The human mitochondrial genome is replicated by DNA polymerase γ, which is encoded by polymerase γ gene (POLG1) on chromosome 15q25. Patients with POLG1 mutations usually present as Alpers’ syndrome or progressive external ophthalmoplegia. Our patient was a 48-year old woman with sensory ataxic neuropathy, dysarthria, ophthalmoplegia, and dysphagia. Sequence analysis revealed that she has two heterozygous missense mutations in the POLG1, a c.1774C>T substitution in exon 10, which results in a p.L591F amino acid change; and a c.3286C>T substitution in exon 21, which results in a p.R1096C amino acid change. The 1774C>T substitution is a novel mutation.
Previously described adult patients with one mutation in exon 10 and the other in exon 21 of POLG1 had presented with progressive external ophthalmoplegia. We now describe a patient with mutations in the same exons but suffering from the more complex clinical syndrome of sensory ataxic neuropathy, dysarthria, ophthalmoplegia.
Novel mutation; PEO; POLG1; SANDO
Disorders of oxidative phosphorylation affects 1/5000 individuals and present heterogeneous involvement of tissues highly dependent upon ATP production.
Here we present the case of a 48-year-old woman carrying a homozygous mutation (p.A899T) in mitochondrial polymerase gamma (POLG) and manifesting with a complex neurological phenotype including Dopamine-agonist responsive Parkinsonism.
This case report is further evidence that mitochondrial dysfunction might play a role in Parkinson’s Disease pathogenesis and helps in identification of apparent mutation-specific clinical characteristics. Mutations in POLG should be looked for in cases of Parkinsonism, especially when multisystem neurological involvement is found.
POLG; Parkinsonism; Mitochondrial dysfunction; Ataxia; Progressive external ophthalmoparesis
Autosomal dominant Progressive External Ophthalmoplegias are Mendelian disorders characterized by the accumulation of multiple deletions of mitochondrial DNA in critical tissues. Most of the Autosomal dominant Progressive External Ophthalmoplegias families carry heterozygous mutations in one of three genes: ANT1, encoding the muscle-heart specific mitochondrial adenine nucleotide translocator, Twinkle, encoding the mitochondrial DNA helicase, and POLG1, encoding the catalytic subunit of the mitochondrial DNA-specific polymerase. Mutations in both POLG1 alleles are also found in autosomal recessive Progressive External Ophthalmoplegias sibships with multiple affected members and in apparently sporadic cases. In addition, recessive POLG1 mutations are responsible for three additional diseases: Alpers-Huttenlocher hepatopathic poliodystrophy, Sensory-Ataxic Neuropathy Dysarthria and Ophthalmoplegia and juvenile SpinoCerebellar Ataxia-Epilepsy syndrome. Mitochondrial neuro-gastro-intestinal encephalomyopathy is an autosomal recessive disorder of juvenile onset, caused by mutations in the gene encoding Thymidine Phosphorylase. Thymidine Phosphorylase is involved in the control and maintenance of the pyrimidine nucleoside pool of the cell. Finally, mitochondrial DNA depletion syndrome is a heterogeneous group of disorders characterized by a reduction in mitochondrial DNA copy number. Clinically, they include a myopathic form, a more generalized encephalomyopathic form and a fatal infantile hepato-cerebral syndrome leading to rapidly progressive liver and brain failure. To date, eight genes have been associated with mitochondrial DNA depletion syndrome. Novel disease genes have recently been added to this list, including OPA1 and GFER, and new clinical variants add further complexity to this expanding area of mitochondrial medicine.
