Late-onset oculogastrointestinal muscular dystrophy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE): Position paper on diagnosis, prognosis, and treatment by the MNGIE International Network

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive disease caused by TYMP mutations and thymidine phosphorylase (TP) deficiency. Thymidine and deoxyuridine accumulate impairing the mitochondrial DNA maintenance and integrity. Clinically, patients show severe and progressive gastrointestinal and neurological manifestations. The onset typically occurs in the second decade of life and mean age at death is 37 years. Signs and symptoms of MNGIE are heterogeneous and confirmatory diagnostic tests are not routinely performed by most laboratories, accounting for common misdiagnosis. Factors predictive of progression and appropriate tests for monitoring are still undefined. Several treatment options showed promising results in restoring the biochemical imbalance of MNGIE. The lack of controlled studies with appropriate follow-up accounts for the limited evidence informing diagnostic and therapeutic choices. The International Consensus Conference (ICC) on MNGIE, held in Bologna, Italy, on 30 March to 31 March 2019, aimed at an evidence-based consensus on diagnosis, prognosis, and treatment of MNGIE among experts, patients, caregivers and other stakeholders involved in caring the condition. The conference was conducted according to the National Institute of Health Consensus Conference methodology. A consensus development panel formulated a set of statements and proposed a research agenda. Specifically, the ICC produced recommendations on: (a) diagnostic pathway; (b) prognosis and the main predictors of disease progression; (c) efficacy and safety of treatments; and (f) research priorities on diagnosis, prognosis, and treatment. The Bologna ICC on diagnosis, management and treatment of MNGIE provided evidence-based guidance for clinicians incorporating patients' values and preferences.

Mitochondrial neurogastrointestinal encephalomyopathy: approaches to diagnosis and treatment

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare disease caused by mutations in TYMP, the gene encoding for the enzyme thymidine phosphorylase. The resulting enzyme deficiency leads to a systemic accumulation of thymidine and 2’-deoxyuridine and ultimately mitochondrial failure due to a progressive acquisition of secondary mitochondrial DNA (mtDNA) mutations and mtDNA depletion. MNGIE is characterised by gastrointestinal dysmotility, cachexia, peripheral neuropathy, ophthalmoplegia, ptosis and leukoencephalopathy. The disease is progressively degenerative and leads to death at an average age of 37.6 years. Patients invariably encounter misdiagnoses, diagnostic delays, and non-specific clinical management. Despite its rarity, MNGIE has invoked much interest in the development of therapeutic strategies, mainly because it is one of the few mitochondrial disorders where the molecular abnormality is metabolically and physically accessible to manipulation. This review provides a resume of the current diagnosis and treatment approaches and aims to increase the clinical awareness of MNGIE and thereby facilitate early diagnosis and timely access to treatments, before the development of untreatable and irreversible organ damage.

Mitochondrial Neurogastrointestinal Encephalomyopathy: Into the Fourth Decade, What We Have Learned So Far

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare metabolic autosomal recessive disease, caused by mutations in the nuclear gene TYMP which encodes the enzyme thymidine phosphorylase. The resulting enzyme deficiency leads to a systemic accumulation of the deoxyribonucleosides thymidine and deoxyuridine, and ultimately mitochondrial failure due to a progressive acquisition of secondary mitochondrial DNA (mtDNA) mutations and mtDNA depletion. Clinically, MNGIE is characterized by gastrointestinal and neurological manifestations, including cachexia, gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, ophthalmoplegia and ptosis. The disease is progressively degenerative and leads to death at an average age of 37.6 years. As with the vast majority of rare diseases, patients with MNGIE face a number of unmet needs related to diagnostic delays, a lack of approved therapies, and non-specific clinical management. We provide here a comprehensive collation of the available knowledge of MNGIE since the disease was first described 42 years ago. This review includes symptomatology, diagnostic procedures and hurdles, in vitro and in vivo disease models that have enhanced our understanding of the disease pathology, and finally experimental therapeutic approaches under development. The ultimate aim of this review is to increase clinical awareness of MNGIE, thereby reducing diagnostic delay and improving patient access to putative treatments under investigation.

