Successful Sequential Liver and Isolated Intestine Transplantation for Mitochondrial Neurogastrointestinal Encephalopathy Syndrome: A Case Report.

BACKGROUND Mitochondrial neurogastrointestinal encephalopathy syndrome (MNGIE) is an autosomal recessive disease caused by thymidine phosphorylase deficiency leading to progressive gastrointestinal dysmotility, cachexia, ptosis, ophthalmoparesis, peripheral neuropathy and leukoencephalopathy. Although liver transplantation corrects thymidine phosphorylase deficiency, intestinal deficiency of the enzyme persists. Retrospective chart review was carried out to obtain clinical, biochemical, and pathological details. CASE REPORT We present a case of liver and subsequent intestine transplant in a 28-year-old man with MNGIE syndrome with gastrointestinal dysmotility, inability to walk, leukoencephalopathy, ptosis, cachexia, and elevated serum thymidine. To halt progression of neurologic deficit, he first received a left-lobe partial liver transplantation. Although his motor deficit improved, gastrointestinal dysmotility persisted, requiring total parenteral nutrition. After exhaustive intestinal rehabilitation, he was listed for intestine transplantation. Two-and-half years after liver transplantation, he received an intestine transplant. At 4 years after LT and 20 months after the intestine transplant, he remains off parenteral nutrition and is slowly gaining weight. CONCLUSIONS This is the first reported case of mitochondrial neurogastrointestinal encephalomyopathy to undergo successful sequential liver and intestine transplantation.

Phenotype, genotype, and management of congenital fibrosis of extraocular muscles type 1 in 16 Chinese families.

PURPOSE: Congenital fibrosis of extraocular muscles type 1 (CFEOM1), a classical subtype of CFEOM, is characterized by restrictive ophthalmoplegia and ptosis. It is mainly caused by aberrant neural innervation of the extraocular muscles. This study aimed to investigate the genetic characteristics and clinical manifestations of CFEOM1 in Chinese families. METHODS: The clinical data, including ocular examinations, magnetic resonance imaging (MRI), and surgical procedures of affected individuals from 16 Chinese CFEOM1 families, were collected. The genomic DNA of 16 probands and their family members were sequenced for causative KIF21A gene mutations. Linkage analysis using microsatellite markers across KIF21A was also conducted. RESULTS: Affected individuals were presented with bilateral non-progressive ptosis, restricted horizontal eye movement, fixed infraduction of both eyes, compensatory chin-up head position, and neuromuscular abnormalities. Three heterozygous KIF21A mutations, c.2860C > T (p.R954W) (in eight families), c.2861G > T (p.R954L) (in two families), and c.2861G > A (p.R954Q) (in two families) were identified, which implied that hotspot mutations were common in Chinese CFEOM1 families. Germline Mosaicism was likely to be the cause of affected individuals with asymptomatic parents without KIF21A mutations presented in the eight families. Two affected individuals underwent modified levator muscle complex suspension surgery and achieved a good result without any complications. CONCLUSION: Instead of evaluating the whole CFEOM1 gene variant, hotspot mutations could be given priority for screening. The occurrence of germline mosaicism has to be taken into account in genetic counseling. Patients with CFEOM1 who have ptosis may benefit from an innovative surgical procedure called modified levator muscle complex suspension.

Mitochondrial neurogastrointestinal encephalomyopathy in a Pakistani female: a case report.