Mitochondrial DNA; oxidative phosphorylation; mitochondrial disorders; MtDNA multiple deletions; MtDNA depletion
Polymerase-γ (POLG) is a major human disease gene and may account for up to 25% of all mitochondrial diseases in the UK and in Italy. To date, >150 different pathogenic mutations have been described in POLG. Some mutations behave as both dominant and recessive alleles, but an autosomal recessive inheritance pattern is much more common. The most frequently detected pathogenic POLG mutation in the Caucasian population is c.1399G>A leading to a p.Ala467Thr missense mutation in the linker domain of the protein. Although many patients are homozygous for this mutation, clinical presentation is highly variable, ranging from childhood-onset Alpers-Huttenlocher syndrome to adult-onset sensory ataxic neuropathy dysarthria and ophthalmoparesis. The reasons for this are not clear, but familial clustering of phenotypes suggests that modifying factors may influence the clinical manifestation. In this study, we collected clinical, histological and biochemical data from 68 patients carrying the homozygous p.Ala467Thr mutation from eight diagnostic centres in Europe and the USA. We performed DNA analysis in 44 of these patients to search for a genetic modifier within POLG and flanking regions potentially involved in the regulation of gene expression, and extended our analysis to other genes affecting mitochondrial DNA maintenance (POLG2, PEO1 and ANT1). The clinical presentation included almost the entire phenotypic spectrum of all known POLG mutations. Interestingly, the clinical presentation was similar in siblings, implying a genetic basis for the phenotypic variability amongst homozygotes. However, the p.Ala467Thr allele was present on a shared haplotype in each affected individual, and there was no correlation between the clinical presentation and genetic variants in any of the analysed nuclear genes. Patients with mitochondrial DNA haplogroup U developed epilepsy significantly less frequently than patients with any other mitochondrial DNA haplotype. Epilepsy was reported significantly more frequently in females than in males, and also showed an association with one of the chromosomal markers defining the POLG haplotype. In conclusion, our clinical results show that the homozygous p.Ala467Thr POLG mutation does not cause discrete phenotypes, as previously suggested, but rather there is a continuum of clinical symptoms. Our results suggest that the mitochondrial DNA background plays an important role in modifying the disease phenotype but nuclear modifiers, epigenetic and environmental factors may also influence the severity of disease.
mitochondrial diseases; neuromuscular disorders; genetics; phenotype; molecular biology
Mitochondrial neurogastrointestinal encephalomyopathy is a rare multisystemic autosomic recessive disorder characterized by: onset typically before the age of 30 years; ptosis; progressive external ophthalmoplegia; gastrointestinal dysmotility; cachexia; peripheral neuropathy; and leucoencephalopathy. The disease is caused by mutations in the TYMP gene encoding thymidine phosphorylasethymine phosphorylase. Anecdotal reports suggest that allogeneic haematopoetic stem cell transplantation may be beneficial for mitochondrial neurogastrointestinal encephalomyopathy, but is associated with a high mortality. After selecting patients who fulfilled the clinical criteria for mitochondrial neurogastrointestinal encephalomyopathy and had severe thymidine phosphorylase deficiency in the buffy coat (<10% of normal activity), we reviewed their medical records and laboratory studies. We identified 102 patients (50 females) with mitochondrial neurogastrointestinal encephalomyopathy and an average age of 32.4 years (range 11–59 years). We found 20 novel TYMP mutations. The average age-at-onset was 17.9 years (range 5 months to 35 years); however, the majority of patients reported the first symptoms before the age of 12 years. The patient distribution suggests a relatively high prevalence in Europeans, while the mutation distribution suggests founder effects for a few mutations, such as c.866A>G in Europe and c.518T>G in the Dominican Republic, that could guide genetic screening in each location. Although the sequence of clinical manifestations in the disease varied, half of the patients initially had gastrointestinal symptoms. We confirmed anecdotal reports of intra- and inter-familial clinical variability and absence of genotype–phenotype correlation in the disease, suggesting genetic modifiers, environmental factors or both contribute to disease manifestations. Acute medical events such as infections often provoked worsening of symptoms, suggesting that careful monitoring and early treatment of intercurrent illnesses may be beneficial. We observed endocrine/exocrine pancreatic insufficiency, which had not previously been reported. Kaplan–Meier analysis revealed significant mortality between the ages of 20 and 40 years due to infectious or metabolic complications. Despite increasing awareness of this illness, a high proportion of patients had been misdiagnosed. Early and accurate diagnosis of mitochondrial neurogastrointestinal encephalomyopathy, together with timely treatment of acute intercurrent illnesses, may retard disease progression and increase the number of patients eligible for allogeneic haematopoetic stem cell transplantation.
