Mitochondrial Neurogastrointestinal Encephalomyopathy Patients Research Articles

Lysosomal dysfunction and overload of nucleosides in thymidine phosphorylase deficiency of MNGIE

Inherited deficiency of thymidine phosphorylase (TP), encoded by TYMP, leads to a rare disease with multiple mitochondrial DNA (mtDNA) abnormalities, mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). However, the impact of TP deficiency on lysosomes remains unclear, which are important for mitochondrial quality control and nucleic acid metabolism. Muscle biopsy tissue and skin fibroblasts from MNGIE patients, patients with m.3243 A > G mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and healthy controls (HC) were collected to perform mitochondrial and lysosomal functional analyses. In addition to mtDNA abnormalities, compared to controls distinctively reduced expression of LAMP1 and increased mitochondrial content were detected in the muscle tissue of MNGIE patients. Skin fibroblasts from MNGIE patients showed decreased expression of LAMP2, lowered lysosomal acidity, reduced enzyme activity and impaired protein degradation ability. TYMP knockout or TP inhibition in cells can also induce the similar lysosomal dysfunction. Using lysosome immunoprecipitation (Lyso- IP), increased mitochondrial proteins, decreased vesicular proteins and V-ATPase enzymes, and accumulation of various nucleosides were detected in lysosomes with TP deficiency. Treatment of cells with high concentrations of dThd and dUrd also triggers lysosomal dysfunction and disruption of mitochondrial homeostasis. Therefore, the results provided evidence that TP deficiency leads to nucleoside accumulation in lysosomes and lysosomal dysfunction, revealing the widespread disruption of organelles underlying MNGIE.Graphical

Distinctive metabolic remodeling in TYMP deficiency beyond mitochondrial dysfunction.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the TYMP gene, which encodes thymidine phosphorylase (TP). As a cytosolic metabolic enzyme, TP defects affect biological processes that are thought to not be limited to the abnormal replication of mitochondrial DNA. This study aimed to elucidate the characteristic metabolic alterations and associated homeostatic regulation caused by TYMP deficiency. The pathogenicity of novel TYMP variants was evaluated in terms of clinical features, genetic analysis, and structural instability. We analyzed plasma samples from three patients with MNGIE; three patients with m.3243A > G mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); and four healthy controls (HC) using both targeted and untargeted metabolomics techniques. Transcriptomics analysis and bioenergetic studies were performed on skin fibroblasts from participants in these three groups. A TYMP overexpression experiment was conducted to rescue the observed changes. Compared with controls, specific alterations in nucleosides, bile acids, and steroid metabolites were identified in the plasma of MNGIE patients. Comparable mitochondrial dysfunction was present in fibroblasts from patients with TYMP deficiency and in those from patients with the m.3243A > G mutation. Distinctively decreased sterol regulatory element binding protein (SREBP) regulated cholesterol metabolism and fatty acid (FA) biosynthesis as well as reduced FA degradation were revealed in fibroblasts with TYMP deficiency. The restoration of thymidine phosphorylase activity rescued the observed changes in MNGIE fibroblasts. Our findings indicated that more widespread metabolic disturbance may be caused by TYMP deficiency in addition to mitochondrial dysfunction, which expands our knowledge of the biochemical outcome of TYMP deficiency. KEY MESSAGES: Distinct metabolic profiles in patients with TYMP deficiency compared to those with m.3243A > G mutation. TYMP deficiency leads to a global disruption of nucleoside metabolism. Cholesterol and fatty acid metabolism are inhibited in individuals with MNGIE. TYMP is functionally related to SREBP-regulated pathways. Potential metabolite biomarkers that could be valuable clinical tools to improve the diagnosis of MNGIE.