Clinical Manifestations of Severe Gastrointestinal Motility Disturbance

Severe gastrointestinal motility disturbance, or pseu doobstruction, can cause symptoms and signs that mimic mechanical bowel obstruction in patients. The symptoms depend on the parts of the gastrointestinal tract involved. Patients may have dysphagia with esoph ageal involvement, gastroparesis with stomach involve ment, intestinal pseudoobstruction with small bowel in volvement, or colonic pseudoobstruction with colonic involvement. Patients often have involvement of more than one part of the gastrointestinal tract. Gastrointesti nal motility abnormality can be the result of diseases that cause either smooth muscle or myenteric plexus abnormalities and dysfunction. It is important to locate the dysfunctional segment of the bowel so that proper treatment can be initiated. The incidence of severe gas trointestinal motility disturbance is not known, but it is probably more common than has been recognized. Me chanical obstruction of the bowel is much more com mon than pseudoobstruction; therefore, it must be ruled out before a diagnosis of pseudoobstruction is made. Gastrointestinal contents are moved along the di gestive tract as a result of normal coordinated pro pulsion of its wall. Abnormal gastrointestinal motil ity from either hypoactivity or uncoordinated hyperactivity causes ineffective propulsion and re tention of the contents in the defective organ. Ob structive symptoms of the defective organ will de velop in patients with severe gastrointestinal motility disturbance. Table 1 lists these manifesta tions. They may occur individually or in combi nation, depending on the diseases that cause the abnormal motility. In this review we discuss pathophysiology, causes, clinical manifestations, diagnosis, and treatment of these problems.

Digestive smooth muscle mitochondrial myopathy in patients with mitochondrial-neuro-gastro-intestinal encephalomyopathy (MNGIE)

We report 3 new cases of Mitochondrial-Neuro-Gastro-Intestinal Encephalomyopathy (MNGIE) (or Pseudo-Obstruction-Leukoencephalopathy-Intestinal-Pseudoobstruction Syndrome [POLIP]), a rare disease that associates chronic intestinal pseudo-obstruction (CIPO) and neurological symptoms. A review of the 72 reported cases together with these 3 cases revealed that this condition was associated with (a) a specific cluster of neurological symptoms including leukoencephalopathy (96%), polyneuropathy (96%), ophthalmoplegia (91%) and hearing loss (55%); (b) a CIPO syndrome with the presence of small bowel diverticulae (53%); and (c) mitochondrial cytopathy in 36 of the 37 tested patients (2 of our 3 cases), and thymidine phosphorylase gene mutations in all the 37 tested patients (2 of our cases). The etiology of POLIP/MNGIE syndrome appears therefore to be due to a mitochondrial cytopathy secondary to thymidine phosphorylase gene mutation(s). In 3 cases, including 2 of our 3 patients, mitochondrial abnormalities were evidenced at the ultrastructural level in digestive smooth muscle demonstrating that the pathogenesis of gastrointestinal involvement was directly related to mitochondrial alterations in digestive smooth muscle cells.

Familial mitochondrial intestinal pseudo-obstruction and neurogenic bladder

Intestinal dysmotility and neurogenic bladder have been described as part of two autosomal-recessive mitochondrial disorders assumed to be due to a defect in communication between the nuclear and mitochondrial genomes: myoneurogastrointestinal encephalopathy (MNGIE) and diabetes insipidus, diabetes mellitus, optic atrophy, and deafness (Wolfram syndrome). Partial cytochrome c oxidase deficiency has been described in both. We describe three Ashkenazi Jewish siblings with progressive intestinal dysmotility, neurogenic bladder, and autonomic manifestations but no central nervous system involvement. Cytochrome c oxidase deficiency was demonstrated in peripheral and multiple intestinal muscle biopsies. Mitochondrial DNA analysis of an intestinal biopsy of patient 1 showed heteroplasmy consisting of a normal 16.5-kb band and an approximately 28-kb band, suggestive of a duplication. Mitochondrial DNA analysis of a muscle biopsy of patient 2 showed multiple deletions, mainly 10- and 11-kb bands. We suggest that this unique combination of intestinal pseudo-obstruction and neurogenic bladder could comprise a new autosomal-recessive mitochondrial disorder.