mitochondrial disease; MNGIE; encephalomyopathy; TYMP; BMT
Mitochondrial genetic diseases can result from defects in mitochondrial DNA (mtDNA) in the form of deletions, point mutations, or depletion, which ultimately cause loss of oxidative phosphorylation. These mutations may be spontaneous, maternally inherited, or a result of inherited nuclear defects in genes that maintain mtDNA. This review focuses on our current understanding of nuclear gene mutations that produce mtDNA alterations and cause mitochondrial depletion syndrome (MDS), progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). To date, all of these etiologic nuclear genes fall into one of two categories: genes whose products function directly at the mtDNA replication fork, such as POLG, POLG2, and TWINKLE, or genes whose products supply the mitochondria with deoxynucleotide triphosphate pools needed for DNA replication, such as TK2, DGUOK, TP, SUCLA2, ANT1, and possibly the newly identified MPV17.
DNA polymerase γ; nucleotide pools; mitochondrial DNA depletion syndrome; progressive external ophthalmoplegia; ataxia-neuropathy
Mutations in the POLG gene have emerged as one of the most common causes of inherited mitochondrial disease in children and adults. They are responsible for a heterogeneous group of at least 6 major phenotypes of neurodegenerative disease that include: 1) childhood Myocerebrohepatopathy Spectrum disorders (MCHS), 2) Alpers syndrome, 3) Ataxia Neuropathy Spectrum (ANS) disorders, 4) Myoclonus Epilepsy Myopathy Sensory Ataxia (MEMSA), 5) autosomal recessive Progressive External Ophthalmoplegia (arPEO), and 6) autosomal dominant Progressive External Ophthalmoplegia (adPEO). Due to the clinical heterogeneity, time-dependent evolution of symptoms, overlapping phenotypes, and inconsistencies in muscle pathology findings, definitive diagnosis relies on the molecular finding of deleterious mutations. We sequenced the exons and flanking intron region from approximately 350 patients displaying a phenotype consistent with POLG related mitochondrial disease and found informative mutations in 61 (17%). Two mutant alleles were identified in 31 unrelated index patients with autosomal recessive POLG-related disorders. Among them, 20 (67%) had Alpers syndrome, 4 (13%) had arPEO, and 3 (10%) had ANS. In addition, 30 patients carrying one altered POLG allele were found. A total of 25 novel alterations were identified, including 6 null mutations. We describe the predicted structural/functional and clinical importance of the previously unreported missense variants and discuss their likelihood of being pathogenic. In conclusion, sequence analysis allows the identification of mutations responsible for POLG-related disorders and, in most of the autosomal recessive cases where two mutant alleles are found in trans, finding deleterious mutations can provide an unequivocal diagnosis of the disease.
POLG; POLG1; Alpers syndrome; PEO; adPEO; arPEO; SANDO; SCAE; ANS; MEMSA; MCHS; mtDNA depletion; liver failure
Introduction. Pantothenate-kinase-associated neurodegeneration (PKAN) is a rare genetic disease and a form of neurodegeneration with brain iron accumulation (NBIA). It most commonly begins in the first two decades of life but should be considered in the differential diagnosis of patients at any age with an atypical progressive extrapyramidal disorder and cognitive impairment. Few late-adult cases have been reported. Case Report. A 50-year-old woman presented with a history of progressive dysarthria and dysphagia secondary to orolingual dystonia. Initial work-up was normal. There was no family history. Her initial symptoms were followed by the onset of blepharospasm, cervical dystonia, Parkinsonism, and cognitive impairment. Follow-up MRI four years after presentation revealed the diagnostic “eye-of-the-tiger” sign. Genetic testing confirmed a homozygous missense mutation consistent with the diagnosis of PKAN. Conclusion. Although PKAN is a rare genetic disorder most commonly seen in childhood, it should be considered in adult patients with a history of progressive focal dystonia or atypical Parkinsonism. As the radiographic findings are quite characteristic, genetic testing should be performed if the MRI shows evidence of iron accumulation. Optimal treatment strategies are not known, and at the current time therapies should be directed at the specific manifestations of the disease.