BACKGROUND: Mitochondrial neurogastrointestinal encephalopathy is a rare multisystem autosomal recessive disease caused by mutations in the TYMP gene, that encodes for thymidine phosphorylase. Mitochondrial neurogastrointestinal encephalopathy is a progressive degenerative disease characterized by a distinctive tetrad of gastrointestinal dysmotility, peripheral neuropathy, ophthalmoplegia with ptosis, and asymptomatic leukoencephalopathy. It provides a diagnostic dilemma to physicians in regions like Pakistan because of a lack of genetic study availability and associated financial constraints of the population. However, with careful examination and a few basic investigations, mitochondrial neurogastrointestinal encephalopathy can be diagnosed by ruling out most of the close differentials. CASE PRESENTATION: We report the case of a 23-year-old Asian female whose chief complaints were epigastric pain, bilious emesis, weight loss for 3 months, and bilateral lower limb weakness for 20 days. All clinical signs and symptoms along with relevant investigations including nerve conduction studies, electromyography, and magnetic resonance imaging of the brain were highly suggestive of mitochondrial neurogastrointestinal encephalopathy syndrome. Because of financial constraints, genetic studies could not be performed. The patient was managed with a multidisciplinary approach involving gastroenterology, physiotherapy, and nutrition departments. Currently, therapeutic options for the disease include allogeneic hematopoietic stem cell transplant and carrier erythrocyte entrapped thymidine phosphorylase; however, these could not be provided to the patient owing to certain limitations. CONCLUSIONS: As misdiagnosis and delayed diagnosis are quite common in this disease, the prime objective of this case report is to increase the basic understanding of this disease, especially its signs and symptoms, and address the limitations regarding the diagnostic investigations and management of patients with mitochondrial neurogastrointestinal encephalopathy.

Circulating miRNAs as Biomarkers for Mitochondrial Neuro-Gastrointestinal Encephalomyopathy.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare disease for which there are currently no validated outcome measures for assessing therapeutic intervention efficacy. The aim of this study was to identify a plasma and/or serum microRNA (miRNA) biomarker panel for MNGIE. Sixty-five patients and 65 age and sex matched healthy controls were recruited and assigned to one of four study phases: (i) discovery for sample size determination; (ii) candidate screening; (iii) candidate validation; and (iv) verifying the performance of the validated miRNA panel in four patients treated with erythrocyte-encapsulated thymidine phosphorylase (EE-TP), an enzyme replacement under development for MNGIE. Quantitative PCR (qPCR) was used to profile miRNAs in serum and/or plasma samples collected for the discovery, validation and performance phases, and next generation sequencing (NGS) analysis was applied to serum samples assigned to the candidate screening phase. Forty-one differentially expressed candidate miRNAs were identified in the sera of patients (p < 0.05, log2 fold change > 1). The validation cohort revealed that of those, 27 miRNAs were upregulated in plasma and three miRNAs were upregulated in sera (p < 0.05). Through binary logistic regression analyses, five plasma miRNAs (miR-192-5p, miR-193a-5p, miR-194-5p, miR-215-5p and miR-34a-5p) and three serum miRNAs (miR-192-5p, miR-194-5p and miR-34a-5p) were shown to robustly distinguish MNGIE from healthy controls. Reduced longitudinal miRNA expression of miR-34a-5p was observed in all four patients treated with EE-TP and coincided with biochemical and clinical improvements. We recommend the inclusion of the plasma exploratory miRNA biomarker panel in future clinical trials of investigational therapies for MNGIE; it may have prognostic value for assessing clinical status.

Novel Mutations of the TYMP Gene in Mitochondrial Neurogastrointestinal Encephalomyopathy: Case Series and Literature Review.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a multi-system disorder caused by several homozygous or compound heterozygous mutations, mostly in the nuclear gene of TYMP. Our current knowledge on the underlying pathology of the disease is derived through the study of about 200 cases of different ethnicities. Clinical presentations include severe cachexia, weakness, ptosis, diplopia, abdominal cramps or digestive tract disorders, hearing impairment, and paresthesia.Herein, we aim to present five novel mutations of the nuclear gene of TYMP in six Iranian patients diagnosed with MNGIE. In our population, age at the time of diagnosis was 18 to 49 years, while the onset of the symptoms varied from 13 to 20 years. We detected two pathogenic non-frameshift nonsense premature stop codon mutations (c.1013C > A, and c.130C > T), one variant of uncertain significance (VUS) non-frameshift missense mutation (c.345G > T), one likely pathogenic frameshift insertion (c.801_802insCGCG), and one likely benign homozygous non-frameshift deletion (c.1176_1187del) from two siblings. Our findings also confirm the autosomal recessive inheritance pattern of MNGIE in the Iranian population. The lack of knowledge in the area of nuclear gene-modifier genes shadows the genotype-phenotype relationships of MNGIE.