Distinctive gastrointestinal motor dysfunction in patients with MNGIE.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare mitochondrial disease caused by mutations in TYMP, encoding thymidine phosphorylase. Clinically it is characterized by severe gastrointestinal dysmotility associated with cachexia and a demyelinating sensorimotor polyneuropathy. Even though digestive manifestations are progressive and invariably lead to death, the features of gastrointestinal motor dysfunction have not been systematically evaluated. The objective of this study was to describe gastrointestinal motor dysfunction in MNGIE using state-of-the art techniques and to evaluate the relationship between motor abnormalities and symptoms. Prospective study evaluating gastrointestinal motor function and digestive symptoms in all patients with MNGIE attended at a national referral center in Spain between January 2018 and July 2022. In this period, five patients diagnosed of MNGIE (age range 16-46 years, four men) were evaluated. Esophageal motility by high-resolution manometry was abnormal in four patients (two hypoperistalsis, two aperistalsis). Gastric emptying by scintigraphy was mildly delayed in four and indicative of gastroparesis in one. In all patients, small bowel high-resolution manometry exhibited a common, distinctive dysmotility pattern, characterized by repetitive bursts of spasmodic contractions, without traces of normal fasting and postprandial motility patterns. Interestingly, objective motor dysfunctions were detected in the absence of severe digestive symptoms. MNGIE patients exhibit a characteristic motor dysfunction, particularly of the small bowel, even in patients with mild digestive symptoms and in the absence of morphological signs of intestinal failure. Since symptoms are not predictive of objective findings, early investigation is indicated.

Successful liver transplantation in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal disorder characterized by progressive gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, skeletal myopathy, ophthalmoparesis, and ptosis. MNGIE stems from deficient thymidine phosphorylase activity (TP) leading to toxic elevations of plasma thymidine. Hematopoietic stem cell transplant (HSCT) restores TP activity and halts disease progression but has high transplant-related morbidity and mortality. Liver transplant (LT) was reported to restore TP activity in two adult MNGIE patients. We report successful LT in four additional MNGIE patients, including a pediatric patient.Our patients were diagnosed between ages 14 months and 36 years with elevated thymidine levels and biallelic pathogenic variants in TYMP. Two patients presented with progressive gastrointestinal dysmotility, and three demonstrated progressive peripheral neuropathy with two suffering limitations in ambulation. Two patients, including the child, had liver dysfunction and cirrhosis.Following LT, thymidine levels nearly normalized in all four patients and remained low for the duration of follow-up. Disease symptoms stabilized in all patients, with some manifesting improvements, including intestinal function. No patient died, and LT appeared to have a more favorable safety profile than HSCT, especially when liver disease is present. Follow-up studies will need to document the long-term impact of this new approach on disease outcome.Take Home Message: Liver transplantation is effective in stabilizing symptoms and nearly normalizing thymidine levels in patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and may have an improved safety profile over hematopoietic stem cell transplant.

Alpha-1-Antitrypsin Promoter Improves the Efficacy of an Adeno-Associated Virus Vector for the Treatment of Mitochondrial Neurogastrointestinal Encephalomyopathy.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a devastating disease caused by mutations in TYMP, which encodes thymidine phosphorylase (TP). In MNGIE patients, TP dysfunction results in systemic thymidine and deoxyuridine overload, which interferes with mitochondrial DNA replication. Preclinical studies have shown that gene therapy using a lentiviral vector targeted to hematopoietic stem cells or an adeno-associated virus (AAV) vector transcriptionally targeted to liver are feasible approaches to treat MNGIE. Here, we studied the effect of various promoters (thyroxine-binding globulin [TBG], phosphoglycerate kinase [PGK], hybrid liver-specific promoter [HLP], and alpha-1-antitrypsin [AAT]) and DNA configuration (single stranded or self complementary) on expression of the TYMP transgene in the AAV8 serotype in a murine model of MNGIE. All vectors restored liver TP activity and normalized nucleoside homeostasis in mice. However, the liver-specific promoters TBG, HLP, and AAT were more effective than the constitutive PGK promoter, and the self-complementary DNA configuration did not provide any therapeutic advantage over the single-stranded configuration. Among all constructs, only AAV-AAT was effective in all mice treated at the lowest dose (5 × 1010 vector genomes/kg). As use of the AAT promoter will likely minimize the dose needed to achieve clinical efficacy as compared to the other promoters tested, we propose using the AAT promoter in the vector eventually designed for clinical use.