DNA polymerase γ (pol γ), encoded by POLG, is responsible for replicating human mitochondrial DNA. About 150 mutations in the human POLG have been identified in patients with mitochondrial diseases such as Alpers syndrome, progressive external ophthalmoplegia, and ataxia-neuropathy syndromes. Because many of the mutations are described in single citations with no genotypic family history, it is important to ascertain which mutations cause or contribute to mitochondrial disease. The vast majority of data about POLG mutations has been generated from biochemical characterizations of recombinant pol γ. However, recently, the study of mitochondrial dysfunction in Saccharomyces cerevisiae and mouse models provides important in vivo evidence for the role of POLG mutations in disease. Also, the published 3D-structure of the human pol γ assists in explaining some of the biochemical and genetic properties of the mutants. This review summarizes the current evidence that identifies and explains disease-causing POLG mutations.
Mitochondria; mtDNA replication; DNA polymerase gamma; POLG; DNA repair
Mutations in the gene encoding the catalytic subunit of polymerase γ (POLG1) are a major cause of human mitochondrial disease. More than 150 different point mutations in the gene have been reported to be disease causing, resulting in a large range of clinical symptoms. Depending on the mutation or combination of mutations, disease onset can occur in early infancy or late in adult life. Here, we describe the use of multiplex ligation-dependent probe amplification (MLPA) analysis to detect deletions within POLG1, which could otherwise go undetected by solely sequencing of the gene. We present a case where an entire POLG1 allele is deleted, with a known pathogenic mutation (W748S) on the remaining allele. The deletion was found in a boy with Alpers syndrome, presenting at 18 months of age with slightly retarded motor development, balance problems, and seizures. Administration of valproic acid (VPA) led to rapidly progressive fatal liver failure in our patient, and we would like to highlight the need to carry out complete POLG1 gene analysis before administration of VPA in cases of pediatric seizure disorders of unknown origin. Debut and severity of the disease in this patient was unique when compared to homozygous or heterozygous patients with the W748S mutation, leading to the conclusion that gene dosage plays a role in the clinical phenotype of this disease.
Bulbar weakness and fatigue resulting in dysphagia and dysarthria is common in myasthenia gravis. In chronic MG it is often assumed that these symptoms herald an exacerbation of the patient's disease and doses of cholinergic agents and immunomodulatory therapies may be increased, along with initiation of plasma exchange. A case is presented in which dysphagia was refractory to standard MG therapy, leading to the subsequent discovery of cricopharyngeal sphincter achalasia as the primary cause of the patient's symptoms rather than an assumed myasthenia gravis exacerbation. The patient's dysphagia resolved after esophageal dilatation. Cricopharyngeal sphincter achalasia is a common disorder producing dysphagia in the elderly and needs to be considered in the evaluation of a myasthenic patient with worsening dysphagia when standard myasthenia gravis therapy fails. Discussion of myasthenia gravis, cholinergic therapy and cricopharyngeal sphincter achalasia is undertaken. Clinicians are encouraged to consider non-neurologic causes of worsening dysphagia in the myasthenic patient.