Evidence of enteric angiopathy and neuromuscular hypoxia in patients with mitochondrial neurogastrointestinal encephalomyopathy.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive disease caused by thymidine phosphorylase (TP) enzyme defect. As gastrointestinal changes do not revert in patients undergone TP replacement therapy, one can postulate that other unexplored mechanisms contribute to MNGIE pathophysiology. Hence, we focused on the local TP angiogenic potential that has never been considered in MNGIE. In this study, we investigated the enteric submucosal microvasculature and the effect of hypoxia on fibrosis and enteric neurons density in jejunal full-thickness biopsies collected from patients with MNGIE. Orcein staining was used to count blood vessels based on their size. Fibrosis was assessed using the Sirius Red and Fast Green method. Hypoxia and neoangiogenesis were determined via hypoxia-inducible-factor-1α (HIF-1α) and vascular endothelial cell growth factor (VEGF) protein expression, respectively. Neuron-specific enolase was used to label enteric neurons. Compared with controls, patients with MNGIE showed a decreased area of vascular tissue, but a twofold increase of submucosal vessels/mm2 with increased small size and decreased medium and large size vessels. VEGF positive vessels, fibrosis index, and HIF-1α protein expression were increased, whereas there was a diminished thickness of the longitudinal muscle layer with an increased interganglionic distance and reduced number of myenteric neurons. We demonstrated the occurrence of an angiopathy in the GI tract of patients with MNGIE. Neoangiogenetic changes, as detected by the abundance of small size vessels in the jejunal submucosa, along with hypoxia provide a morphological basis to explain neuromuscular alterations, vasculature breakdown, and ischemic abnormalities in MNGIE.NEW & NOTEWORTHY Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is characterized by a genetically driven defect of thymidine phosphorylase, a multitask enzyme playing a role also in angiogenesis. Indeed, major gastrointestinal bleedings are life-threatening complications of MNGIE. Thus, we focused on jejunal submucosal vasculature and showed intestinal microangiopathy as a novel feature occurring in this disease. Notably, vascular changes were associated with neuromuscular abnormalities, which may explain gut dysfunction and help to develop future therapeutic approaches in MNGIE.

Hematopoietic stem cell transplantation for mitochondrial neurogastrointestinal encephalopathy: A single-center experience underscoring the multiple factors involved in the prognosis.

BACKGROUND: Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a progressive autosomal recessive disorder characterized by cachexia, gastrointestinal (GI) dysmotility, ptosis, peripheral neuropathy, and brain magnetic resonance imaging (MRI) white matter changes. Bi-allelic TYMP mutations lead to deficient thymidine phosphorylase (TP) activity, toxic accumulation of plasma nucleosides (thymidine and deoxyuridine), nucleotide pool imbalances, and mitochondrial DNA (mtDNA) instability. Death is mainly due to GI complications: intestinal perforation, peritonitis, and/or liver failure. Based on our previous observations in three patients with MNGIE that platelet infusions resulted in a transient 40% reduction of plasma nucleoside levels, in 2005 we performed the first hematopoietic stem cell transplantation (HSCT) worldwide as a life-long source of TP in a patient with MNGIE. PROCEDURE: HSCT was performed in a total of six patients with MNGIE. The multiple factors involved in the prognosis of this cohort were analyzed and compared to the literature experience. RESULTS: Cell source was bone marrow in five patients and peripheral stem cells in one, all from fully human leukocyte antigen (HLA)-matched related donors, including four who were TYMP mutation carriers. Four of six (66%) survived compared to the 37% survival rate in the literature. Reduced intensity conditioning regimen contributed to secondary graft failure in two patients. Fifteen years post HSCT, the first transplanted patient is seemingly cured. Severe GI symptoms before transplantation were mostly irreversible and were poor prognostic factors. CONCLUSIONS: Allogenic HSCT could constitute a curative therapeutic option for carefully selected, young, presymptomatic, or mildly affected patients. Timing, donor selection, and optimal conditioning protocol are major determinants of outcome. HSCT is inadvisable in patients with advanced MNGIE disease.