Transplantation, gene therapy and intestinal pathology in MNGIE patients and mice

BackgroundGastrointestinal complications are the main cause of death in patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). Available treatments often restore biochemical homeostasis, but fail to cure gastrointestinal symptoms.MethodsWe evaluated the small intestine neuromuscular pathology of an untreated MNGIE patient and two recipients of hematopoietic stem cells, focusing on enteric neurons and glia. Additionally, we evaluated the intestinal neuromuscular pathology in a mouse model of MNGIE treated with hematopoietic stem cell gene therapy. Quantification of muscle wall thickness and ganglion cell density was performed blind to the genotype with ImageJ. Significance of differences between groups was determined by two-tailed Mann-Whitney U test (P < 0.05).ResultsOur data confirm that MNGIE presents with muscle atrophy and loss of Cajal cells and CD117/c-kit immunoreactivity in the small intestine. We also show that hematopoietic stem cell transplantation does not benefit human intestinal pathology at least on short-term.ConclusionsWe suggest that hematopoietic stem cell transplantation may be insufficient to restore intestinal neuropathology, especially at later stages of MNGIE. As interstitial Cajal cells and their networks play a key role in development of gastrointestinal dysmotility, alternative therapeutic approaches taking absence of these cells into account could be required.

Mitochondrial Neurogastrointestinal Encephalomyopathy Caused by Thymidine Phosphorylase Enzyme Deficiency: From Pathogenesis to Emerging Therapeutic Options.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a progressive metabolic disorder caused by thymidine phosphorylase (TP) enzyme deficiency. The lack of TP results in systemic accumulation of deoxyribonucleosides thymidine (dThd) and deoxyuridine (dUrd). In these patients, clinical features include mental regression, ophthalmoplegia, and fatal gastrointestinal complications. The accumulation of nucleosides also causes imbalances in mitochondrial DNA (mtDNA) deoxyribonucleoside triphosphates (dNTPs), which may play a direct or indirect role in the mtDNA depletion/deletion abnormalities, although the exact underlying mechanism remains unknown. The available therapeutic approaches include dialysis and enzyme replacement therapy, both can only transiently reverse the biochemical imbalance. Allogeneic hematopoietic stem cell transplantation is shown to be able to restore normal enzyme activity and improve clinical manifestations in MNGIE patients. However, transplant related complications and disease progression result in a high mortality rate. New therapeutic approaches, such as adeno-associated viral vector and hematopoietic stem cell gene therapy have been tested in Tymp-/-Upp1-/- mice, a murine model for MNGIE. This review provides background information on disease manifestations of MNGIE with a focus on current management and treatment options. It also outlines the pre-clinical approaches toward future treatment of the disease.

Long-Term Restoration of Thymidine Phosphorylase Function and Nucleoside Homeostasis Using Hematopoietic Gene Therapy in a Murine Model of Mitochondrial Neurogastrointestinal Encephalomyopathy.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a metabolic disorder caused by mutations in TYMP, encoding thymidine phosphorylase (TP). In MNGIE patients, TP dysfunction produces systemic thymidine and deoxyuridine accumulation, which ultimately impairs mitochondrial DNA replication and results in mitochondrial dysfunction. To date, only allogeneic hematopoietic stem cell transplantation has demonstrated long-term clinical efficacy, but high morbidity and mortality associated with this procedure necessitate the search for safer alternatives. In a previous study, we demonstrated that hematopoietic stem cell gene therapy using a lentiviral vector containing the coding sequence of TYMP restored the biochemical homeostasis in an animal model of MNGIE. In the present follow-up study, we show that ectopic expression of TP in the hematopoietic system restores normal nucleoside levels in plasma, as well as in tissues affected in MNGIE such as small intestine, skeletal muscle, brain, and liver. Mitochondrial dNTP pool imbalances observed in liver of the animal model were also corrected by the treatment. The biochemical effects were maintained at least 20 months even with low levels of chimerism. No alterations in the blood cell counts or other toxic effects were observed in association with the lentiviral transduction or TP overexpression. These results further support the notion that gene therapy is a feasible treatment option for MNGIE.