Oxidative phosphorylation disease diagnosis

Although the mtDNA encodes only 13 polypeptide subunits of the OXPHOS enzymes, approximately 1,000 proteins are estimated to be necessary for proper OXPHOS function. Over the past 10 years a wide variety of adult and pediatric OXPHOS diseases were found to be caused by or associated with mitochondrial DNA (mtDNA) mutations and nuclear DNA mutations. These advances enhanced the ability to definitively diagnose patients, develop management plans, and provide genetic counseling. Recently described nuclear DNA and mtDNA mutations are enhancing our understanding of this complex group of diseases. The impact of these advances on our understanding of OXPHOS disease pathogenesis will be reviewed.

Mitochondrial myopathy diagnosis

Oxidative phosphorylation (OXPHOS) accounts for approximately 95% of the adenosine triphosphate (ATP) produced by the cell. The central nervous system, peripheral nervous system, cardiac muscle, skeletal muscle, and smooth muscle are highly susceptible to dysfunction of this complex enzyme system. Although most OXPHOS diseases are multisystem disorders, the neuromuscular manifestations are often prominent and play an important role in patient diagnosis. To assist the neurologist in evaluating these complex patients, this article focuses on selected samples of OXPHOS diseases with identifiable neuromuscular abnormalities and presents an evaluation algorithm to facilitate patient diagnosis.

Family studies of infantile visceral myopathy: a congenital myopathic pseudo-obstruction syndrome

We conducted family studies of a rare congenital myopathic pseudo-obstruction to provide recurrence risks to families of affected children. This infantile visceral myopathy (IVM) involves the smooth muscles of the digestive tract and frequently the urinary bladder. Family and pregnancy histories from 16 families were evaluated to identify possible environmental or genetic components. The families were ethnically and geographically diverse within the United States. Eleven of the children were alive, four had died, and the status of one was unknown. The sex ratio was 5 females to 11 males. The pregnancy histories provided no evidence of a teratogenic cause. In one family, the disorder passed from parent to child. There were no consanguineous matings, no similarly affected sibs, and except for one case, the family histories did not suggest affected relatives. We suspect a new dominant mutation may be responsible for some cases of IVM, whereas in others, IVM may be caused from a dominant gene with variable expressivity and incomplete penetrance. Therefore, we predict the recurrence risk of severely affected children is much less than the 25 or 50% risk sometimes given families based on the assumption of autosomal recessive or autosomal dominant inheritance. When counseling IVM families, a thorough family history is essential. Subsequent pregnancies should be monitored by ultrasound for megacystis that was detected prenatally in seven of these cases.

A novel mitochondrial G8313A mutation associated with prominent initial gastrointestinal symptoms and progressive encephaloneuropathy

We describe a childhood mitochondrial disorder in which the clinical symptoms began and remained confined to the gastrointestinal (GI) system during the first 4 y. Seizures heralded the onset of progressive encephalopathy at age 7. Peripheral neuropathy, retinitis pigmentosa, and neural deafness developed subsequently. Laboratory investigations disclosed elevated levels of plasma lactate, and a muscle biopsy revealed ragged red fibers lacking cytochrome c oxidase activity and diminished levels of respiratory chain enzyme complexes. Molecular genetic tests failed to show any of the previously reported pathogenic mitochondrial DNA (mtDNA) mutations. We therefore screened the whole mitochondrial genome by coupling restriction digestions with single-strand conformational polymorphism (SSCP) patterns. We identified a unique SSCP in the segment that encompassed the tRNA(Lys) gene, and direct sequencing of this segment revealed a G-->A transition at an evolutionarily conserved nucleotide at mtDNA position 8313. This G8313A transition was heteroplasmic in muscle and fibroblasts of the patient, but was absent in the white blood cells and platelets from his maternal relatives. This report illustrates how GI symptoms can be the initial manifestation in a mitochondrial disorder and suggests that mitochondrial dysfunction should be considered in differentials of unexplained chronic GI symptoms, especially when lactic acidosis or other unrelated clinical signs or symptoms are present.