Polyneuropathy Reveals Origins of Decade-long Gastrointestinal Symptoms in a Patient With Undiagnosed Mitochondrial Neurogastrointestinal Encephalopathy Caused by a Novel Mutation.

Mitochondrial neurogastrointestinal encephalopathy (MNGIE) is a rare autosomal recessive disease that manifests with multiorgan presentation characterized by gastrointestinal, extraocular, and both peripheral and central nervous system involvement. MNGIE is caused by mutation in the TYMP (thymidine phosphorylase) gene, resulting in loss of thymidine phosphorylase enzyme activity. This causes its substrates, thymidine and deoxyuridine, to accumulate in tissues and plasma, while also causing secondary alterations in mitochondrial DNA. To date, more than 80 mutations have been reported in this gene. We present herein the clinical, neuroimaging, electrodiagnostic, and molecular findings of a patient with MNGIE caused by a novel homozygous missense mutation (C1175T > G) of the TYMP gene.

Efficacy of adeno-associated virus gene therapy in a MNGIE murine model enhanced by chronic exposure to nucleosides.

BACKGROUND: Preclinical studies have shown that gene therapy is a feasible approach to treat mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). However, the genetic murine model of the disease (Tymp/Upp1 double knockout, dKO) has a limited functional phenotype beyond the metabolic imbalances, and so the studies showing efficacy of gene therapy have relied almost exclusively on demonstrating correction of the biochemical phenotype. Chronic oral administration of thymidine (dThd) and deoxyuridine (dUrd) to dKO mice deteriorates the phenotype of the animals, providing a better model to test therapy approaches. METHODS: dKO mice were treated with both dThd and dUrd in drinking water from weaning until the end of the study. At 8 - 11 weeks of age, mice were treated with several doses of adeno-associated virus (AAV) serotype 8 vector carrying the human TYMP coding sequence under the control of different liver-specific promoters (TBG, AAT, or HLP). The biochemical profile and functional phenotype were studied over the life of the animals. FINDINGS: Nucleoside exposure resulted in 30-fold higher plasma nucleoside levels in dKO mice compared with non-exposed wild type mice. AAV-treatment provided elevated TP activity in liver and lowered systemic nucleoside levels in exposed dKO mice. Exposed dKO mice had enlarged brain ventricles (assessed by magnetic resonance imaging) and motor impairment (rotarod test); both were prevented by AAV treatment. Among all promoters tested, AAT showed the best efficacy. INTERPRETATION: Our results show that AAV-mediated gene therapy restores the biochemical homeostasis in the murine model of MNGIE and, for the first time, demonstrate that this treatment improves the functional phenotype. FUNDING: This work was funded in part by the Spanish Instituto de Salud Carlos III, and the Generalitat de Catalunya. The disclosed funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The natural history of infantile mitochondrial DNA depletion syndrome due to RRM2B deficiency.