279. Efficient and Safe Lentiviral Vector-Mediated Hematopoietic Stem Cell Gene Therapy in MNGIE Mice

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) patients are deficient in thymidine phosphorylase(TP) resulting in systemic thymidine(Thd) and deoxyuridine(dUrd) accumulation affecting mtDNA replication and causing mitochondrial dysfunction. Common symptoms are gastrointestinal dysmotility, progressive ophthalmoplegia and leukoencephalopathy. Allogenic hematopoietic stem cell (HSC) transplantation has been shown to reduce disease symptoms, but is not well tolerated due to the inherent toxicity of the procedure. Therefore, syngeneic ex vivo lentiviral vector HSC gene therapy overexpressing the native cDNA or the codon optimized (TPco) sequence driven by the phosphoglycerate kinase (PGK) or spleen focus forming virus (SFFV) promoters in Tp−/-Upp−/- double knockout mice, a model for MNGIE disease, was investigated. At 1 month post transplantation after sublethal total body irradiation, very low TP activity was detected in blood of control wild type mice (0.07±0.03nmoles/h/mg), but enzyme activities in PGK treated mice were at least 90-fold higher (PGK-TP = 150±4 and PGK-TPco = 96±4 nmoles/h/mg), and in SFFV recipient mice 400-fold higher (450±5 nmoles/h/mg). Consequently, a significant reduction of plasma and urine Thd and dUrd levels was observed. Long-term follow up (14 months) showed on average 1.2-fold wild type TP activity levels increase in LV-PGK-TP and LV-PGK-TPco and 36-fold in SFFV-TPco treated mice. This was sufficient for sustained reduction of plasma and urine nucleoside levels, which was achieved at 76.5±8.2% donor chimerism levels with low LV vector copy numbers (1.0±1.1VCN/donor cell). The LV integration profile in bone marrow cells of primary recipients was analyzed; LVs displayed the expected tendency to integrate within highly expressed genes and the integration pattern did not differ from that of other SIN-LV vectors in other disease models (primary immune deficiencies and lysosomal enzyme storage disorders). Overall, stem cell gene therapy provided stable TP expression and long-term biochemical correction in MNGIE mice without genotoxicity or apparent phenotoxicity, which will be further evaluated for somatic and neurological phenotype correction and optimized to develop a clinical protocol to treat MNGIE patients.

OP45 – 3024: Efficient lentiviral vector-mediated hematopoietic stem cell gene therapy in MNGIE mice

Objective Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) patients are deficient in thymidine phosphorylase (TP) resulting in systemic thymidine (Thd) and deoxyuridine (dUrd) accumulation affecting mtDNA replication and causing mitochondrial dysfunction. Common symptoms are gastrointestinal dysmotility, progressive ophthalmoplegia and leukoencephalopathy. Allogeneic hematopoietic stem cell (HSC) transplantation has been shown to reduce disease symptoms, but is not well tolerated due to the inherent toxicity of the procedure. Application of lentiviral vector therapy. Methods Therefore, syngeneic ex vivo lentiviral vector HSC gene therapy overexpressing the native cDNA or the codon optimized (TPco) sequence driven by the phosphoglycerate kinase (PGK) or spleen focus forming virus (SFFV) promoters in Tp-/-Upp-/- double knockout mice, a model for MNGIE disease, was investigated. Results At 1 month post transplantation after sublethal total body irradiation, very low TP activity was detected in blood of control wild type mice (0.07±0.03nmoles/h/mg), but enzyme activities in PGK treated mice were at least 90-fold higher (PGK-TP = 150±4 and PGK-TPco=96±4 nmoles/h/mg), compared to a 400-fold increase observed in SFFV recipient mice (450±5) and consequently, a significant reduction of plasma and urine Thd and dUrd levels was observed. Long-term follow up (14 months post treatment) showed on average 1.2-fold TP wild type activity levels in LV-PGK-TP and LV-PGK-TPco and 36-fold in SFFV-TPco treated mice, sufficient for sustained reduction of plasma and urine nucleoside levels, which was achieved at 76.5±8.2% donor chimerism levels with low LV vector copy numbers (1.0±1.1VCN/donor cell). Conclusion Overall, stem cell gene therapy provided stable TP expression and long-term biochemical correction in MNGIE mice without genotoxicity or apparent phenotoxicity, which will be further evaluated for somatic and neurological phenotype correction and optimized to develop a clinical protocol to treat MNGIE patients.

Thymidine phosphorylase is both a therapeutic and a suicide gene in a murine model of mitochondrial neurogastrointestinal encephalomyopathy.