Mitochondrial DNA (mtDNA) is replicated by the DNA polymerase γ in concert with accessory proteins such as the mitochondrial DNA helicase, single stranded DNA binding protein, topoisomerase, and initiating factors. Nucleotide precursors for mtDNA replication arise from the mitochondrial salvage pathway originating from transport of nucleosides, or alternatively from cytoplasmic reduction of ribonucleotides. Defects in mtDNA replication or nucleotide metabolism can cause mitochondrial genetic diseases due to mtDNA deletions, point mutations, or depletion which ultimately cause loss of oxidative phosphorylation. These genetic diseases include mtDNA depletion syndromes (MDS) such as Alpers or early infantile hepatocerebral syndromes, and mtDNA deletion disorders, such as progressive external ophthalmoplegia (PEO), ataxia-neuropathy, or mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). This review focuses on our current knowledge of genetic defects of mtDNA replication (POLG, POLG2, C10orf2) and nucleotide metabolism (TYMP, TK2, DGOUK, and RRM2B) that cause instability of mtDNA and mitochondrial disease.
DNA polymerase γ; mitochondrial DNA replication; nucleotide pools; mitochondrial DNA depletion syndrome; progressive external ophthalmoplegia; ataxia-neuropathy
POLG1 mutations have been associated with MELAS-like phenotypes. However given several clinical differences it is unknown whether POLG1 mutations are possible causes of MELAS or give raise to a distinct clinical and genetic entity, named POLG1-associated encephalopathy.
We describe a 74 years old man carrying POLG1 mutations presenting with strokes, myopathy and ragged red fibers with some atypical aspects for MELAS such as late onset, lack of cerebral calcification and presence of frontal and occipital MRI lesions better consistent with the POLG associated-encephalopathy spectrum.
The lack of available data hampers a definite diagnosis in our patient as well as makes it difficult to compare MELAS, which is a clearly defined clinical syndrome, with POLG1-associated encephalopathy, which is so far a purely molecularly defined syndrome with a quite heterogeneous clinical picture. However, the present report contributes to expand the phenotypic spectrum of POLG1 mutations underlining the importance of searching POLG1 mutations in patients with mitochondrial signs and MELAS like phenotypes but negative for common mtDNA mutations.
POLG1; MELAS; Red-ragged fibers; Stroke-like
Chronic intestinal pseudo-obstruction (CIPO) is a syndrome characterized by recurrent clinical episodes of intestinal obstruction in the absence of any mechanical cause occluding the gut. There are multiple causes related to this rare syndrome. Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is one of the causes related to primary CIPO. MNGIE is caused by mutations in the gene encoding thymidine phosphorylase. These mutations lead to an accumulation of thymidine and deoxyuridine in blood and tissues of these patients. Toxic levels of these nucleosides induce mitochondrial DNA abnormalities leading to an abnormal intestinal motility.
Herein, we described two rare cases of MNGIE syndrome associated with CIPO, which needed surgical treatment for gastrointestinal complications. In one patient, intra-abdominal hypertension and compartment syndrome generated as a result of the colonic distension forced to perform emergency surgery. In the other patient, a perforated duodenal diverticulum was the cause that forced to perform surgery. There is not a definitive treatment for MNGIE syndrome and survival does not exceed 40 years of age. Surgery only should be considered in some selected patients.
DNA polymerase γ (pol γ) is responsible for replication and repair of mitochondrial DNA (mtDNA). Over 150 mutations in POLG (which encodes pol γ) have been discovered in patients with mitochondrial disorders including Alpers, progressive external ophthalmoplegia and ataxia-neuropathy syndrome. However, the severity and dominance of many POLG disease-associated mutations are unclear, because they have been reported in sporadic cases. To understand the consequences of pol γ disease-associated mutations in vivo, we identified dominant and recessive changes in mtDNA mutagenesis, depletion and mitochondrial dysfunction caused by 31 mutations in the conserved regions of the gene, MIP1, which encodes the Saccharomyces cerevisiae ortholog of human pol γ. Twenty mip1 mutant enzymes were shown to disrupt mtDNA replication and may be sufficient to cause disease. Previously uncharacterized sporadic mutations, Q308H, R807C, G1076V, R1096H and S1104C, caused decreased polymerase activity leading to mtDNA depletion and mitochondrial dysfunction. We present evidence showing a limited role of point mutagenesis by these POLG mutations in mitochondrial dysfunction and disease progression. Instead, most mitochondrial defective mip1 mutants displayed reduced or depleted mtDNA. We also determined that the severity of the phenotype of the mip1 mutant strain correlates with the age of onset of disease associated with the human ortholog. Finally, we demonstrated that increasing nucleotide pools by overexpression of ribonucleotide reductase (RNR1) suppressed mtDNA replication defects caused by several dominant mip1 mutations, and the orthologous human mutations revealed severe nucleotide binding defects.