PURPOSE: Mitochondrial DNA (mtDNA) depletion syndrome (MDDS) encompasses a group of genetic disorders of mtDNA maintenance. Mutation of RRM2B is an uncommon cause of infantile-onset encephalomyopathic MDDS. Here we describe the natural history of this disease. METHODS: Multinational series of new genetically confirmed cases from six pediatric centers. RESULTS: Nine new cases of infantile-onset RRM2B deficiency, and 22 previously published cases comprised a total cohort of 31 patients. Infants presented at a mean of 1.95 months with truncal hypotonia, generalized weakness, and faltering growth. Seizures evolved in 39% at a mean of 3.1 months. Non-neurological manifestations included respiratory distress/failure (58%), renal tubulopathy (55%), sensorineural hearing loss (36%), gastrointestinal disturbance (32%), eye abnormalities (13%), and anemia (13%). Laboratory features included elevated lactate (blood, cerebrospinal fluid (CSF), urine, magnetic resonance (MR), spectroscopy), ragged-red and cytochrome c oxidase-deficient fibers, lipid myopathy, and multiple oxidative phosphorylation enzyme deficiencies in skeletal muscle. Eight new RRM2B variants were identified. Patients with biallelic truncating variants had the worst survival. Overall survival was 29% at 6 months and 16% at 1 year. CONCLUSIONS: Infantile-onset MDDS due to RRM2B deficiency is a severe disorder with characteristic clinical features and extremely poor prognosis. Presently management is supportive as there is no effective treatment. Novel treatments are urgently needed.

Whole exome sequencing reveals two novel compound heterozygous mutations in TWNK as a cause of the hepatocerebral form of mitochondrial DNA depletion syndrome: a case report.

BACKGROUND: Although Mitochondrial DNA depletion syndrome (MDS) can be classified into three forms: myopathic, encephalomyopathic and hepatocerebral form, it is difficult to identify its form due to its clinical heterogeneity. Therefore, it is very important to conduct molecular genetic analysis on suspected patients. This study presented a male 38 weeks and 5 days infant with liver cytolysis and leukodystrophy. CASE PRESENTATION: A male infant proband was admitted to the department of NICU for feeding intolerance, irregular rhythm of respiration, hypoglycemia, lactic acidosis, liver cytolysis and neurological abnormalities. He was onset of mild jaundice with leukodystrophy and high lactate and phenylderivatives for urine organic acids on the 7th day. Whole exome sequencing (WES) and Sanger sequencing were performed to screen and confirm the suspicious pathogenic mutations. The results revealed this proband carried two compound heterozygous mutations in TWNK: c.1186 C > T / p.Pro396Ser and c.1844 G > C / p.Gly615Ala inherited by an autosomal recessive form from his parents, of which protein conservative analysis and structural modeling supported the pathogenicity of the two mutations. Unfortunately, the conditions described above were not improved until he was discharged from the hospital on the 23rd day and died at 4 months of age. CONCLUSIONS: In this study, we investigated a Chinese family with the hepatocerebral form of MDS and conducted WES and Sanger sequencing to explore the causative mutations for this proband born from non-consanguineous and healthy parents. We identified two novel TWNK c.1186 C > T/ c.1844 G > C compound heterozygous mutations which were probably the disease-causing mutations of hepatocerebral form of MDS and described the clinical manifestations of the proband, which expanded the phenotypic spectrum of MDS caused by variants in TWNK. This study also emphasized WES technology can provide the genetic diagnosis of Mendelian genetic disease.

Genetic neuromuscular disorders: living the era of a therapeutic revolution. Part 1: peripheral neuropathies.