Suicide gene therapy (SGT) is a promising strategy for treating cancer. In this work, we show that thymidine phosphorylase (TP) deficiency, the underlying genetic defect in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), presents an opportunity to apply SGT using capecitabine, a commonly used prodrug that is converted into 5-fluorouracil by TP. Using an immortalised B-lymphoblastoid cell line from a patient with MNGIE, the tumourigenic EL-4 cell line, lentiviral vectors encoding TP and a double knockout (Tymp(-/-)Upp1(-/-)) murine model, we found that EL-4 cell-derived TP(+) tumours were exquisitely sensitive to capecitabine and generated a significant local bystander effect. In addition, we detected a spontaneous cytolytic immune response in a significant fraction of the animals surviving more than 20 days after termination of the therapy. These data indicate that, in individuals lacking TP expression, TP is a highly specific suicide gene, which can be used to treat tumours that could hypothetically arise in MNGIE patients undergoing gene therapy, as these tumours will likely originate from the gene-modified cells and will be selectively targeted by capecitabine. These observations have important implications for gene therapy for MNGIE.

Liver as a source for thymidine phosphorylase replacement in mitochondrial neurogastrointestinal encephalomyopathy.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive mitochondrial disease associated with mutations in the nuclear TYMP gene. As a result, the thymidine phosphorylase (TP) enzyme activity is markedly reduced leading to toxic accumulation of thymidine and therefore altered mitochondrial DNA. MNGIE is characterized by severe gastrointestinal dysmotility, neurological impairment, reduced life expectancy and poor quality of life. There are limited therapeutic options for MNGIE. In the attempt to restore TP activity, allogenic hematopoietic stem cell transplantation has been used as cellular source of TP. The results of this approach on ∼20 MNGIE patients showed gastrointestinal and neurological improvement, although the 5-year mortality rate is about 70%. In this study we tested whether the liver may serve as an alternative source of TP. We investigated 11 patients (7M; 35–55 years) who underwent hepatic resection for focal disorders. Margins of normal liver tissue were processed to identify, quantify and localize the TP protein by Western Blot, ELISA, and immunohistochemistry, and to evaluate TYMP mRNA expression by qPCR. Western Blot identified TP in liver with a TP/GAPDH ratio of 0.9±0.5. ELISA estimated TP content as 0.5±0.07 ng/μg of total protein. TP was identified in both nuclei and cytoplasm of hepatocytes and sinusoidal lining cells. Finally, TYMP mRNA was expressed in the liver. Overall, our study demonstrates that the liver is an important source of TP. Orthotopic liver transplantation may be considered as a therapeutic alternative for MNGIE patients.

Gene Therapy Using a Liver-targeted AAV Vector Restores Nucleoside and Nucleotide Homeostasis in a Murine Model of MNGIE

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder caused by mutations in TYMP, enconding thymidine phosphorylase (TP). TP deficiency results in systemic accumulation of thymidine and deoxyuridine, which interferes with mitochondrial DNA (mtDNA) replication and leads to mitochondrial dysfunction. To date, the only treatment available for MNGIE patients is allogeneic hematopoietic stem cell transplantation, which is associated with high morbidity and mortality. Here, we report that AAV2/8-mediated transfer of the human TYMP coding sequence (hcTYMP) under the control of a liver-specific promoter prevents the biochemical imbalances in a murine model of MNGIE. hcTYMP expression was restricted to liver, and a dose as low as 2 × 10(11) genome copies/kg led to a permanent reduction in systemic nucleoside levels to normal values in about 50% of treated mice. Higher doses resulted in reductions to normal or slightly below normal levels in virtually all mice treated. The nucleoside reduction achieved by this treatment prevented deoxycytidine triphosphate (dCTP) depletion, which is the limiting factor affecting mtDNA replication in this disease. These results demonstrate that the use of AAV to direct TYMP expression in liver is feasible as a potentially safe gene therapy strategy for MNGIE.

HPLC-UV analysis of thymidine and deoxyuridine in plasma of patients with thymidine phosphorylase deficiency

