackgroundLarge-scale mitochondrial DNA deletions (LMD) are a common genetic cause of mitochondrial disease and give rise to a wide range of clinical features. Lack of longitudinal data means the natural...

Pediatric single large-scale mtDNA deletion syndromes: The power of patient reported outcomes

There is a limited understanding of system-level clinical outcomes and interventions associated with single large-scale mitochondrial DNA deletion syndromes (SLSMDS). Additionally, no research exists that describes patient reported outcomes (PROs) of children with SLSMDS.A global and observational registry was established to understand the multi-systemic course of SLSMDS and track clinical outcomes. The development and design of the registry is described. Demographic characteristics, history and diagnoses, and system level prevalence of problems and interventions are reported for 42 children. System level problems and interventions include information on the following body systems: audiology, cardiac, endocrine, gastrointestinal (including pancreatic and hepatobiliary system), hematological, metabolic, neurological (including autonomic, mobility, & learning), ophthalmic, psychiatric, renal, and respiratory.Results emphasize the need of patient registries and suggest that the diagnostic odyssey and burden of disease for children with SLSMDS is significant. System-level findings may help families and clinical providers with diagnosis, prognostication, and treatment. A multidisciplinary team of clinical experts with a central coordinating specialist for children with SLSMDS is recommended.

The Phenotypic Spectrum of 47 Czech Patients with Single, Large-Scale Mitochondrial DNA Deletions.

Background: In this retrospective study, we analysed clinical, biochemical and molecular genetic data of 47 Czech patients with Single, Large-Scale Mitochondrial DNA Deletions (SLSMD). Methods: The diagnosis was based on the long-range PCR (LX-PCR) screening of mtDNA isolated from muscle biopsy in 15 patients, and from the buccal swab, urinary epithelial cells and blood in 32 patients. Results: A total of 57% patients manifested before the age of 16. We did not find any significant difference between paediatric and adult manifestation in either the proportion of patients that would develop extraocular symptoms, or the timespan of its progression. The survival rate in patients with Pearson Syndrome reached 60%. Altogether, five patients manifested with atypical phenotype not fulfilling the latest criteria for SLSMD. No correlation was found between the disease severity and all heteroplasmy levels, lengths of the deletion and respiratory chain activities in muscle. Conclusions: Paediatric manifestation of Progressive External Ophthalmoplegia (PEO) is not associated with a higher risk of multisystemic involvement. Contrary to PEO and Kearns-Sayre Syndrome Spectrum, Pearson Syndrome still contributes to a significant childhood mortality. SLSMD should be considered even in cases with atypical presentation. To successfully identify carriers of SLSMD, a repeated combined analysis of buccal swab and urinary epithelial cells is needed.

The urinary organic acids profile in single large-scale mitochondrial DNA deletion disorders

Single large-scale mitochondrial DNA deletions disorders are classified into three main phenotypes with frequent clinical overlap: Pearson marrow-pancreas syndrome (PMS), Kearns-Sayre syndrome (KSS) and chronic progressive external ophtalmoplegia (PEO). So far, only few anecdotal studies have reported on the urinary organic acids profile in this disease class.In this single-center retrospective study, we performed quantitative evaluation of urinary organic acids in a series of 15 pediatric patients, 7 with PMS and 8 with KSS.PMS patients showed an organic acids profile almost constantly altered, whereas KSS patients frequently presented with normal profiles. Lactate, 3-hydroxybutyrate, 3-hydroxyisobutyrate, fumarate, pyruvate, 2-hydroxybutyrate, 2-ethyl-3-hydroxypropionate, and 3-methylglutaconate represented the most frequent metabolites observed in PMS urine. We also found novel metabolites, 3-methylglutarate, tiglylglycine and 2-methyl-2,3-dihydroxybutyrate, so far never reported in this disease. Interestingly, patients with a disease onset as PMS evolving overtime into KSS phenotype, presented persistent and more pronounced alterations of organic acid signature than in patients with a pure KSS phenotype.Our study shows that the quantitative analysis of urinary organic acid profile represents a helpful tool for the diagnosis of PMS and for the differential diagnosis with other inherited diseases causing abnormal organic acidurias.

Pathological mechanisms underlying single large-scale mitochondrial DNA deletions.

ObjectiveSingle, large‐scale deletions in mitochondrial DNA (mtDNA) are a common cause of mitochondrial disease. This study aimed to investigate the relationship between the genetic defect and molecular phenotype to improve understanding of pathogenic mechanisms associated with single, large‐scale mtDNA deletions in skeletal muscle.MethodsWe investigated 23 muscle biopsies taken from adult patients (6 males/17 females with a mean age of 43 years) with characterized single, large‐scale mtDNA deletions. Mitochondrial respiratory chain deficiency in skeletal muscle biopsies was quantified by immunoreactivity levels for complex I and complex IV proteins. Single muscle fibers with varying degrees of deficiency were selected from 6 patient biopsies for determination of mtDNA deletion level and copy number by quantitative polymerase chain reaction.ResultsWe have defined 3 “classes” of single, large‐scale deletion with distinct patterns of mitochondrial deficiency, determined by the size and location of the deletion. Single fiber analyses showed that fibers with greater respiratory chain deficiency harbored higher levels of mtDNA deletion with an increase in total mtDNA copy number. For the first time, we have demonstrated that threshold levels for complex I and complex IV deficiency differ based on deletion class.InterpretationCombining genetic and immunofluorescent assays, we conclude that thresholds for complex I and complex IV deficiency are modulated by the deletion of complex‐specific protein‐encoding genes. Furthermore, removal of mt‐tRNA genes impacts specific complexes only at high deletion levels, when complex‐specific protein‐encoding genes remain. These novel findings provide valuable insight into the pathogenic mechanisms associated with these mutations. Ann Neurol 2018;83:115–130