Recent advances in pathophysiological and genetic mechanisms of some neuromuscular diseases and a rapid progress in new pharmacological technologies led to an accelerated development of innovative treatments, generating an unexpected therapeutic revolution. In part 1, we report already commercially available drugs, just approved drugs and new therapeutic promises in the treatment of peripheral neuropathies. Hereditary transthyretin amyloidosis (hATTR) is a devastating disease due to amyloid accumulation in peripheral nerves, heart and autonomic system. The first specific drug approved for hATTR was tafamidis, a TTR tetramer stabilizer. In 2018, the positive results of two phase 3 trials have been reported leading to start of regulatory approval route for inotersen, an antisense oligonucleotide and patisiran, the first-ever RNA interference (RNAi) therapeutic. System biology targeting approach has indicated baclofen, naltrexone and sorbitol in combination (PXT3003) as candidate drugs for Charcot-Marie-Tooth disease type 1A. This hypothesis was confirmed in experimental models and in phase 2 and 3 clinical trials. Givosiran, another RNAi therapeutic, targeting 5-aminolevulinic acid synthase, has been positively tested in acute intermittent porphyria in phase 1/2 and ongoing phase 3 trials. Although allogenic hematopoietic stem cell transplantation resulted recently a long-term therapy in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), a new strategy is liver transplantation which is able to revert the severe biochemical and clinical imbalance of the disease. Recently, a gene therapy has been tested in a MNGIE murine model, indicating that it may become a new therapeutic option.

Outcome of inferior oblique disinsertion versus myectomy in the surgical treatment of unilateral congenital superior oblique palsy.

PURPOSE: To compare the outcome of inferior oblique disinsertion and myectomy in patients with unilateral congenital superior oblique palsy. METHODS: In this prospective study, consecutive patients with superior oblique palsy underwent either myectomy or disinsertion of the inferior oblique muscle. Success was defined as postoperative hypertropia of ≤5Δ in primary position and no hypotropia. In cases with preoperative hypertropia of ≤5Δ, success was defined as improved hypertropia and resolution of abnormal head position (AHP). RESULTS: A total of 62 patients were included: 34 underwent myectomy; 28, disinsertion. Preoperative primary position hypertropia was 15.8Δ ± 7.4Δ in the myectomy group and 14.5Δ ± 7.3Δ in the disinsertion (P = 0.756). AHP was present in 85.3% and 85.7% of patients, respectively (P = 1). Mean follow-up was in the myectomy group 7.5 ± 6.7 months and 6.9 ± 3.0 months in the disinsertion group (P = 0.637). Correction of hypertropia in primary position was more pronounced in the myectomy group (14.3Δ ± 7.4Δ vs 10.0Δ ± 5.4Δ; P = 0.013). Success was achieved in 91.2% of myectomy and 60.7% of disinsertion patients (P = 0.006). Persistence of AHP did not differ between groups (8.8% in the myectomy group vs 7.1% in the disinsertion group [P = 1]). Comparison of patients with preoperative hypertropia of ≤15Δ revealed nonsignificant differences between groups in rate of success (100% vs 81.3% [P = 0.226]) and correction of primary position hypertropia (8.8Δ ± 3.2Δ vs 7.6Δ ± 4.0Δ [P = 0.336]). CONCLUSIONS: In our study cohort, inferior oblique myectomy had a greater effect in reduction of primary position hypertropia; however, disinsertion proved as effective as myectomy if preoperative vertical deviation was ≤15Δ. Both procedures effectively corrected AHP and demonstrated self-adjustment.

Recessive mutations in muscle-specific isoforms of FXR1 cause congenital multi-minicore myopathy.

FXR1 is an alternatively spliced gene that encodes RNA binding proteins (FXR1P) involved in muscle development. In contrast to other tissues, cardiac and skeletal muscle express two FXR1P isoforms that incorporate an additional exon-15. We report that recessive mutations in this particular exon of FXR1 cause congenital multi-minicore myopathy in humans and mice. Additionally, we show that while Myf5-dependent depletion of all FXR1P isoforms is neonatal lethal, mice carrying mutations in exon-15 display non-lethal myopathies which vary in severity depending on the specific effect of each mutation on the protein.

Gastrointestinal Dysmotility in MNGIE: from thymidine phosphorylase enzyme deficiency to altered interstitial cells of Cajal.