We present a simple, fast and validated method for the determination of the two nucleosides thymidine (dThd) and deoxyuridine (dUrd) in plasma of patients with symptoms suggestive of mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), using high performance liquid chromatography coupled with ultraviolet spectrophotometric detection (HPLC-UV). Plasma sample (100μL) pretreatment was based on simple deproteinization by 1.2M perchloric acid, using theophylline as internal standard (I.S.). HPLC-UV analysis was carried out on a Synergi 4μm Hydro-RP, 150×4mm I.D. column, at room temperature. The mobile phase was a mixture of potassium dihydrogen phosphate buffer (20mM, pH 4.5) and acetonitrile (95:5, v/v), at an isocratic flow rate of 0.7mL/min. The UV detector was set at 267nm. The chromatographic run lasted 19min. Similar pyrimidine nucleotides and nucleosides do not interfere with the assay. Calibration curves were linear for both dThd and dUrd over a range of 0.5 to 5.0μg/mL. The limit of quantitation was 0.5μg/mL for both nucleosides and the absolute recovery was >90% for dThd, dUrd and the I.S. Both intra- and inter-assay precision and accuracy were lower than 10% at all tested concentrations. The proposed method was successfully applied to measure plasma concentrations of dThd and dUrd in two MNGIE patients. This assay simplifies both plasma pretreatment and chromatographic conditions of previously reported procedures and describes the first validated method for the determination of the two nucleotides in human plasma.

The Role of Brain MRI in Mitochondrial Neurogastrointestinal Encephalomyopathy

Leukoencephalopathy is a hallmark of mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) a devastating disorder characterized by ptosis, ophthalmoparesis, gastrointestinal dysfunction and polyneuropathy. To characterize MNGIE-associated leukoencephalopathy and to correlate it with clinical, biochemical and molecular data, four MNGIE patients with heterogeneous clinical phenotypes (enteropathic arthritis, exercise intolerance, CIDP-like phenotype and typical presentation) were studied by magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). Diffusion weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps were also obtained. In two patients we also investigated the role of brain MRI in monitoring the evolution of leukoencephalopathy by performing follow-up imaging studies at an interval of one and two years. The extension and distribution of leukoencephalopathy were not clearly linked with age, phenotype or disease severity, and did not seem to be related to TYMP mutations, enzyme activity or pyrimidine levels. In the studied patients MRS revealed reduced N-acetyl-aspartate and increased choline signals. Although DWI appeared normal in all patients but one, ADC maps always showed moderate increased diffusivity. Leukoencephalopathy worsened over a two-year period in two patients, regardless of the clinical course, indicating a lack of correlation between clinical phenotype, size and progression of white matter abnormalities during this period. Brain MRI should be considered a very useful tool to diagnose both classical and atypical MNGIE. Serial MRIs in untreated and treated MNGIE patients will help to establish whether the leukoencephalopathy is a reversible condition or not.

Possible toxicity of tuberculostatic agents in a patient with a novel TYMP mutation leading to mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive multisystemic disorder caused by TYMP gene mutations. Here, we report on the first MNGIE patient diagnosed in Bulgaria who carries a novel homozygous TYMP mutation (p.Leu347Pro). The patient presented with gastrointestinal complaints, cachexia, hearing loss, ptosis, ophthalmoparesis, polyneuropathy, cognitive impairment and leukoencephalopathy on MRI examination of the brain. The patient´s motor capacity declined significantly leading to wheelchair dependence several months following the administration of tuberculostatic treatment suggesting mitochondrial toxicity of these agents.

Compound heterozygous mutations of TYMP as underlying causes of mitochondrial neurogastrointestinal encephalomyopathy (MNGIE)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), an autosomal recessive multiorgan disease, frequently associated with mutations in the thymidine phosphorylase (TYMP) gene. TYMP encodes thymidine phosphorylase (TP), which has an essential role in the nucleotide salvage pathway for mitochondrial DNA (mtDNA) replication. This study reports an MNGIE patient with novel compound heterozygous missense mutations (Thr151Pro and Leu270Pro) in TYMP. Each mutation was inherited from one parent. Neither mutation was found in the controls and the mutation sites were well conserved between different species. Neither large deletion nor causative point mutations were found in the mtDNA. The patient presented with MNGIE symptoms, including gastrointestinal discomfort, external ophthalmoplegia, pigmentary retinopathy and demyelinating type diffuse sensory motor polyneuropathy. The patient demonstrated an early-onset but mild phenotype, with 9.6%TP activity; therefore, patients with these compound heterozygous mutations may exhibit a mild phenotype with a variable onset age according to TP activity level.