Impairment of central and peripheral myelin in mitochondrial diseases

Clinical or sub-clinical impairment of central and peripheral myelin is often part of the overlapping multisystem disorders associated with a variety of mitochondrial (mt)DNA abnormalities. Suboptimal energy metabolism of the oligodendrocytes and Schwann cells carrying mitochondrial defects may cause insufficient production of myelin. Further, edema, vascular and toxic factors may directly damage myelin. The recognition that certain mtDNA point mutations are associated with inflammatory demyelination of the central nervous system suggests that additional mechanisms besides degeneration need to be considered in the development of some forms of myelin damage.

Chronic intestinal pseudoobstruction with myopathy and ophthalmoplegia. A muscular biochemical study of a mitochondrial disorder

The association of chronic intestinal pseudoobstruction with ophthalmoplegia has been reported previously in visceral myopathies. We report a case of this association in which muscle mitochondria had a crystalline appearance, a dense core, and decreased cytochrome c oxidase and succinate cytochrome c reductase activities. The absence of evident mitochondrial DNA deletion in the skeletal muscle of this patient does not exclude the possibility of localized deletion or mutation of mitochondrial DNA in digestive muscle.

Familial visceral myopathy. A family with involvement of four generations

A family with the autosomal dominant form of familial visceral myopathy is described involving four generations. The members illustrate several different clinical presentations including severe constipation, diarrhea, alternating constipation and diarrhea, volvulus, urinary tract infection, and retention of urine. One patient's history suggested that the uterus may have been involved. Diagnosis of this rare disease requires an awareness of the variable presentation and a careful histological examination of full-thickness sections of bowel. The potential pitfalls in both histological and clinical diagnosis of this condition are demonstrated in this family's history. The extensive involvement of small and large bowel in at least two family members is unusual in the autosomal dominant form of the disease, but their course has so far been favorable, lending further evidence to the impression that prognosis is good. This is of importance for genetic counseling of families who have this very rare disease.

Neuromuscular disease of the gastrointestinal tract

Gastrointestinal motility is the function of gastrointestinal smooth muscle. It is controlled by both the intrinsic and extrinsic nerves of the gastrointestinal tract and, to a lesser degree, the gastrointestinal hormones. Therefore, any abnormality of the above factors, theoretically, can cause gastrointestinal dysmotility. In a clinical situation, commonly seen is gastrointestinal dysmotility caused by either smooth muscle or intrinsic and extrinsic nerves dysfunction. Diseases that cause smooth muscle dysfunction include familial visceral myopathies, nonfamilial visceral myopathies, collagen disease, muscular dystrophies, amyloidosis, thyroid disease, and so on. Diseases that cause enteric nerve dysfunction include familial visceral neuropathies, nonfamilial visceral neuropathies, diabetes mellitus, Chagas' disease, ganglioneuromatosis of the intestine, visceral neuropathy of carcinomatosis, Parkinson's disease, and so on. The patients with neuromuscular disease of the gastrointestinal tract have a wide range of clinical manifestations regardless of the underlying cause. At one end of the spectrum, the patients may be asymptomatic, and at the other end of the spectrum, the patients may have functional obstruction of the gastrointestinal tract. Plain abdominal x-rays, upper gastrointestinal (UGI) and small bowel x-rays, enteroclysis, barium enema, and manometric studies are useful for the work-up of these patients. Enteroclysis is especially helpful in ruling out mechanical obstruction of the small intestine in patients with chronic intestinal pseudo-obstruction. Treatment is mainly symptomatic and supportive. There is no effective drug to improve gastrointestinal motility. Surgery may be helpful in selected cases of severe gastrointestinal dysmotility.