A woman from Italy presented with dystonic leg symptoms at the age of 59. Rapid-onset dystonia-parkinsonism (RDP) was not suspected until 3 affected children (2 male, 1 female) with presentations consistent with the disorder were recognized.
The mother and four of her children (3 with and 1 without dystonia) were evaluated with an extensive battery including standardized history questionnaire and rating scales. In addition, all four children had cognitive testing and three of the four children had psychiatric interviews.
In this family, a T613M mutation in the ATP1A3 gene was confirmed, the most common mutation present in patients with RDP. The proband's limb dystonia was atypical of RDP, symptoms of the others affected included dysarthria, asymmetric limb dystonia, and dysphagia more consistent with RDP. The two sons developed dystonia-parkinsonism in adolescence after consuming large amounts of alcohol. All 3 of those with psychiatric interviews reached diagnosable thresholds for mood disorder (bipolar or dysthymia) and some form of anxiety disorder.
The phenotype and age of onset is broader than previously reported in RDP, suggesting that it could be under-reported. Prior to this study, neuropsychologic symptoms associated with RDP were under-appreciated. Those patients who are at risk or suspected of having RDP should be cautioned to avoid excessive alcohol intake. Further study is needed to assess if the cognitive and psychiatric features are part of a broader RDP phenotype and this may have implications for future research into genetic susceptibility for psychiatric disease.
Dystonia; RDP; DYT-12; Rapid-onset dystonia-parkinsonism
Mitochondrial neurogastrointestinal encephalopathy (MNGIE) is an autosomal recessive mitochondriopathy caused by loss-of-function mutations in the thymidine phosphorylase gene. The disease leads to premature death and is characterized by gastrointestinal dysmotility and cachexia, external ophthalmoplegia, a sensorimotor neuropathy, and leukoencephalopathy. Bone marrow transplantation (BMT) is the only potentially curative treatment that can achieve a sustained biochemical correction of the metabolic imbalances.
We report a 23-year-old male homozygous for the c.866A > C, p.Glu289Ala mutation of the TYMP gene, who presented with fatty liver and cachexia. Laboratory examinations were unremarkable except for increased transaminase activities. Grade II fibrosis and steatosis was found in an initial and a follow-up liver biopsy 4 years later. Myeloablative conditioning and BMT was performed 10 years after initial presentation due to the progressive weight loss and polyneuropathy. Pre-transplant liver staging was normal except for an elevated transient elastography of 31.6 kPa. Severe ascites developed after transplantation and liver function deteriorated progressively to liver failure. Despite engraftment on day +15, the patient died on day +18 from liver failure. Autopsy revealed micronodular liver cirrhosis, and postmortem diagnosis of acute-on-chronic liver failure was done.
This case illustrates the difficulties and importance of diagnosing liver cirrhosis in MNGIE. Before BMT, patients must be carefully evaluated by transient elastography, liver biopsy, or assessment of hepatic venous pressure gradient. In patients with liver cirrhosis, further studies should evaluate if liver transplantation may be an alternative to BMT. Considerable amounts of thymidine phosphorylase are expressed in liver tissue which may prevent accumulation of toxic metabolites.
To describe a novel POLG missense mutation (c.3218C>T; p.P1073L) that, in association with 2 previously described mutations, caused an Alpers-like hepatocerebral syndrome in 4 children.
Tertiary care universities.