Detection of single large-scale mitochondrial DNA deletions by MLPA technique

Detection of single large-scale mitochondrial DNA deletions by MLPA technique

Genotype and phenotype analyses in 136 patients with single large-scale mitochondrial DNA deletions

We examined 136 patients with mitochondrial DNA (mtDNA) deletion. Clinical diagnoses included chronic progressive external ophthalmoplegia (94 patients); Kearns-Sayre syndrome (KSS; 33 patients); Pearson's marrow-pancreas syndrome (six patients); and Leigh syndrome, Reye-like syndrome, and mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (one patient). The length and location of deletion were highly variable. Only one patient had deletion within the so-called shorter arc between the two origins of mtDNA replication. The length of deletion and the number of deleted transfer ribonucleic acid (tRNAs) showed a significant relationship with age at onset. Furthermore, KSS patients had longer and larger numbers of deleted tRNAs, which could be risk factors for the systemic involvement of single mtDNA deletion diseases. We found 81 patterns of deletion. Direct repeats of 4 bp or longer flanking the breakpoints were found in 96 patients (70.5%) and those of 10 bp or longer in 49 patients (36.0%). We found two other common deletions besides the most common deletion (34 patients: 25.0%): the 2,310-bp deletion from nt 12113 to nt 14421 (11 patients: 8.0%) and the 7,664-bp deletion from nt 6330 to nt 13993 (ten patients: 7.3%). These deletions had incomplete direct repeats longer than 13 bp with one base mismatch.

Mitochondrial DNA Deletion in a Child With Mitochondrial Encephalomyopathy, Growth Hormone Deficiency, and Hypoparathyroidism

We report an 11-year-old boy with short stature, bilateral ptosis, sensorineural hearing loss, muscle weakness, and endocrine abnormalities. Brain magnetic resonance imaging (MRI) showed a bilateral abnormal signal in the globus pallidus and in the midbrain tegment. Muscle biopsy specimens showed ragged red and cytochrome c oxidase negative fibers, and biochemical analysis of muscle homogenate showed a partial defect of complex I and IV activities of the respiratory chain enzymes. Analysis of mitochondrial DNA by a polymerase chain reaction screening procedure and Southern blot revealed a novel heteroplasmic single mitochondrial DNA deletion of 7.8 kb in different tissues. This deletion was absent in the blood DNA of his mother and brother. This case further expands and confirms the wide clinical spectrum of mitochondrial disorders associated with single large-scale mitochondrial DNA deletions.

Congenital cataract as the first symptom of a neuromuscular disease caused by a novel single large-scale mitochondrial DNA deletion.

The male proband reported here was born with appropriate anthropometric parameters at term as the second child of healthy nonconsanguineous parents. His only clinical symptom was bilateral congenital cataracts with strabismus at birth, and both lenses were removed surgically at the age of 8 months. The perinatal and infantile period thereafter was clinically uneventful and his psychomotor development appeared almost normal. At the age of 6 years he was hospitalized for slight muscle weakness, minor ptosis, nystagmus and decreased physical activity. Soon after, his general condition worsened, gait ataxia presented, dysphagia and difficulty of speech followed by rapidly progressive generalized ataxia, and myopathy developed. Typical progressive gray matter degeneration with focal necrosis in the basal ganglia characteristic of the Leigh type of neuropathology could be detected by cranial MRI, the muscle histology showed ragged-red fibers. At the age of 7.5 years, unexpected left side hemiparesis with speech disability resembling that seen in MELAS syndrome developed, from which he recovered within 1.5 days. The mtDNA of the patient showed single 6.7 kb large-scale deletion harboring between 7817 and 14 536 bp. This case represents the first report of a verified mtDNA mutation associated with congenital cataracts as the first clinical sign of a later developing progressive neuromuscular disease presented with a combination of Leigh neuropathology, ragged-red fiber histopathology and stroke-like attack.

Clonal expansion of mitochondrial DNA with multiple deletions in autosomal dominant progressive external ophthalmoplegia.

Sporadic progressive external ophthalmoplegia and Kearns-Sayre syndrome are usually associated with single large-scale mitochondrial DNA deletions in muscle. In progressive external ophthalmoplegia with autosomal dominant inheritance, multiple mitochondrial DNA deletions have been reported. We studied several members of a Swedish family with autosomal dominant progressive external ophthalmoplegia and multiple mitochondrial DNA deletions by polymerase chain reaction analysis of single muscle fibers and by in situ hybridization, combined with enzyme histochemical analysis. Muscle fiber segments with deficiency of cytochrome c oxidase, which is partially encoded by mitochondrial DNA, had accumulated mitochondrial DNA with deletions and showed reduced levels of wild-type mitochondrial DNA. The deletions varied between individual muscle fibers. There was one predominant deletion in each cytochrome c oxidase-deficient muscle fiber segment. Sequencing of the deletion breakpoints showed that most but not all of the deletions were flanked by direct repeats. Young, clinically affected individuals of this family without limb muscle symptoms did not show mitochondrial DNA deletions or cytochrome c oxidase-deficient muscle fibers. Our results indicate that a nuclear factor predisposes to the development of somatic multiple mitochondrial DNA deletions. Mitochondrial DNA with multiple different deletions shows clonal expansion, which leads to mitochondrial myopathy with ragged-red fibers and muscle weakness.