Adult onset lipid storage in gastric mucosa and skeletal muscle fibers associated with gastric pain, progressive muscle weakness and partial deficiency of cytochrome C oxidase

We report on the first case, a 21-year-old man, with partial deficiency of cytochrome c oxidase, lipid storage myopathy and concomitant lipid storage in the gastric mucosa affecting chief, parietal, and argentaffine cells as well as interstitial macrophages. The clinical symptoms consisted of increasing muscle weakness, cramps of the legs, and severe gastric pain that was resistant to treatment. Muscle biopsy specimens showed severe lipid storage in muscle fibers. Enzyme histochemistry revealed partial deficiency of cytochrome c oxidase (COX) with scattered non-reactive fibers among a majority of COX-positive fibers whereas biochemical analysis of muscle homogenates resulted in no corresponding defect of mitochondrial enzymes. Gastric biopsy specimens showed similarly to muscle fibers an extensive accumulation of lipid droplets in the chief cells, HCl producing parietal cells, macrophages, neutrophilic and eosinophilic leucocytes, and to a lesser degree also in argentaffine cells and unmyelinated axons of the gastric mucosa. The lipid droplets were associated with an insignificant increase in the number and size of mitochondria although paracristalline mitochondrial inclusions were neither noted in muscle fibers nor in cells of the gastric mucosa. These findings resemble those in multisystem triglyceride storage disease although the clinical signs were not reminiscent of this disease, and indicate that among the clinically heterogeneous group of cytochrome c oxidase deficiencies lipid storage may not be confined to muscle, but can affect the gastric mucosa as well.

Polyneuropathy, ophthalmoplegia, leukoencephalopathy, and intestinal pseudo-obstruction: POLIP syndrome

We describe 5 individuals (from three separate families) with a progressive neurological disorder characterized by sensorimotor peripheral polyneuropathy, cranial neuropathies (external ophthalmoplegia, deafness), and the syndrome of chronic intestinal pseudo-obstruction. Magnetic resonance imaging showed widespread abnormality of the cerebral and cerebellar white matter in the 2 patients studied. Autopsy examination in 3 revealed widespread endoneurial fibrosis and demyelination in the peripheral nervous system, possibly secondary to axonal atrophy, and poorly defined changes in cerebral white matter (leukoencephalopathy). The cranial nerves and spinal roots were less severely involved and the neurons in the brainstem and spinal cord were intact. The fatal gastrointestinal dysmotility was due to a severe visceral neuropathy. We suggest that these patients manifested a hereditary disorder with distinctive clinical, radiological, and neuropathological features, and propose the acronym POLIP to emphasize the distinctive tetrad of polyneuropathy, ophthalmoplegia, leukoencephalopathy, and intestinal pseudo-obstruction.

Disorders of gastrointestinal motility in neurologic diseases

Neurologic diseases can affect the bowel at several levels of innervation--by altering the electrical activity that controls smooth muscle, the enteric nervous system, or the extrinsic neural pathways to the gut. This review concentrates on disorders of motility that occur in conjunction with diseases of the extrinsic neural supply (from the level of the brain to the postganglionic fibers) and those generalized disorders that affect gut smooth muscle. Modern technology, such as gastrointestinal scintigraphy and manometric techniques that measure esophageal, gastroduodenal, and anorectal motility (intraluminal pressures), has provided better methods to study the pathophysiologic aspects of gut motility in diseases of the nervous system. Distinguishing the neuropathies of the extrinsic nervous system from those of the intrinsic (enteric) nervous system is not always possible because the available techniques evaluate only the end-organ--that is, the motor function of the gut. Degenerative or infiltrative (myopathic) disorders of gut smooth muscle, however, can be distinguished from such neuropathies, and careful and systematic evaluation of autonomic function can often identify the level of disordered function in the neural-gut axis.