Four children, 2 related and 2 unrelated, with the novel p.P1073L mutation (all patients) and either the p.A467T (2 patients), p.G848S (1 patient), or p.W748S (1 patient) mutation presented with psychomotor delay, encephalopathy, and liver failure.
Detailed clinical and laboratory examinations including brain magnetic resonance imaging, muscle biopsy, measurement of mitochondrial DNA, and sequencing of the POLG gene.
Main Outcome Measures
Definition of clinical variability.
All 4 patients had psychomotor delay, seizures, and liver disease. Three patients had severe gastrointestinal dysmotility, which may be associated with the new p.P1073L mutation.
The heterozygous presence of the novel p.P1073L mutation in trans with another recessive POLG mutation causes a hepatocerebral disorder identical or very similar to Alpers syndrome. This adds to the already striking clinical heterogeneity of POLG mutations. In the Belgian patients, the familial occurrence without consanguinity is related to the high frequency of the recessive p.A467T and p.W748S mutations in northwestern Europe and reveals a pitfall for diagnosis and genetic counseling.
Decreased tongue strength (TS) might herald bulbar involvement in patients with amyotrophic lateral sclerosis (ALS) well before dysarthria or dysphagia occur, and as such might be prognostic of short survival. The purpose of this study was to investigate the prognostic value of a decreased TS, in addition to other prognostic factors, such as site of onset, bulbar symptoms, bulbar signs, age, sex, maximum phonation time, time from symptoms to diagnosis, and gastrostomy, for survival time in patients with ALS. TS was measured in four directions in 111 patients who attended the diagnostic outpatient motor neuron clinic of our university hospital. Of these patients, 54 were diagnosed with ALS. TS was considered abnormal if the strength in minimally one direction was at least two standard deviations below the reference values obtained from comparable age category and sex-groups of healthy controls (n = 119). Twenty of the patients with ALS had a decreased TS. Multivariable analysis showed that, in addition to age, TS was an independent prognostic factor for survival time in patients with ALS.
ALS; Tongue strength; Survival; Prognosis
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease due to ECGF1 gene mutations causing thymidine phosphorylase (TP) deficiency. Analysis of post-mortem samples of five MNGIE patients and two controls, revealed TP activity in all control tissues, but not in MNGIE samples. Converse to TP activity, thymidine and deoxyuridine were absent in control samples, but present in all tissues of MNGIE patients. Concentrations of both nucleosides in the tissues were generally higher than those observed in plasma of MNGIE patients. Our observations indicate that in the absence of TP activity, tissues accumulate nucleosides, which are excreted into plasma.
Mitochondria; MNGIE; thymidine phosphorylase; thymidine; deoxyuridine
Mutations in the POLG1 gene have variable phenotypic presentations and a high degree of clinical suspicion is necessary for their recognition. Parkinsonism and ataxia are the most common movement disorders associated with POLG1 mutations but no phenotype-genotype correlation has been established.
We identified a male patient with progressive external ophthalmoplegia who also developed a progressive bradykinesia, rigidity and camptocormia in the third decade. Parkinsonism was partially responsive to dopaminegic replacement. His father and brother had reportedly similar clinical problems. Genetic analysis identified a novel mutation p.K512M in the POLG1 gene.
This report further expands the spectrum of POLG1-associated neurologic problems with the report of a novel mutation in the linker region of the gene, which are rarely associated with parkinsonism.