Course and management of allogeneic stem cell transplantation in patients with mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder caused by mutations in the gene encoding thymidine phosphorylase (TP). Allogeneic hematopoietic stem cell transplantation (HSCT) has been proposed as a treatment for patients with MNGIE and a standardized approach to HSCT in this condition has recently been developed. We report on the transplant course, management and short-term follow-up in two MNGIE patients who underwent HSCT. The source of stem cells was bone marrow taken from an HLA 9/10 allele-matched unrelated donor in the first patient and from an HLA 10/10 allele-matched sibling donor in the second. Both patients achieved full donor chimerism, and we observed restoration of buffy coat TP activity and lowered urine nucleoside concentrations in both of them. The post-transplant clinical follow-up showed improvement in gastrointestinal dysmotility, abdominal cramps and diarrhea. Neurological assessment remained unchanged. However, the first patient died 15 months after HSCT due to gastrointestinal obstruction and shock; the second patient died 8 months after the procedure due to respiratory distress following septic shock. Although HSCT corrects biochemical abnormalities and improves gastrointestinal symptoms, the procedure can be risky in subjects already in poor medical condition as are many MNGIE patients. Since transplant-related morbidity and mortality increases with progression of the disease and number of comorbidities, MNGIE patients should be submitted to HSCT when they are still relatively healthy, in order to minimize the complications of the procedure. Anyway, there is still incomplete knowledge on the natural history of the disease in many affected patients and it is not yet clear when the best time to do a transplant is. Further clues to the therapeutic potential of HSCT could result from a prolonged observation in a greater number of non-transplanted and transplanted patients, which would allow us to answer the questions of if, how and when MNGIE patients require HSCT treatment.

Mitochondrial neurogastrointestinal encephalopathy in an Indian family with possible manifesting carriers of heterozygous TYMP mutation

Background Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a distinctive autosomal recessive disorder with mitochondrial alterations due to mutations TYMP gene encoding thymidine phosphorylase. Materials and methods Study of clinical and biochemical characteristics of a family with MNGIE. Results Index case was a 32 year old man presenting with recurrent vomiting, early satiety and progressive weight loss. He had ptosis, restricted eye movements, generalized muscle wasting, and absent tendon reflexes. Lactate levels were elevated in venous blood and CSF lactate. MRI brain showed diffuse leucoencephalopathy. Barium swallow showed near total obstruction at mid portion of vertical limb of duodenum with ileus. Esophageal manometry suggested myopathy. Muscle biopsy revealed moderate numbers of ragged blue and ragged red fibers as well as cytochrome c oxidase deficient fibers. An elder brother had similar symptoms and expired after a surgical procedure and a 28 year old brother has similar illness. The father had asymptomatic bilateral ptosis with mild ophthalmoparesis. The paternal grandfather and paternal aunt also had bilateral ptosis. Clinical diagnosis of MNGIE was confirmed in the two living brothers by demonstrating severe defects of thymidine phosphorylase activity in buffy coat, elevated thymidine and deoxyuridine in plasma, and a homozygous TYMP c.893 G > A mutation. Conclusions This family with biochemically and genetically confirmed mitochondrial neurogastrointestinal encephalopathy syndrome uncharacteristically included heterozygous TYMP mutation carriers manifesting extra-ocular weakness. It is important to identify MNGIE patients early because therapeutic options are emerging.

Pitfalls in diagnosing mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder caused by mutations in the gene encoding thymidine phosphorylase and is characterized by external ophthalmoparesis, gastrointestinal dysmotility, leukoencephalopathy, and neuropathy. The availability of new therapeutic options (peritoneal dialysis, allogeneic stem cell transplantation, enzyme replacement) makes it necessary to diagnose the disease early, which is not always achieved due to the difficulty in recognizing this disorder, especially in case of atypical presentation. We describe three MNGIE patients with atypical onset of the disease. In the first patient the main symptoms were long-standing chronic fever, recurrent acute migrant arthritis, and gastrointestinal disorders mimicking autoimmune or inflammatory intestinal diseases; the second patient complained only of exercise intolerance and muscle cramps, and the third patient had a CIDP-like polyneuropathy. This study stresses the insidious heterogeneous clinical onset of some cases of MNGIE, expands the spectrum of the phenotype, and suggests considering MNGIE in the differential diagnosis of enteropathic arthritis, isolated exercise intolerance, and inflammatory polyneuropathies not responsive to the usual treatment. A better understanding of the clinical heterogeneity of MNGIE is necessary in order to diagnose atypical cases and promote early diagnosis, which is now absolutely necessary in view of the new available therapies.