Familial visceral myopathy: a family with at least six involved members

A family with at least six members affected by hollow organ visceral myopathy is described. Patients in the first or second decades of life developed symptoms which included weight loss, nausea and vomiting, abdominal pain and distension, constipation and diarrhoea, and urinary symptoms. The radiological features of the disease consisted of oesophageal aperistalsis, megaduodenum, and variable dilatation of the small and large bowel. Four patients had urinary tract involvement with dilatation of the ureters and/or incomplete bladder emptying. Two patients were severely affected and needed home parenteral nutrition and surgical treatment; others were symptomatic but remained well. The characteristic pathological abnormality was vacuolar degeneration predominantly affecting the longitudinal muscle. The disease in this family appears to be transmitted by autosomal dominant mode of inheritance.

Familial autonomic visceral myopathy with degeneration of muscularis mucosae

An extended family with chronic intestinal pseudo-obstruction which affected 11 of 54 members was studied. Patients presented with recurrent intestinal obstruction in childhood or adolescence: eight of the 11 died before the age of 30. Pedigree analysis showed four consanguineous marriages. The patients were all in the fifth generation and had established an autosomal recessive mode of inheritance. Histological, immunocytochemical, and electron microscopic studies were performed on a colectomy specimen from a surviving affected family member. Familial visceral myopathy was diagnosed--characterised by degeneration and collagenous replacement of both layers of the muscularis propria and the muscularis mucosae.

Pathology of neuromuscular disorders of the small intestine and colon

A variety of pathological abnormalities of the smooth muscle and myenteric plexus result in clinical syndromes of disordered small intestinal and colonic motility. These pathological abnormalities have been noted by conventional light microscopy and by utilization of Smith's technique for visualizing the myenteric plexus with silver. We have classified the neuromuscular disorders into two major categories, i.e., those affecting the myenteric plexus and those affecting the smooth muscle. The classification is further developed based on the variety of clinicopathological features of the various disorders. Although we can now identify the underlying pathology of these motor disorders and thus understand these illnesses better than we did a decade ago, we have much more to learn. With the great strides being made to understand the normal structure, function, and development of the myenteric plexus and smooth muscle, there is hope that we will be able to learn much more about the etiology and pathogenesis of these neuromuscular disorders in the decade to come.

Myo-, neuro-, gastrointestinal encephalopathy (MNGIE syndrome) due to partial deficiency of cytochrome-c-oxidase. A new mitochondrial multisystem disorder

A 42-year-old woman had a 10-year history of external ophthalmoplegia, malabsorption resulting in chronic malnutrition, muscle atrophy and polyneuropathy. Computer tomography revealed hypodensity of her cerebral white matter. A metabolic disturbance consisted of lactic acidosis after moderate glucose loads with increased excretion of hydroxybutyric and fumaric acids. Post-mortem studies revealed gastrointestinal scleroderma as the morphological manifestation of her malabsorption syndrome, ocular and skeletal myopathy with ragged red fibers, peripheral neuropathy, vascular abnormalities of meningeal and peripheral nerve vessels. Biochemical examination of the liver and muscle tissues revealed a partial defect of cytochrome-c-oxidase (complex IV of the respiratory chain). This mitochondrial multisystem disorder may represent a separate entity to be classified between the spectrum of myoencephalopathies and oculo-gastrointestinal muscular dystrophy.

A familial visceral myopathy with dilatation of the entire gastrointestinal tract

We are reporting a new kindred in which familial visceral myopathy was identified in four siblings. There was no other symptomatic case identified in this 75-member, four-generation family, suggesting an autosomal recessive inheritance. All patients had recurrent symptoms of intestinal obstruction, and 3 died from malnutrition. Gastrointestinal lesions showed marked dilatation of the entire digestive tract from the esophagus to the rectum, which is different from other types of familial visceral myopathies. Microscopic examination of the gastrointestinal smooth muscle showed degeneration and increased fibrosis indistinguishable from other types of familial visceral myopathy.