Mitochondrial DNA polymerase gamma (POLG1); Parkinsonism; Progressive external ophthalmoplegia; Ataxia; Sensory neuropathy
Mutations in POLG1 are an important cause of human mitochondrial disease. We describe a woman who presented with bilateral ptosis and external ophthalmoplegia at 64 years of age. Neurological examination revealed symptoms of diffuse encephalopathy. The symptoms were progressive and at 67 years she was severely cognitively impaired, had severe bilateral ptosis and complete external ophthalmoplegia. Frequent cytochrome c oxidase-negative fibres were detected in muscle. Electrophysiological examination revealed myopathic changes and axonal neuropathy. Standard laboratory tests were normal. Brain CT showed general, moderate cortical atrophy. Molecular analysis of muscle DNA revealed multiple mitochondrial DNA deletions. Sequencing of the entire POLG1 gene revealed two changes c.2993C>T (p.998S>L) and c.3550G>C (p.1184D>H). Both mutations are previously unreported and confirmed to be compound heterozygous. Late-onset progressive external ophthalmoplegia with severe encephalopathy is an unusual combination in patients with POLG1 mutations. POLG-associated disease should be considered in any patient with unexplained or unusual neurological features.
The c.1550 g→t mutation in the POLG gene causing the G517V substitution has been reported by many groups to be associated with a variety of mitochondrial diseases, including autosomal dominant and recessive forms of ataxia neuropathy, myopathy and microcephaly, progressive external ophthalmoplegia, diabetes, strokes, hypotonia, and epilepsy. However, the variable disease presentation and age of onset raises suspicion of its pathogenicity. Because of the varied reported associated symptoms and request from physicians to address the consequence of this mutation, we have carried out the biochemical analysis of the purified recombinant human DNA polymerase γ protein harboring the G517V substitution. These analyses revealed that the G517V mutant enzyme retained 80-90% of wild-type DNA polymerase activity, in addition to its functional interaction with the p55 accessory subunit. DNA binding by the mutant was also only slightly lower than the wild-type enzyme. Our data suggest that the G517V mutation by itself in pol γ most likely does not have a role in mitochondrial disorders.
Deficiency of the cytosolic enzyme thymidine phosphorylase (TP) causes a multisystem disorder called mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome. Clinical symptoms are gastrointestinal dysfunction, muscle involvement and neurological deterioration. TP deficiency is biochemically characterised by accumulation of thymidine and deoxyuridine in body fluids and compromised mitochondrial deoxyribose nucleic acid (mtDNA) integrity (depletion and multiple deletions). In this report we describe a patient with the clinical and biochemical features related to the end stage of the disease. Home parenteral nutrition had started to improve the clinical condition and preparations were initiated for stem cell transplantation (SCT) as a last resort treatment. Unfortunately, the patient died during the induction phase of SCT. This report shows that TP deficiency is a severe clinical condition with a broad spectrum of affected tissues. TP deficiency can be easily determined by the measurement of pyrimidine metabolites in body fluids and TP activity in peripheral blood leucocytes. Early detection and treatment may prevent the progress of the clinical symptoms and, therefore, should be considered for inclusion in newborn screening programmes.
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a devastating autosomal recessive disorder due to mutations in TYMP, which cause loss of function of thymidine phosphorylase (TP), nucleoside accumulation in plasma and tissues and mitochondrial dysfunction. The clinical picture includes progressive gastrointestinal dysmotility, cachexia, ptosis and ophthalmoparesis, peripheral neuropathy and diffuse leukoencephalopathy, which usually lead to death in early adulthood. Therapeutic options are currently available in clinical practice (allogeneic hematopoietic stem cell transplantation and carrier erythrocyte entrapped TP therapy) and newer, promising therapies are expected in the near future. However, successful treatment is strictly related to early diagnosis. We report on an incomplete MNGIE phenotype in a young man harboring the novel heterozygote c.199 C>T (Q67X) mutation in exon 2, and the previously reported c.866 A>C (E289A) mutation in exon 7 in TYMP. The correct diagnosis was achieved many years after the onset of symptoms and unfortunately, the patient died soon after diagnosis because of multiorgan failure due to severe malnutrition and cachexia before any therapeutic option could be tried. To date, early diagnosis is essential to ensure that patients have the opportunity to be treated. MNGIE should be suspected in all patients who present with both gastrointestinal and nervous system involvement, even if the classical complete phenotype is lacking.
Mitochondrial neurogastrointestinal encephalomyopathy; Thymidine phosphorylase; TYMP