BACKGROUND: MNGIE is a rare and fatal disease in which absence of the enzyme thymidine phosphorylase induces systemic accumulation of thymidine and deoxyuridine and secondary mitochondrial DNA alterations. Gastrointestinal (GI) symptoms are frequently reported in MNGIE patients, however, they are not resolved with the current treatment interventions. Recently, our understanding of the GI pathology has increased, which rationalizes the pursuit of more targeted therapeutic strategies. In particular, interstitial cells of Cajal (ICC) play key roles in GI physiology and are involved in the pathogenesis of the GI dysmotility. However, understanding of the triggers of ICC deficits in MNGIE is lacking. Herein, we review the current knowledge about the pathology of GI dysmotility in MNGIE, discuss potential mechanisms in relation to ICC loss/dysfunction, remark on the limited contribution of the current treatments, and propose intervention strategies to overcome ICC deficits. Finally, we address the advances and new research avenues offered by organoids and tissue engineering technologies, and propose schemes to implement to further our understanding of the GI pathology and utility in regenerative and personalized medicine in MNGIE. CONCLUSION: Interstitial cells of Cajal play key roles in the physiology of the gastrointestinal motility. Evaluation of their status in the GI dysmotility related to MNGIE would be valuable for diagnosis of MNGIE. Understanding the underlying pathological and molecular mechanisms affecting ICC is an asset for the development of targeted prevention and treatment strategies for the GI dysmotility related to MNGIE.

Next generation sequencing in family with MNGIE syndrome associated to optic atrophy: Novel homozygous POLG mutation in the C-terminal sub-domain leading to mtDNA depletion.

INTRODUCTION: Mitochondrial diseases are a group of disorders caused mainly by the impairment of the mitochondrial oxidative phosphorylation process, due to mutations either in the mitochondrial or nuclear genome. Among them, the mitochondrial neuro-gastrointestinal encephalo-myopathy (MNGIE) syndrome affects adolescents or young adults, and is mostly caused by TYMP mutations encoding a cytosolic thymidine phosphorylase (TP). PATIENTS AND METHODS: The present study reports the molecular investigation by next-generation re-sequencing of 281 nuclear genes, encoding mitochondrial proteins, of consanguineous family including two individuals with MNGIE syndrome associated to optic atrophy. Bioinformatic analysis was also performed in addition to mtDNA deletion screening and mtDNA copy number quantification in blood of the two patients which were carried out by solf clipping program and qPCR respectively. RESULTS: Next-generation re-sequencing revealed a novel homozygous c.2391G > T POLG mutation (p.M797I) co-occurring with the hypomorphic c.1311A > G OPA1 variant (p.I437M). Analysis of the mitochondrial genome in the two patients disclosed mtDNA depletion in blood, but no deletion. Bio-informatics investigations supported the pathogenicity of the novel POLG mutation that is located in the C-terminal subdomain and might change POLG 3D structure, stability and function. CONCLUSION: The novel homozygous p.M797I POLG mutation is responsible for MNGIE combined to optic atrophy and mtDNA depletion in the two patients.

A mitochondrial neurogastrointestinal encephalomyopathy with intestinal pseudo-obstruction resulted from a novel splice site mutation.

Mitochondrial neurogastrointestinal encephalopathy (MNGIE) is an autosomal recessive disorder characterized by gastrointestinal dysmotility, cachexia, ptosis, peripheral neuropathy and leukoencephalopathy. The diagnosis is often not made until 5-10 years after the onset of symptoms. MNGIE is caused by mutations in thymidine phosphorylase gene TYMP. Here, we present a 19-year-old boy with MNGIE who had a chronic intestinal pseudo-obstruction, and we describe his family history. Genetic analysis revealed a novel homozygous c.765+1G>C intronic mutation which is expected to disrupt splicing of TYMP in the patient. Family screening revealed that the brother was also affected and the mother was a carrier. MNGIE should be considered and genetic testing instigated if individuals with cachexia have neuromuscular complaints or symptoms of chronic intestinal pseudo-obstruction.